16846 • The Journal of Neuroscience, October 16, 2013 • 33(42):16846–16852 Systems/Circuits Distinct Parietal and Temporal Connectivity Profiles of Ventrolateral Frontal Areas Involved in Language Production Daniel S. Margulies1 and Michael Petrides2 1Max Planck Research Group: Neuroanatomy & Connectivity, Max Planck Institute for Human Cognitive and Brain Sciences, 04103, Leipzig, Germany, and 2Cognitive Neuroscience Unit, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4 Broca’s region, which in the language-dominant hemisphere of the human brain plays a major role in language production, includes two distinct cytoarchitectonic areas: 44 and 45. The unique connectivity patterns of these two areas have not been well established. In a resting-state functional connectivity study, we tested predictions about these areas from invasive tract-tracing studies of the connectivity of their homologs in the macaque monkey. We demonstrated their distinct connectivity profiles as well as their differences from the caudally adjacent ventral parts of the premotor cortex and the primary motor cortical region that represent the orofacial musculature. Area 45 is strongly connected with the superior temporal sulcus and the cortex on the adjacent superior and middle temporal gyri. In the parietal region, area 45 is connected with the angular gyrus, whereas area 44 is connected with the supramarginal gyrus. The primary motor cortical region in the caudal precentral gyrus is not connected with the posterior parietal region, which lies outside the confines of the postcentral gyrus, whereas the ventrorostral premotor cortical area 6VR, in the most anterior part of the precentral gyrus, has strong connections with the rostral supramarginal gyrus. Thus, area 44, which has stronger connections to the posterior supramarginal gyrus, can be distinguished from both the adjacent area 6VR and area 45. These findings provide a major improvement in understanding the connectivity of the areas in the ventrolateral frontal region that are involved in language production. Introduction resonance imaging (MRI), which have also provided evidence for The traditional view has been that Broca’s region, the anterior axonal connections between the inferior parietal and lateral tem- language region of the human brain composed of the distinct poral regions and the ventrolateral frontal region (Catani et al., cytoarchitectonic areas 44 and 45, is primarily connected with the 2005; Croxson et al., 2005; Anwander et al., 2007; Frey et al., 2008; posterior part of the superior temporal gyrus (Geschwind, 1970). Morgan et al., 2009). However, the specific areas of origin of The recent discovery of the cytoarchitectonic homologs of areas axonal connections in the enormous expanse of cortex that are 44 and 45 in the macaque monkey (Petrides and Pandya, 1994, the parietal and temporal lobes and their termination points in 2002; Petrides et al., 2005) made it possible to examine their ventrolateral areas 44 and 45 (Broca’s region), the premotor area precise anatomical connectivity using invasive tract tracers 6VR, and the primary motor area 4 cannot be unambiguously (Petrides and Pandya, 2009). The macaque monkey studies dem- established using diffusion MRI-based approaches (Johansen- onstrated highly distinct connectivity profiles for areas 44 and 45, Berg and Behrens, 2006; Jones, 2008; Roebroeck et al., 2008). as well as the adjacent ventrorostral premotor area 6VR that oc- A resting-state functional connectivity analysis in humans cupies the most anterior part of the precentral gyrus, with the provided preliminary evidence that the connectivity profiles of different areas of the inferior parietal and lateral temporal cortex these different areas of the ventrolateral frontal region are similar (Fig. 1), suggesting that this may also be the case for the human to those established in the macaque monkey (Kelly et al., 2010). brain. However, the distinctions between the connectivity profiles of The relevance of the macaque research has been supported by areas 44 and 45 within the parietal and temporal regions, clearly tractography studies of the human brain with diffusion magnetic established in the monkey, were difficult to discern in that group- level analysis. It is important to note that, although area 44 is located primarily on the pars opercularis and area 45 on the pars Received May 26, 2013; revised July 26, 2013; accepted Aug. 15, 2013. triangularis of the inferior frontal gyrus, the considerable vari- Author contributions: D.S.M. and M.P. designed research; D.S.M. and M.P. performed research; D.S.M. analyzed data; D.S.M. and M.P. wrote the paper. ability in the morphology of these two parts of the inferior frontal We thank Ziad Saad for contributing analytic tools. gyrus across individual brains makes it difficult to establish un- The authors declare no competing financial interests. ambiguously their connectivity at the group level. Correspondence should be addressed to Daniel S. Margulies, Max Planck Research Group: Neuroanatomy & The aim of the present resting-state functional connectivity Connectivity, Max Planck Institute for Human Cognitive and Brain Sciences, 04103, Leipzig, Germany. E-mail: [email protected]. study in the human brain was to increase anatomical precision in DOI:10.1523/JNEUROSCI.2259-13.2013 characterizing the cortical connectivity patterns of these ventro- Copyright © 2013 the authors 0270-6474/13/3316846-07$15.00/0 lateral frontal areas by focusing on surface-based individual-level Margulies and Petrides • Distinct Connectivity of Areas 44 and 45 J. Neurosci., October 16, 2013 • 33(42):16846–16852 • 16847 that may be partly masked by the problems in- a 6DC 4 herent in group-level studies. Only after deter- mining the individual-level networks from each 6DR 6DC 4 PGp (Opt) seed region was a group-level analysis conducted, 8B 9 PGa thus avoiding problems of the results being influ- 4 enced by anatomical variability in the initial seed 9/46d 8Ad PFG 10 46 location. 8Av 9/46v PF Data acquisition. fMRI data were acquired 47/12R 6VC 4 3 1 2 from six healthy, right-handed (as assessed us- 45 6VR 44 ing the Edinburgh Handedness Inventory; 47/12 Oldfield, 1971) adult participants (25.3 Ϯ 3.9 3 years old; three females and three males) who ProM gave informed consent. All protocols were ap- proved by the local ethics board of the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany. Resting- state fMRI data were published previously by Taubert et al. (2011). Four datasets were acquired at 2 week inter- vals on a Siemens Magnetom Tim Trio 3 Tesla PGp(Opt) scanner equipped with a 32-channel head coil. b The resting-state fMRI data were acquired with PGa the following parameters while the participants were asked to fixate on a crosshair and remain PFG still: 400 whole-brain volumes; acquisition ma- trix, 64 ϫ 64; slice thickness, 3 mm (1 mm gap); 9/46v PF voxel dimensions, 3 ϫ 3 ϫ 4 mm; 34 slices; TR, 2300 ms; TE, 30 ms; flip angle, 90°; bandwidth, 4 6VC 3 2 1825 Hz; interleaved ascending slice acquisi- 45 1 6VR tion order. The acquisition time for each 44 resting-state scan was 15.3 min. In addition, four T1-weighted anatomical MPRAGE scans were acquired for each individual at 2 week intervals during the same scanning session with the following parameters: TR, 1300 s; TE, Temporal STS 3.46 ms; flip angle, 10°; FOV, 256 ϫ 240 mm; 176 sagittal slices; voxel size, 1 ϫ 1 ϫ 1.5 mm. Preprocessing. Preprocessing of the func- Figure 1. a, Schematic diagram of the architectonic areas of interest along the ventrolateral frontal and inferior parietal cortex tional data in the volume space was conducted inthemacaquemonkeywithanatomicalconnectionsindicated(b).Notethatadjacentareasarealwaysinterconnected.R,Rostral; using a pipeline (scripts available at https:// VR, ventrorostral; VC, ventrocaudal; DC, dorsocaudal; d, dorsal; v, ventral; a, anterior; p, posterior; STS, superior temporal sulcus; github.com/NeuroanatomyAndConnectivity/ ProM, proisocortical motor area. vlpfc_preprocessing_scripts) including com- mands from AFNI (for Automated Functional analysis. Instead of attempting to establish the boundaries between Neuro-Imaging; afni.nimh.nih.gov), FSL (for FMRIB Software Library; www.fmrib.ox.ac.uk/fsl/), and FreeSurfer (https:// the areas of interest, namely areas 6VR, 44, and 45, and to label all surfer.nmr.mgh.harvard.edu). The pipeline consisted of the following main their voxels, we placed a single seed region in the estimated center of preprocessing steps: (1) dropping of first four volumes (3dcalc); (2) slice- each area, as well as in the primary motor cortical area 4. We used 1 h timing correction for interleaved ascending slice acquisition (3dTshift); (3) of resting-state functional MRI (fMRI) data acquired across four motion correction (3dvolreg); (4) skull stripping (3dAutomask); (5) band- scanning sessions from a small group of individuals (n ϭ 6) to im- pass filtering between 0.01 and 0.1Hz (3dFourier); and (6) linear and qua- prove the anatomical specificity of the individual-level connectivity dratic detrending (3dDetrend). Importantly, to avoid cross-sulcal signal analyses. contamination, functional data were not spatially smoothed in the volumet- ric space. Materials and Methods All four MPRAGE anatomical scans were processed together using the Although the areas investigated here each have characteristic topograph- standard FreeSurfer cortical surface extraction pipeline (recon-all).