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THE JOURNAL OF COMPARATIVE NEUROLOGY 495:691–708 (2006)

Ipsilateral Cortical Connections of Dorsal and Ventral Premotor Areas in New World Owl Monkeys

IWONA STEPNIEWSKA,1 TODD M. PREUSS,2,3 AND JON H. KAAS1* 1Department of Psychology, Vanderbilt University, Nashville, Tennessee 37203 2Division of Neuroscience and Center for Behavioral Neuroscience, Emory University, Atlanta, Georgia 30329 3Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, Georgia 30322

ABSTRACT In order to compare connections of premotor cortical areas of New World monkeys with those of Old World macaque monkeys and prosimian galagos, we placed injections of fluo- rescent tracers and wheat germ agglutinin-horseradish peroxidase (WGA-HRP) in dorsal (PMD) and ventral (PMV) premotor areas of owl monkeys. Motor areas and injection sites were defined by patterns of movements electrically evoked from the with microelec- trodes. Labeled neurons and axon terminals were located in sections cut either in the coronal plane or parallel to the surface of flattened cortex, and they related to architectoni- cally and electrophysiologically defined cortical areas. Both the PMV and PMD had connec- tions with the primary (M1), the (SMA), cingulate motor areas, somatosensory areas S2 and PV, and the posterior parietal cortex. Only the PMV had connections with somatosensory areas 3a, 1, 2, PR, and PV. The PMD received inputs from more caudal portions of the cortex of the lateral and more medial portions of the posterior parietal cortex than the PMV. The PMD and PMV were only weakly interconnected. New World owl monkeys, Old World macaque monkeys, and galagos share a number of PMV and PMD connections, suggesting preservation of a common from early primates. Comparisons of PMD and PMV connectivity with the cortex of the and posterior parietal cortex of owl monkeys, galagos, and macaques help identify areas that could be homologous. J. Comp. Neurol. 495:691–708, 2006. © 2006 Wiley-Liss, Inc.

Indexing terms: motor cortex; posterior parietal cortex; motor system; primates; primate evolution

The cortical motor system appears to be exceptionally 1991a–c; Wu et al., 2000; Fang et al., 2006), and humans well developed in primates. In addition to the primary (e.g., Fink et al., 1997; Geyer et al., 2000). Thus, the motor cortex (M1), which is common to all eutherian mam- cortical motor system has a number of matching subdivi- mals (Beck et al., 1996), primates have well-differentiated sions in prosimian (strepsirhine) primates, platyrhine an- dorsal (PMD) and ventral (PMV) premotor areas, a sup- thropoids (New World monkeys), and catarhine anthro- plementary motor area (SMA), a frontal eye field (FEF), and two or more cingulate motor fields (Kaas, 2004a). The organization and connections of these areas have been particularly well studied in macaque monkeys (Godschalk Grant sponsor: National Institutes of Health; Grant number: NS 16446. et al., 1995; Picard and Strick, 1996; Rizzolatti et al., 1998; *Correspondence to: Jon H. Kaas, Department of Psychology, Vanderbilt for review, see Wise et al., 1997; Luppino and Rizzolatti, University, 301 David K Wilson Hall, 111 21st Ave. South, Nashville, TN 2000; Picard and Strick, 2001; Dum and Strick, 2002), but 37203. E-mail: [email protected]. Received 18 July 2005; Revised 11 October 2005; Accepted 10 November there is good evidence for these areas in New World mon- 2005 keys (Stepniewska et al., 1993; Preuss et al., 1996, 1997) DOI 10.1002/cne.20906 and in prosimian galagos (Preuss and Goldman-Rakic, Published online in Wiley InterScience (www.interscience.wiley.com).

© 2006 WILEY-LISS, INC. 692 I. STEPNIEWSKA ET AL.

TABLE 1. The Cases, Areas, and Tracers Injected Case PMD injection PMV injection M1 Plane of Cut Survival (in days)

90-55L Caudal: DY crystal FL: 3%FB (0.25 ␮l) Coronal 4 Face. 2% WGA-HRP (0.03 ␮l) 91-72L Rostral: 10% FR (0.25 ␮l) FL: 2%WGA-HRP (0.05 ␮l) Coronal 5 92-42L Caudal: 10% FR (0.2 ␮l) Flattened 7 92-83L Caudal: DY pellet FL: FR pellet FL: FB pellet Flattened 9 93-4L FL rep.: DY pellet Coronal 6 94-26L Caudal: 10% FR (0.1 ␮l) FL: 2% WGA-HRP (0.03 ␮l) Flattened 7 Rostral: 2% DY (0.2 ␮l) Face: 3% FB 0.15 ␮l

DY,-diamidino yellow; FB, fast blue; FL, forelimb; FR, Fluoro Ruby; WGA-HRP, wheat germ agglutinin.

poids (Old World monkeys, apes, and humans). Such a movement representations of the PMD and in the forelimb distribution indicates that a constellation of motor areas and face representations of the PMV, as determined by emerged early in primate evolution, in the period from 65 microstimulation mapping (Preuss et al., 1996). In two to 85 million years ago (Martin, 2004) and has been re- cases tracers were also placed in the forelimb representa- tained in the major branches. tion of the (M1). Experimental pro- Whereas the connections of motor and premotor areas cedures were approved by the Vanderbilt Animal Care have been extensively studied in macaque monkeys, and and Use Committee and followed the guidelines of the more recently in galagos, much less is known about such National Institutes of Health. connections in New World monkeys. Major connections of Surgical procedures were described in detail by the M1 have been described in owl monkeys (Stepniewska Stepniewska et al. (1993). All procedures were carried out et al., 1993) and Cebus monkeys (Dum and Strick, 2005), under aseptic conditions. Anesthesia was induced with and the connections of the FEF have been reported for intramuscular injections of ketamine hydrochloride (30 squirrel and owl monkeys (Huerta et al., 1987), but the mg/kg) and xylazine (1 mg/kg), and supplemental injec- connections of PMV and PMD are known only for the tions were given as needed to maintain a surgical level of in Cebus monkeys (Dum and Strick, 2005), anesthesia. Bone covering part of the frontal lobe was and only in part from studies of the connections of the M1 removed and the dura reflected to expose the cortex from in owl monkeys (Stepniewska et al., 1993) and the frontal the (CS) to the dimple of the inferior arcu- eye field in owl monkeys and squirrel monkeys (Huerta et ate sulcus (IAS). The cortex was covered with silicone oil al., 1987). In the present study, we directly determined to prevent desiccation and to limit brain pulsation. The the connections of the PMV and PMD of owl monkeys. locations of electrode penetrations and tracer injections Injection sites were defined by intracortical microstimula- were marked on a photograph of the exposed frontal lobe. tion, and motor areas were delineated electrophysiologi- After a short microstimulation session to identify areas for cally and architectonically in the same monkeys (Preuss et placing injections (see below), fluorescent tracers (DY, FB, al., 1996). FR) and WGA-HRP were placed in the forelimb and eye- Our study had two main goals. First, we wanted to movement representations of the PMD and in the forelimb compare the cortical connection patterns in owl monkeys and face representations of the PMV (Table 1). In two with those in galagos and macaques. Similarities across cases, an additional tracer was injected into the M1. Trac- these primates would suggest connectional networks that ers were either injected with 1–2-␮l Hamilton syringes have been retained since early in primate evolution, with a glass micropipette attached to the tip of the syringe whereas differences would suggest specializations within needle (0.03–0.05 ␮l of WGA-HRP and 0.1–0.25 ␮lof the different lines of primate evolution. Second, the con- fluorescent tracers) or deposited in the cortex in the form nections of well-defined cortical areas with cortical regions of a crystal or pellet. that are not well understood can help reveal the organi- Following the injections, the cortex was covered with zation of the latter regions. Although the subdivisions of gelatin film, the skull opening was closed with a dental motor and are now reasonably well char- acrylic cap, and the skin was sutured. After a survival acterized in owl monkeys (Gould et al., 1986; Stepniewska period of 4–9 days to allow tracers to be transported, the et al.,1993; Preuss et al., 1996), the organization of the skull was opened again, and additional locations in the posterior parietal cortex in these and other New World same hemisphere were stimulated with a microelectrode monkeys is not well known. Because the PMD and PMV in order to determine the organization of the motor and have dense interconnections with the posterior parietal premotor cortex more extensively. At the end of the stim- cortex in macaques and galagos, such connections in owl ulation session, electrolytic lesions were placed to mark monkeys would indicate the likely locations of areas in the the M1 and PM boundaries and the borders between dif- posterior parietal cortex that have been defined in other ferent body representations within these two cortical re- primates. gions. Lesions to mark cortical locations were made by passing 10 ␮A of direct current for 10 seconds via the microelectrodes. These lesions and other landmarks sub- MATERIAL AND METHODS sequently allowed the electrophysiological results to be Experiments were performed on six adult owl monkeys related to the architecture. Results of the physiological (Aotus trivirgatus). Fluorescent dyes (diamidino yellow and histological investigations are described elsewhere [DY], fast blue [FB], and Fluoro Ruby [FR]) and wheat (Preuss et al., 1996). At the end of the experiment, each germ agglutinin conjugated to horseradish peroxidase owl monkey was given a lethal dose of barbiturate and (WGA-HRP) were placed in the forelimb and eye- perfused through the heart with buffered physiological PREMOTOR CORTEX CONNECTIONS 693 saline, followed by 2% paraformaldehyde in phosphate flattened cortex, boundaries and labeled neurons were buffer, and then by 2% paraformaldehyde in phosphate superimposed in representative sections, providing a flat- buffer with 10% sucrose. Perfused were removed tened surface view (Stepniewska et al., 2005). from the skull and kept in 30% sucrose overnight. In three Photographs were made by using a 35-mm Olympus cases, the cortex was separated from the brainstem and C-35 camera mounted on the Olympus BH-2 microscope. flattened manually between glass slides. The cortical tis- Negatives were scanned at 300 dots per inch with Polaroid sue was sectioned and processed the next day. Sprint Scan 35 scanner (Polaroid, Cambridge, MA). The Microstimulation of the left precentral cortical region digitized images were adjusted for brightness and con- (premotor and motor cortex) was carried out with low- trast, cropped, and pasted in the frame, where text was impedance (0.5–1 M⍀) tungsten microelectrodes inserted added by using Photoshop 7.0 software. Except for con- perpendicular to the cortical surface to a depth of about trast adjustment and cropping, the images were not al- 1.7–1.8 mm (corresponding to layer 5 and upper layer 6). tered in any way. This depth was optimal for eliciting low-threshold move- ment responses from the frontal cortex (Gould et al., 1986; Stepniewska et al., 1993; Preuss et al., 1996). Stimuli RESULTS consisted of single or multiple trains of cathodal current, The ipsilateral cortical connections of the ventral (PMV) with a pulse duration of 0.2 ms, a pulse frequency of 300 and dorsal (PMD) premotor areas of the cortex were re- Hz, and a train duration of 60 ms delivered by a Grass S88 vealed in adult owl monkeys by placing injections of ana- stimulator. At the start of each experiment, we stimulated tomical tracers in these areas and in the primary motor the M1 region with currents generally no higher than 90 cortex (M1). The locations of these areas and some of the ␮A. Then we explored the cortex anterior to the M1 using fields with connections with the premotor cortex are higher currents, although the large majority of premotor shown in Figure 1. The boundaries of the M1, PMD, PMV, sites were responsive with currents of less than 100 ␮A. and SMA were determined in microelectrode stimulation The type of movements and the current thresholds for experiments and correlated with changes in cortical archi- evoked movements were recorded for each penetration. tecture in the owl monkeys (Stepniewska et al., 1993; We considered the movement threshold to be the lowest Preuss at al., 1996). In brief, the PMD and PMV were current that reliably evoked movements detected by each distinguished from the M1 by generally higher thresholds of two observers. for movements evoked by electrical stimulation of the Injected hemispheres were cut at 40 ␮m either in the cortex and by differences in the somatotopic patterns of coronal plane (three cases) or were flattened and cut par- evoked movements. Stimulation of the PMV elicited fore- allel to the cortical surface (three cases). Series of sections limb and orofacial movements, whereas stimulation of the were processed to reveal WGA-HRP (Gibson et al., 1984) PMD elicited movements of the hindlimb, forelimb upper or were mounted unstained for detection of fluorescence. trunk, neck, face, and eyes. Microstimulation results from For cases cut in the coronal plane, additional series of the present cases are illustrated in Preuss et al. (1996). sections were stained for Nissl substance, cytochrome ox- Architectonically, the presence of a thin internal granular idase (CO; Wong-Riley, 1979), acetylcholinesterase layer (layer 4) distinguished the PMV from the M1, (Geneser-Jensen and Blackstad, 1971), or myelin (Gall- whereas the PMD was distinguished from the M1 by a yas, 1979). Flattened tissue was stained for CO, for my- lack of large pyramidal cells in layer 5. Primary sensory elinated fibers, and, in some cases, for Nissl substance. areas (3b, A1, and V1) and the middle temporal visual The locations of cells labeled with fluorochromes were area (MT) were distinguished by their dense CO and my- charted with a Leitz microscope connected to an X-Y plot- elin staining. Other cortical areas were difficult to identify ter, with 360 nm (for FB and DY) and 530–560 nm (for FR) reliably architectonically, and their locations were based wavelength excitation filters. Sections with WGA-HRP on previously established relationships to well-defined label were studied under darkfield illumination, and the cortical areas. locations of HRP injection sites and resulting label were As each of four of the cases had more than one tracer drawn at the same scale as adjacent sections with the injected, the connections of two or three different injec- fluorescent labeling. Both series of sections were then tions could be directly compared within a case. The results superimposed by using electrolytic lesions, sulci, and indicate that the PMV and PMD have sparse cortical blood vessels identified in the tissue sections as guides for connections with each other and denser connections with alignment. the M1, SMA, adjoining portions of , cin- For each case we prepared a composite drawing showing gulate motor areas, posterior parietal cortex, and somato- the relationship of injection sites and transported label to sensory areas of the lateral sulcus. The PMD was more the electrophysiological and architectonic maps of motor, strongly connected with the posterior parietal cortex, premotor, and somatosensory areas. The architectonic def- whereas the PMV had stronger connections with the so- initions of motor and somatosensory areas followed those matosensory areas of the lateral sulcus. of Stepniewska et al. (1993) and Preuss et al. (1996). For the brains sectioned in the coronal plane, a flat surface Connections of PMV view was constructed by drawing the cortical surface of The connections of the PMV, an area that contains each section as a straight line segment and aligning the mainly forelimb and face representation, were revealed in segments for each section along a perpendicular line rep- four cases with a tracer injection centered in the forelimb resenting the crest of the midsagittal fissure. The labeled representation and in one case with an injection in the neurons of each section were projected tangentially onto face representation. As the forelimb representation in the the appropriate line segment, and the reconstruction was PMV is separated from the forelimb representation of the completed by marking architectonic and physiological M1 by a region of face representation, it was possible to boundaries. For the brains cut parallel to the surface of place injections in the physiologically identified forelimb 694 I. STEPNIEWSKA ET AL.

Fig. 1. Subdivisions of cortex in owl monkeys. The locations and sory area [VS]) are hidden within the lateral sulcus. For convenience, somatotopic organizations of motor areas are based on the micro- we have divided the posterior parietal cortex into rostral (PPr), caudal stimulation and architectonic mapping results (Gould et al., 1986; (PPc), medial (PPm), and lateral (PPl) regions. Some visual areas and Stepniewska et al., 1993; Preuss et al., 1996). They include the pri- the primary auditory area (A1) are marked for reference. Visual areas mary motor cortex (M1), composed of caudal (M1c) and rostral (M1r) include the primary (V1), the second visual area (V2), subdivisions; the supplementary (SMA) and pre-supplementary (pre- the third visual area (V3), the dorsolateral area (DL), the middle SMA) motor areas; the dorsal premotor area (PMD), composed of temporal area (MT), and the inferior temporal cortex (IT). Cortical caudal (PMDc) and rostral (PMDr) subdivisions; the ventral premotor areas are demarcated by black solid lines, and somatotopic represen- area (PMV); the frontal eye field (FEF); and the dorsal oculomotor tations within areas are marked with thin dashed lines. Sulci are area (OMD). The cingulate motor cortex on the medial wall consists of marked with gray solid lines. Additional abbreviations: CaS, calcarine rostral (Cgr) and caudal (Cgc) areas. The motor region is bordered sulcus; CgS, ; CC, CS, central sulcus; rostrally by the prefrontal cortex (PFC) and caudally and laterally by FL, forelimb; HL, hindlimb; IAD, inferior arcuate dimple; LS, lateral the somatosensory cortex, which includes areas 3a, 3b (S1), 1, and 2. sulcus; OF, orofacial; STS, ; U.Axial, upper Other somatosensory areas (the second area [S2]; the parietal ventral axial. Scale bar ϭ 5 mm. area [PV]; the parietal rostral area [PR]; and the ventral somatosen- representation of the PMV without involvement of the M1 port extended slightly into the face cortex of the M1 (see forelimb representation. Results were generally very sim- Fig. 9A of Preuss et al., 1996, for the microstimulation ilar across cases with PMV injections, although there were results from this case). Results from a FR injection in the some minor differences in the locations of labeled neurons. eye-movement portion of the PMD in this case provides a The fluorescent tracers yielded only retrograde labeling of useful comparison. As the brain was cut in the coronal cell bodies, whereas WGA-HRP labeled both cell bodies plane, the distribution of labeled cells from these two and axonal terminals. For ease of comparison, only labeled injections is shown in a reconstructed flattened view of the neurons are illustrated. The cases with WGA-HRP injec- cortex with the lateral sulcus opened and the cortex of the tions did, however, indicate that the connections between medial wall adjoining the dorsal view. Labeled neurons the PMV and other regions of the cortex are reciprocal. were scattered across the forelimb region of the primary The characteristic connection pattern of the PMV can be motor cortex (M1), including both the rostral (M1r) and seen in case 91-72 (Fig. 2). In this owl monkey an injection caudal (M1c) subdivisions of the M1, which are distin- of WGA-HRP was placed in the forelimb representation in guished by differences in architecture, connections, and the PMV. The injection core included most of the forelimb responsiveness to microstimulation (Stepniewska et al. region, whereas the injection fringe of dense local trans- 1993; Preuss et al., 1996). More neurons were labeled in PREMOTOR CORTEX CONNECTIONS 695

Fig. 2. The distribution of labeled neurons shown on the dorsolat- and myelin. The dashed lines indicate estimated borders and the eral and medial cortical surface reconstructed from the series of fundus of the lateral sulcus. Electrolytic lesions used to identify bor- coronal sections of owl monkey 91-72L after injections into the rostral ders between physiological zones are marked with crosses (ϩ). For a PMD (black dots) and forelimb representation in the PMV (gray dots). detailed microstimulation map of this case, see Figure 9A of Preuss et Uptake cores of injections are marked with dark colors, black for PMD al. (1996). The lateral sulcus is opened to reveal buried cortex, which and gray for PMV, and diffusion zones with lighter colors. Solid lines is highlighted with light gray. UA, upper axial. Other conventions and mark architectonic borders determined from sections stained for CO abbreviations are the same as in Figure 1. Scale bar ϭ 2 mm.

the M1r than in the M1c. Other labeled neurons were rostral to that of the forelimb in the SMA (Gould et al., located in the caudal forelimb portion of the PMD and the 1986; Preuss et al., 1996). forelimb portion of the SMA (Fig. 1). The labeled neurons Other labeled cells were in the forelimb portion of the in the SMA from the forelimb injection in the PMV were PMD. The cluster of labeled cells just rostral to the PMV caudal to those from the injection in the face-eye repre- injection largely reflects connections with the prefrontal sentation of the PMD. This difference in the distribution of cortex. Labeled neurons were also present in the cortex of labeled neurons is consistent with the microstimulation the medial wall of the , in the location evidence that the representation of the face and eye is of the pre-SMA cortex (Sakai et al., 2000) and in the 696 I. STEPNIEWSKA ET AL. locations of the caudal and rostral cingulate motor areas S2, and VS regions contained labeled cells, as did the (Cgc and Cgr; Fig. 2). lateral part of the posterior parietal cortex. Other connections of the PMV forelimb cortex were with In owl monkey 94-26L (Fig. 5), two injections were somatosensory areas. The lateral focus of labeled neurons placed in the PMV. The more dorsal injection of HRP in area 3a was in the cortex devoted to the forelimb. A few included the digit and wrist representations of the PMV, labeled cells were in the forelimb portion of area 3b (Jain whereas the more ventral injection of FB included the et al., 1998). A large focus of labeled neurons was located region of the PMV devoted to digit and jaw movements just caudal to area 3b in portions of areas 1 and 2 that (see Fig. 7B of Preuss et al., 1996). The two injections represent the forelimb (Merzenich et al., 1978). More of labeled neurons in overlapping regions of the forelimb the labeled neurons were in area 2 than area 1. Large representations of the M1r and M1c, as well as the orofa- numbers of labeled neurons were distributed in several cial region of the M1. Neurons labeled by the two injec- clusters along the upper bank and insula of the cortex tions formed spatially overlapping populations, but there within the lateral sulcus in a caudorostral sequence, indi- were also regions of little overlap. The more ventral injec- cating connections with the second somatosensory areas tion did not appear to label proportionately more neurons (S2), the parietal ventral area (PV), and the parietal ros- in the face M1 than the more dorsal injection. After both tral area (PR; Krubitzer and Kaas, 1990; Qi et al., 2002; injections in the PMV, neurons were labeled in the PMD, Coq et al., 2004). Labeled neurons in the fundus of the SMA, and several locations in the cingulate motor cortex. lateral sulcus were in the location of the ventral somato- Some neurons were labeled in the cortex ventral and ros- sensory area (VS; Cusick et al., 1985; Coq et al., 2004). The tral to the PMV and in two locations near the rostral pole more rostrally located cells in the insula were in the cortex of the frontal lobe. In the somatosensory cortex, neurons that is considered to be somatosensory (Jones and Burton, were labeled in the forelimb portion of area 3a, a few were 1976), but the identity of this cortex is uncertain. Finally, in forelimb 3b, and others were labeled in forelimb and two clusters of labeled neurons were in the lateral poste- possibly face portions of areas 1 and 2. Other neurons rior parietal cortex on the lip of the lateral sulcus. This were present in the lateral sulcus, including the regions of cortex might correspond to areas 7b and/or AIP, as it is the PR, PV, S2, and VS, and in the lateral posterior roughly in the position of the anterior intraparietal cortex parietal cortex. of macaque monkeys, a region known to project to the In summary, there was some variability in the distribu- PMV (e.g., Luppino et al, 1999). tion of labeled cells produced by the different injections in Very similar results were obtained in case 93-4L with the PMV but many consistent features. Injections of area PMV, which represents mainly forelimb and face move- an injection of DY in the forelimb portion of the PMV (Fig. ments, labeled cells in the forelimb and face representa- 3; see Fig. 4A of Preuss et al., 1996 for an extensive tions of several somatotopically organized areas, including microstimulation map of motor and premotor areas in this the M1, PMD, SMA, and 3a, 3b, 1, and 2. The connections case). Again, labeled neurons were located in the forelimb with the PV, S2, VS, and cingulate motor areas may have portion of the M1, especially the M1r, with a few cells also been somatotopically organized as well, but this is uncer- in the orofacial portion of the M1, possibly due to a slight tain because the borders and locations of body parts in the involvement of the injection core in the orofacial part of representations in these areas were more difficult to esti- the PMV. Other labeled neurons were scattered across the mate. The PMV had major connections with the M1; these forelimb representations of the PMD and SMA. This in- connections were denser with the M1r than with the M1c. jection also labeled neurons in the orbital frontal cortex Connections with the SMA, PMD, and cingulate motor ventral to the PMV. Additional foci of labeled cells were areas were less dense and more variable than those with present in the cingulate motor regions. In the somatosen- the M1. Dense foci of labeled cells were observed in so- sory cortex labeled neurons were present in area 3a and in matosensory areas of the lateral sulcus (the S2, VS, PV, lateral portions of areas 1 and 2 in the lateral sulcus and PR), whereas fewer labeled cells were in anterior where the forelimb and face are represented. No labeled parietal areas 3a, 1, and 2. Few or no labeled neurons were neurons were present in area 3b. Labeled neurons were in area 3b. Finally, the lateral portion of the posterior widely distributed across the cortex of the upper bank of parietal cortex, including the cortex along the upper bank the lateral sulcus in regions that included somatosensory of the lateral sulcus, consistently projected to the PMV. areas PR, PV, S2, and VS, and a few labeled cells were in lateral locations in the posterior parietal cortex, possibly Connections of the PMD corresponding to areas 7b and/or AIP, as noted above. In an earlier study, Preuss et al. (1996) distinguished In owl monkey 92-83L, an injection of FR was placed in rostral and caudal divisions of area PMD, based on differ- a portion of the PMV where shoulder, elbow, and wrist ences in architectonics and responses to microstimulation. movements were evoked (see Fig. 9B of Preuss et al., In particular, limb movements were evoked from the cau- 1996). The surface view of the distribution of labeled neu- dal PMD (PMDc), whereas the rostral PMD (PMDr) was rons was reconstructed from brain sections cut parallel to devoted to face, eyes, and proximal forelimb movements. the surface of manually flattened cortex (Fig. 4). Labeled In the present study, injections were placed in the caudal neurons were scattered across the forelimb and adjoining PMD in three cases and in the rostral PMD in two cases. face representations of the M1, in the SMA forelimb rep- The distribution of labeled neurons was similar after in- resentation, and in the cingulate motor cortex. Other la- jections of the PMDc or PMDr but distinctly different from beled neurons were observed in the cortex lateral and the pattern produced by PMV injections. rostral to the injection site. In the somatosensory cortex, The general pattern of PMDc connections can be seen in the forelimb region of area 3a was densely labeled, as were owl monkey 92-42L (Fig. 6), in which a restricted injection portions of areas 1 and 2 along the lip of the lateral sulcus. of FR was placed in the caudal PMD close to the M1 border A few labeled cells were present in area 3b. The PR, PV, (Fig. 7A). At this location, microstimulation produced fore- PREMOTOR CORTEX CONNECTIONS 697

Fig. 3. The distribution of labeled neurons shown on the dorsolat- cells. For a detailed microstimulation map of this case, see Figure 4A eral and medial cortical surfaces reconstructed from the series of of Preuss et al. (1996). EM, eye movements. Other conventions and coronal sections of monkey 93-4 after an injection into the forelimb abbreviations are the same as in Figures 1 and 2. Scale bar ϭ 2 mm. representation of PMV. In this case, each dot represents about five limb movements (see Fig. 7A of Preuss et al., 1996,). The al., 1986). A rostral focus of labeled cells on the medial injection labeled many neurons in adjoining parts of the wall of the cerebral hemisphere was in the location of the PMD, including regions representing movements of the pre-SMA, whereas a more caudal focus was in the location eyes, nose, vibrissae, and forelimb. Other connections of the caudal cingulate motor area. A small cluster of were with the M1r forelimb (Fig. 7B) and trunk represen- labeled neurons ventral to the cingulate sulcus may reflect tations. Labeled neurons were also observed in the SMA, a cingulate somatosensory area (CSMA), similar to that mostly on the dorsal convexity in a region largely devoted described in prosimian galagos (Wu and Kaas, 2003). The to the forelimb. Only a few labeled neurons were present injection in the PMDc did not label neurons in areas 3a or in the PMV, and these were confined to the dorsal PMV. 3b, and only a few neurons were present in areas 1 and 2. Some labeled neurons were present in the cortex lateral to Most or all of the PR, PV, and S2 were devoid of labeled the PMD in the region of the frontal eye field (Huerta et neurons. Dense clusters of cells were present in the depths 698 I. STEPNIEWSKA ET AL.

Fig. 4. The distribution of labeled neurons shown in the flattened 9B of Preuss et al. (1996). The thick line indicates where the dorsal cortex of monkey 92-83L after injections into the PMD (red) the PMV convexity meets the medial wall. Hatching represents tissue damage. forelimb representation (blue), and the M1 forelimb representation Other conventions and abbreviations are the same as in Figures 1 and (green). For a detailed microstimulation map of this case, see Figure 2. Scale bar ϭ 2 mm.

of the lateral sulcus in the VS and deep S2. A few cells pre-SMA. Labeled neurons in the M1 were confined to were labeled in a portion of the lateral posterior parietal forelimb and hindlimb representations in the M1r. A large cortex that also projects to the PMV. However, most of the cluster of labeled neurons was present in the cingulate label in the posterior parietal cortex was in a dorsomedial motor cortex. Anterior parietal somatosensory areas 3a, sector that extended from the dorsal convexity onto the 3b, and 1–2 contained no labeled cells. Among the somato- adjoining medial wall. sensory areas of the lateral sulcus, areas PR, PV, and most Results from a larger injection of DY in the PMDc can be or all of S2 were unlabeled. However, the cortex in the seen in Figure 4. The injection core filled a portion of the depth and in the lower bank of the lateral fissure con- PMDc where microstimulation evoked shoulder and elbow tained many labeled cells, in a region that includes so- movements (see Fig. 9B of Preuss et al., 1996). Labeled matosensory area VS and multisensory areas caudal to neurons were scattered over much of the PMD, and they the primary (Morel and Kaas, 1992; Kaas extended into the frontal eye field and adjoining cortex and Collins, 2004). Labeled neurons were also located just lateral to the PMD. A few cells were in the dorsalmost more caudally along the fundus and upper bank of the part of the PMV devoted to shoulder and elbow move- lateral sulcus, spreading onto the lateral convexity of the ments. Labeled neurons were in the forelimb region of the posterior parietal cortex. Large foci of labeled neurons SMA, where they overlapped labeled neurons from an were located more dorsally in the lateral portion of the injection in the forelimb PMV, but the labeled neurons posterior parietal cortex. Other clusters of labeled neurons from the PMD injection also extended more rostrally into were in the medial posterior parietal cortex and in the the regions of the face representations of the SMA and below the cingulate sulcus. Finally, some PREMOTOR CORTEX CONNECTIONS 699

Fig. 5. The distribution of labeled cells in the flattened cortex after (case 94-26L). For a detailed microstimulation map of this case, see injections into the caudal (red) and rostral (green) PMD, and a rep- Figure 7B of Preuss et al. (1996). Conventions and abbreviations are resentation of the forelimb (blue) and the face (yellow) in the PMV the same as in Figures 1 and 2. Scale bar ϭ 5 mm.

labeled neurons were observed in the cortex rostral to which probably reflects the spread of injection into the visual area MT, a region that may include visual area M1r (Stepniewska et al. 1993). MST and the multisensory cortex ventral to the MST. In case 94-26L (Fig. 5), two small injections of different Only a few labeled neurons were seen in this region in tracers were placed in the PMD, one just rostral to the other cases with PMDc injections (Figs. 6, 8). M1r, centered in the shoulder representation of the PMDc, A similar pattern of label was obtained in case 90-55 and a second more rostromedially in a region of the PMDr (Fig. 8) with a large injection in the most ventral and representing the upper trunk (Fig. 7B of Preuss et al., caudal portion of the PMD, crossing the border into the 1996). Both injections broadly labeled neurons over the M1r so that the injection site involved the forelimb repre- PMD, with a tendency for the more medial injection to sentations of both areas. This case yielded more labeling of label neurons more medially in the PMD. The more medial areas PMV, 3a, and 1–2 than other PMDc injections, injection, which involved the PMDr, also labeled neurons 700 I. STEPNIEWSKA ET AL.

Fig. 6. The distribution of labeled cells in the flattened cortex after an injection into the caudal PMD in monkey 92-42L. For a detailed microstimulation map of this case, see Figure 7A in Preuss et al. (1996). Conventions and abbreviations are the same as in Figures 1 and 2. Scale bar ϭ 2 mm.

more medially in the M1r, including the trunk and hind- dominated (Fig. 9A of Preuss et al, 1996). Labeled neurons limb representations. Both the PMDc and PMDr injec- were distributed throughout the PMD, extending into the tions labeled the forelimb representation in the M1r. Both adjoining FEF. Other labeled neurons were densely injections also labeled neurons in the SMA, but the rostral packed in the rostral part of the SMA, possibly including injection produced a broader distribution of labeled neu- the supplementary eye field (SEF). The rostral M1 con- rons. There were only a few labeled cells present in the tained a number of labeled neurons, whereas the PMV extreme dorsal part of the PMV. The PMDr injection pro- was unlabeled. A few foci of labeled neurons were found in duced clusters of labeled neurons in the cortex of the the frontal granular cortex rostral to the PMD. Labeled medial wall in the regions of the pre-SMA and the rostral cells were also noted in posterior parietal cortex on the and caudal cingulate motor areas. The PMDc injection lateral convexity and along the medial wall of the hemi- yielded fewer labeled neurons in these regions of the me- sphere, as well as in the caudal part of the lateral sulcus. dial cortex. Additional territories with labeled neurons As for somatosensory areas, no labeled cells were observed included the posterior parietal cortex on the lateral con- in anterior parietal areas or in areas PR, PV, or S2, but a vexity and the cortex deep in the lateral sulcus. No labeled few were present along the upper limiting sulcus of the neurons were present in any of the somatosensory fields of insula in or near area VS. the lateral sulcus or the anterior parietal cortex. In summary, the pattern of labeling after PMD injec- As a final demonstration of PMD connections, a FR tions was distinctly different from that after PMV injec- injection was placed in the PMDr of case 91-72L (Fig.2). tions. PMD injections labeled several different locations in The injection was placed in a portion of the PMDr just the posterior parietal cortex, as well as the SMA and medial to the FEF, where nose and eye movements pre- pre-SMA, cingulate motor areas, and rostral (but not cau- PREMOTOR CORTEX CONNECTIONS 701

Fig. 7. Photomicrographs of an injection site of Fluoro Ruby (FR) beled neurons are apparent in the PMD, and labeled axons are ap- in the dorsal premotor area (PMD) and labeled neurons in the pri- parent between the PMD and M1. B: Some of the labeled neurons in mary motor cortex (M1) of owl monkey 92-42L. The cortex was flat- M1. Only the labeled cell bodies were counted, although labeled axons tened and cut parallel to the surface in this case. A: The FR injection and cell fragments are also apparent. Scale bar ϭ 100 ␮minA;50␮m is to the left of an electrolytic microlesion (L) that was placed at the in B. electrophysiologically defined border of the M1 and PMD. A few la-

dal) M1. Injections that involved the eye-movement rep- DISCUSSION resentation of the PMD labeled the FEF and perhaps also In the present study, we injected tracers in the dorsal the SEF. Labeling of the granular prefrontal cortex was (PMD) and ventral (PMV) premotor areas in owl monkeys sparse and variable. Labeling of the PMV was sparse or after these areas were identified by electrical stimulation absent. using microelectrode mapping procedures. The resulting distributions of labeled neurons in the ipsilateral neocor- Connections of M1 tex were related to these maps and to architectonic defi- The present cases with PMV and PMD injections in- nitions of cortical areas published earlier (Preuss et al., cluded two owl monkeys that also had injections of the M1. 1996). The results indicate that both the PMD and PMV These cases allow a comparison in the same case of M1 have connections with the M1 and other motor areas of the connections with those of the PMV and PMD (see frontal cortex. A major difference in the cortical connec- Stepniewska et al., 1993, for a description of M1 connec- tions of the two areas is that the PMV has many connec- tions in other owl monkeys). In owl monkey 92-83 (Fig. 4), tions with somatosensory areas that are early in the hier- the M1 and PMV injections, centered about 4 mm apart, archy of cortical processing, whereas the PMD has fewer both involved forelimb representations, although some of connections with the somatosensory cortex, and these are the cortex involved in the PMV injection represented face with higher level and possibly multimodal areas (Kaas, movements. The PMV injection labeled neurons in and 2004a,b). around the M1 injection core, and the M1 injection labeled Another difference is that the posterior parietal connec- tions of the PMV are restricted to a lateral territory along neurons around the PMV injection core. In the SMA and the lip of the lateral sulcus, whereas the PMD has connec- in the caudal cingulate motor area, the two injections tions with more dorsal and medial regions of the posterior labeled overlapping populations of neurons. In the so- parietal cortex. In the following sections, we discuss the matosensory cortex of the lateral fissure, the two injec- present results in owl monkeys in relation to previous tions labeled overlapping regions of the PV, S2, VS, and studies on cortical organization and connections in owl lateral 1 and 2. In the lateral part of the posterior parietal monkeys and other primates, and we then consider the cortex, along the dorsal rim of the lateral sulcus, neurons functional implications of the findings. We compare re- projecting to the M1 overlapped populations projecting to sults in New World owl monkeys with those in Old World both the PMV and PMD, even though the population macaque monkeys and prosimian galagos to identify sim- projecting to the PMD was largely caudal to one projecting ilar features that were probably present in the earliest to the PMV. Similar results were obtained in a second primates, as well as differences reflecting the evolutionary case, 90-55, with M1 (see Stepniewska et al., 1993) and specializations of the different primate lineages. Finally, PMD injections. The results indicate that the M1 and we use similarities in patterns of connectivity to suggest PMV share several sources of frontal motor and lateral homologies between the posterior parietal fields of New somatosensory connections, whereas the PMV and PMD World and Old World monkeys. share a small zone of lateral posterior parietal connectiv- ity. Overlapping populations of neurons in the SMA, Cgc, Connections of PMV and PMD with other PV, S2, VS, areas 1 and 2, and lateral posterior parietal areas of frontal cortex cortex projected to the hand representations in the M1 The cortical connections of the PMD and PMV in owl and PMV. monkeys are summarized in Figure 9B. The patterns of 702 I. STEPNIEWSKA ET AL.

Fig. 8. The distribution of labeled cells shown on the dorsolateral and face representations in the M1c. (For the resulting distributions and medial cortical surfaces reconstructed from the series of coronal of labeled neurons, see Fig. 12 of Stepniewska et al., 1993.) For a sections of monkey 90-55L after an injection into the caudal PMD. In detailed microstimulation map of this case, see Figure 11B of Preuss this case, the injection spread somewhat into the rostral M1. Addi- et al. (1996). Conventions and abbreviations are the same as in tional injections, marked with dark gray squares, were in the forelimb Figures 1 and 2. Scale bar ϭ 2 mm.

connections revealed by different injections restricted to a involved another field, such as the M1, but the consisten- single premotor area, either the PMD or PMV, were highly cies in results suggest that in most cases other areas were similar, and Figure 9B reflects this consistency across not significantly involved in the injections, nor did the cases and injections. There were also minor differences in injections involve the white matter. results across injections, which could reflect differences in The results indicate that both the PMD and PMV have the efficiency of the tracers employed and variations in the connections with the primary motor cortex (M1). Injec- location of injections within an area, as well as individual tions of the PMD labeled the M1r predominantly or exclu- differences in the connectivity of owl monkeys. In one or sively, whereas injections of the PMV labeled both the two instances, the uptake zone of an injection might have M1r and M1c, although the M1r appeared to be more PREMOTOR CORTEX CONNECTIONS 703 strongly labeled than the M1c in several cases. The inter- orofacial representations of the M1, which are located connections were largely, but not completely, between ventral to the proximal forelimb representation (Fig. 9A). matching body-part representations. These interconnec- Moreover, as in New World and Old World monkeys, the tions were expected because our previous study of connec- connections of the M1 with the PMD in galagos mainly tions of the M1 in owl monkeys revealed labeled neurons involve the caudal PMD. Thus, there are noteworthy sim- in the PMD and PMV that were somatotopically matched ilarities across major primate taxa in the connections of and more dense after M1r injections, and injections in the the M1 with the PMV and PMD. M1c sometimes failed to label any neurons in the PMD or Owl monkey PMD and PMV are also connected with the PMV (Stepniewska et al., 1993). supplementary motor area (SMA), which occupies the me- Additional physiological and anatomical evidence that dial margin of the cerebral hemisphere just rostral to the distinctions exist between the rostral and caudal M1 has hindlimb representation in the M1 (Preuss et al., 1996). been presented in several previous reports (i.e., Strick and The present results indicate that connections of the PMD Preston, 1982a,b; Geyer et al., 1996; Zilles et al., 1996; and PMV with somatotopically matched portion of the Preuss et al., 1997). The differences in premotor connec- SMA may be even denser than those with the M1. In New tions may partly reflect differences in the somatotopy of World Cebus monkeys, the projections from the PMD and the M1r and M1c, as distal (digit) forelimb movements PMV to the SMA are also dense (Dum and Strick, 2005). tend to have greater representation in the M1c Major connections between the SMA and the premotor (Stepniewska et al., 1993), but differences in somatotopy areas, the PMV and PMD, have also been reported in would not appear to account fully for the greater intercon- macaques (e.g., Kurata, 1991; Johnson and Ferraina, nections of the M1r than the M1c with the premotor cor- 1996) and galagos (Fang et al., 2006). The less dense and tex. Instead, it appears that the M1r is more directly more variable connections of the PMV and PMD with involved in premotor cortical functions than is the M1c, rostral and caudal cingulate motor areas in owl monkeys the effects of the M1c on premotor function being medi- were also found in Cebus monkeys (Dum and Strick, ated through its connections with the M1r, which are 2005), galagos (Fang et al., 2006) and macaques (Matelli extensive in owl monkeys (Stepniewska et al., 1993) and et al., 1986; Kurata, 1991; Luppino et al., 2003). Other other primates (e.g., Gatter and Powell, 1978; Huntley connections of the PMD and PMV in the frontal lobe of owl and Jones, 1991; Fang et al., 2006). monkeys are with adjoining parts of the prefrontal cortex. M1 connections with the PMD and PMV have been However, these connections were relatively sparse, as in widely reported in other primates. In particular, the PMD galagos (Fang et al., 2006). In macaques (Barbas and has been reported in New World Cebus monkeys (Dum Pandya, 1987; Preuss and Goldman-Rakic, 1989; Luppino and Strick, 2005) as having the densest input to the M1 of et al., 1993; Lu et al., 1994) and Cebus monkeys (Dum and all frontal cortical areas, although it is not clear whether Strick, 2005), however, there are dense connections be- these connections were concentrated in the rostral M1, as tween the premotor and prefrontal cortex, especially be- in owl monkeys. These connections involve the digit rep- tween the PMV and the cortex surrounding the principal resentations in these areas of Cebus monkeys, which are sulcus. well developed in highly dextrous, tool-using Cebus mon- The PMD and PMV are interconnected, although these keys (Moura and Lee, 2004) but not in owl monkeys. Thus, connections are weak compared with the connections of some differences in the somatotopic distribution of connec- these areas with the M1. Generally sparse connections tions might be expected. Nevertheless, dense connections between the PMV and PMD have also been reported in of the M1 with the PMD and PMV were demonstrated in macaques (see above) and galagos (Fang et al., 2006). The both species of New World monkeys. paucity of connections between the PMD and PMV sug- In macaque monkeys, the regions of the PMD and PMV gests that they are usually involved in distinct and some- both connect densely with the M1 (e.g., Ku¨ nzle, 1978; what independent functions. To the extent that the PMV Matsumara and Kubota, 1979; Muakkassa and Strick, and the PMD are devoted to different body parts, these 1979; Godschalk et al., 1984; Leichnetz, 1986; Matelli et premotor areas would be expected to have few intercon- al., 1986; Barbas and Pandya, 1987; Ghosh et al., 1987; nections. In contrast to other monkeys studied, Cebus Kurata, 1991; Huntley and Jones, 1991; Tokuno and monkeys have distinct digit representations in both the Tanji, 1993; Ghosh and Gattera, 1995; Johnson and Fer- PMD and PMV, and these digit representations are raina, 1996). Digit and orofacial portions of the M1 con- densely interconnected (Dum and Strick, 2005). This ap- nect with the PMV, whereas the proximal forelimb and parent specialization of Cebus monkeys suggests an en- trunk M1 have more connections with the PMD (Tokuno hanced role for these areas in motor control of digits in et al., 1997). Both the PMD and PMV have been divided Cebus monkeys, known for skillful use of their hands into rostral and caudal subareas in macaque monkeys (Westergaard and Fragaszy, 1987). (Barbas and Pandya, 1987; Matelli et al., 1985, 1998), and Connections of the PMV and PMD with the these subdivisions reportedly differ in M1 connections (Fig. 9C). In macaques, the caudal PMD has stronger M1 somatosensory cortex connections than the rostral PMD (e.g., Barbas and Pan- A major difference between the PMD and PMV in owl dya, 1987). In owl monkeys, there is evidence for rostral monkeys is that the PMV is strongly connected with the (PMDr) and caudal (PMDc) divisions of the PMD (Preuss somotosensory areas of the anterior and lat- et al., 1996). As in macaques, the PMDc of owl monkeys eral sulcus, whereas the PMD is not. PMV injections la- appears to have stronger connections with M1. beled areas 3a, 1, and 2 in the anterior parietal lobe. In Finally, in galagos (Wu et al., 2000; Fang et al., 2006), some cases, a few labeled cells were also present in areas connections of the M1 with the PMD are largely from the 3b and 1. The upper bank of the lateral sulcus, in the proximal forelimb and trunk representations of the M1, regions of somatosensory area S2, the parietal ventral whereas the PMV is connected with the forelimb and area (PV), and parietal rostral area (PR), was densely 704 I. STEPNIEWSKA ET AL.

Figure 9 PREMOTOR CORTEX CONNECTIONS 705 labeled after PMV injections. The cells labeled in the an- (Rizzolatti et al., 1998). The physiological properties of terior parietal somatosensory areas after PMV injections neurons in the PMV have been studied in macaques, and were located in regions consistent with the forelimb and many neurons respond to tactile stimuli (Rizzolatti et al., orofacial representations of these areas and thus appeared 1981; Gentilucci et al., 1988; Fogassi et al., 1996; Graziano to match the injected parts of the representation in the et al., 1997). Whereas deactivation of the PMV with mus- PMV. As areas 3a and 2 receive muscle receptor informa- cimol did not notably impair motor performance with the tion from the ventroposterior superior nucleus of the thal- contralateral hand, it did make monkeys less likely to amus (e.g., Cusick et al., 1985), they would largely relay reach with the contralateral hand or reach into contralat- proprioceptive information to the PMV. Inputs from so- eral visual space (Schieber, 2000). matosensory areas PR, PV, S2, and VS in the lateral In contrast to the PMV, the PMD has few connections sulcus would provide somatosensory information that is with unimodal somatosensory cortex in owl monkeys. relayed from areas 3a, 3b, 1, and 2 to the S2 and PV, and Connections originate in or near the ventral somatosen- then to the PR and VS (Kaas, 2004a, b). sory area (VS), and in the more caudal cortex in the lateral The results of studies with injections of somatosensory sulcus, a region that may include the retroinsular area areas provide further evidence for somatosensory input to and part of area 7b (Robinson and Burton, 1980) and area the PMV. In other New World monkeys, area 3b injections CS of Cusick et al. (1989). Whereas neurons in these labeled few if any neurons in the PMV, whereas injections regions are likely to have somatosensory and possibly involving area 3a or areas 1 and 2 did label neurons in the multisensory functions, they are less directly related to PMV region (Krubitzer and Kaas, 1990; Huffman and somatosensory inputs than neurons in the areas of the Krubitzer, 2001; Coq et al., 2004; Padberg et al., 2005). lateral sulcus projecting to the PMV. In addition, these Likewise, injections in the S2 and PV labeled neurons in somatosensory areas project less strongly to the PMD the PMV (Krubitzer and Kaas, 1990; Qi et al., 2002; see than to the PMV. In galagos, similarly, only a few labeled Disbrow et al., 2003 for macaques). Thus, the PMV re- cells were detected in the cortex of the lateral sulcus or in ceives inputs from an array of somatosensory areas that areas 3a and 1–2 after PMD injections (Fang et al., 2006). represent both cutaneous and proprioceptive receptors Macaques also appear to have few or no connections be- (see Qi et al., 2002 for review). tween areas of the anterior or lateral parietal cortex and Studies based on injections of tracers to the PMV in the PMD. other primates have also revealed connections with so- Connections of the PMV and PMD with the matosensory areas. In galagos, PMV injections labeled neurons in areas 3a, 1, 2, S2, and PV (Fang et al., 2006). posterior parietal cortex However, labeling of the cortex in the lateral sulcus was In owl monkeys, both the PMV and PMD have substan- sparse in these animals. In macaques, injections in the tial connections with the posterior parietal cortex. Com- PMV labeled neurons in the regions of the S2 and other paring the parietal connections of owl monkeys with those somatosensory areas of the upper bank of the lateral sul- of macaque monkeys is not straightforward, however, be- cus (Godschalk et al., 1984; Matelli et al., 1986; Barbas cause owl monkeys lack an , which is and Pandya, 1987; Kurata, 1991) and in area 3a (Kurata, an important landmark in macaques and many other pri- 1991). In a study of premotor cortex connections in New mates. In owl monkeys, the lateral sulcus extends quite World Cebus monkeys (Dum and Strick, 2005), connec- dorsally and may extend into the cortex homologous to the tions with the somatosensory cortex were not examined. convexity of the of macaques, and In summary, the functions of the PMV appear to depend possibly even into the homologues of the intraparietal greatly on somatosensory inputs. These inputs could pro- sulcal cortex. In owl monkeys, injections of the PMV la- vide important proprioceptive and tactile information for beled the cortex along the dorsal rim of the lateral sulcus, the guidance of grasping and manipulation movements of the region of labeling extending from the buried upper the hand, some of the proposed functions of the PMV bank of the sulcus across the rim onto the lateral convex- ity (see especially Figs. 2–4). Injections of area PMD also labeled cells in this region, but much more labeling was observed dorsally and medially on the lateral convexity near the medial margin of the hemisphere and on the Fig. 9. Summary of the ipsilateral cortical connections to dorsal medial wall of the hemisphere at the same rostrocaudal (red) and ventral (blue) premotor areas in owl monkeys (B) in com- level (see especially Fig. 2). parison with such connections in other major branches of primate evolution represented by prosimian galagos (A) and macaque mon- In macaques, area PMV is known to be very strongly keys (C). In the left column premotor areas for each primate are interconnected with the anterior inferior parietal cortex marked on the dorsolateral view of the brain. The PMD is divided into (area 7b), the ventral intraparietal area (VIP), and the rostral (pink) and caudal (red) subdivisions in the owl monkey and the anterior intraparietal area (AIP), whereas area PMD is macaque monkey, and the PMv is divided into rostral (light blue) and connected primarily with area 5 in the superior parietal caudal (dark blue) subdivisions in the macaque monkey. The evolu- lobule and with the cortex of the posterior inferior parietal tionary relationship of the three taxa is indicated by the tree diagram on the upper left. In the right column the patterns of connections are lobule, the caudal cortex of the intraparietal sulcus, and shown in the flattened cortex with opened sulci. Dense connections the medial parietal lobe (Ghosh and Gattera, 1995; John- between areas are marked with thick lines, and sparse connections son et al., 1996; Matelli et al., 1998; Luppino et al., 1999; are marked with thin lines. Macaque intraparietal areas: AIP, ante- Nakamura et al., 2001; Tanne´-Gariepy et al., 2002). The rior intraparietal area; LIP, lateral intraparietal area; MIP, medial more posterior and medial parietal areas of macaques intraparietal area; MDP, medial dorsal parietal area; PIP, posterior have gone by a variety of different names; if the nomen- intraparietal area; PO, parietal occipital area; VIP, ventral intrapa- rietal area. Macaque sulci: IOS, inferior occipital sulcus; LuS, lunate clature of Cavada and Goldman-Rakic (1989) is followed, sulcus; PS, principal sulcus. Other conventions and abbreviations are they would include areas 7a, 7ip, and 7m. On this basis, the same as in Figures 1 and 2. Scale bar ϭ 2mminA,B;5mminC. we suggest that 1) the cortex along the dorsal rim of the 706 I. STEPNIEWSKA ET AL. lateral sulcus in owl monkeys labeled by PMV injections is limb as well as oculomotor movements and is strongly homologous to area 7b and possibly also areas AIP and connected to areas in the dorsomedial posterior parietal VIP of macaques; 2) the cortex on the medial wall labeled cortex. In New World and Old World monkeys, and possi- after PMD injections corresponds to 7m; 3) the cortex on bly in galagos, the PMD can be divided into rostral (PMDr) the dorsal convexity labeled after PMD injections includes and caudal (PMDc) regions, each with a different archi- area 5; and 4) the cortex in the caudal portion of the tecture and distinctive physiological properties and con- lateral sulcus corresponds to areas 7ip and 7a, and possi- nections. The ventral premotor (PMV) area represents bly areas MIP and lateral PO. (See Padberg et al., 2005 for orofacial and forelimb movements, and there is no con- a recent comparison of posterior parietal areas in New and vincing evidence in any of these primates that the PMV Old World monkeys, and Cohen and Anderson, 2002, for a represents hindlimb or lower trunk movements to any recent review of intraparietal areas and their proposed significant extent. The PMV is strongly connected to the functions.) areas in the ventral or lateral posterior parietal cortex. In PMD injections in owl monkeys, especially injections all primates studied except Cebus monkeys, the PMD and that involved the PMDr, labeled an additional region of PMV premotor regions are only weakly interconnected. the cortex deep within the lateral sulcus, at the level of, Thus, there are clear similarities in the organization of the and extending posterior to, presumptive area 7b. In ma- premotor region across primates. caques, it appears that the ventral intraparietal area There are also differences in premotor cortex organiza- (VIP) projects to the caudal PMV (PMVc or F4), whereas tion across primates, and these differences primarily in- the adjoining anterior intraparietal cortex (AIP) projects volve the ventral premotor region. In anthropoid pri- to the rostral PMV (PMVr or F5; Luppino et al., 1999), mates, especially in macaques, the PMV represents although others conclude that the VIP projects to the PMD proximal and distal forelimb movements, and it has dense whereas the projection to the PMV comes from the AIP connections with the somatosensory cortex of the lateral and the cortex medial and lateral to the AIP (Lewis and sulcus (the S2, PV, and PR—all areas with prominent Van Essen, 2000; Tanne´-Gariepy et al., 2002). These dif- cutaneous receptor inputs), whereas galagos PMV repre- ferences in interpretation may reflect difficulties in defin- sents only proximal forelimb movements and the PMV has ing boundaries of areas in the intraparietal cortex. In any few connections with somatosensory areas of the lateral case, it appears that the cortex in the caudal portion of the sulcus. Moreover, the PMV in Old World macaques and in lateral sulcus of owl monkeys may correspond to the VIP, New World Cebus monkeys has strong connections with AIP or both areas of macaques. the prefrontal association cortex in the ventral bank of the In macaques, more caudal parts of the posterior parietal principal sulcus, whereas the PMV in owl monkeys or cortex, which have more direct visual inputs, project more galagos has only a few connections with the dorsolateral densely to the rostral PMD (PMDr), whereas more rostro- prefrontal cortex. On the bases of regional differences in medial parts of the posterior parietal cortex, including the physiological properties, connections, and architecture, MIP (the parietal reach region), project more densely to the PMV has been divided into rostral and caudal subdi- the caudal PMD (PMDc; Johnson et al., 1996; Matelli et visions in macaques, but there is no clear basis for such a al., 1998; Shipp et al., 1998; Battaglia-Mayer et al., 2001; distinction in owl monkeys or galagos. These differences in Marconi et al., 2001; Tanne´-Gariepy et al., 2002). Current organization of the ventral premotor region in galagos, proposals suggest that these posterior parietal regions New World owl monkeys, and macaques suggest that the that project to the PMD are part of a network for reaching PMV region changed in evolution to mediate greater con- to objects of interest under visual guidance (Johnson et al., trol of forelimb movements in reaching, grasping, and 1996; see also Cohen and Andersen, 2002; Tanne´-Gariepy retrieving as these behaviors became more important in et al., 2002 for review). New World monkeys and especially in Old World mon- As in owl monkeys, PMD injections in galagos labeled keys. neurons in more medial and caudal portions of the poste- rior parietal cortex than PMV injections (Fang et al., 2006). Recent microstimulation experiments in the poste- ACKNOWLEDGMENTS rior parietal cortex of galagos indicate that reaching move- The authors thank Judy Ives and Laura Trice for tech- ments are evoked from a region of the cortex caudal and nical assistance. medial to the region where grasping hand-to-mouth move- ments were evoked (Stepniewska et al., 2005). Thus, sep- arate parietofrontal circuits for reaching and grasping LITERATURE CITED probably emerged early in primate evolution and have Barbas H, Pandya DN. 1987. Architecture and frontal cortical connections been maintained in the major branches. of the premotor cortex (area 6) in the rhesus monkey. J Comp Neurol 256:211–228. Similarities and difference in the premotor Battaglia-Mayer A, Ferraina S, Genovesio A, Marconi B, Squatrito S, cortex organization of primates Molinari M, Lacquaniti F, Caminiti R.2001. Eye-hand coordination during reaching. II. 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