The Claustrum, the External Capsule and the Extreme Capsule of Macaca mulatfa' JOSEPH J. BERKE Laboratory of Comparative h'eurology. Depcutment of Am~ton~y, University of Michigan, Ann Arbor, Michiga?z The claustrum is a sheet of gray matter tend beneath the rhinencephalic sulcus situated between the putamen and the (Ariens Kappers, '08; de Vries, 'lo). insular cortex. The external capsule bor- According to Landau ('19) and Faul ders the claustrum medially and separates ('26), the claustrum arises from a ventric- it from the putamen. Interposed between ular matrix, located at the palliostriatal the claustrum and the island is the extreme angle. This gray mass migrates ventro- caps&. Xlost of the interest in the claus- lateralward to lie behind the lower margin trum in past years has centered in onto- of the neocortex and underneath the genetic and phylogenetic studies. No rhineiicephalic cortex. Due to the neuro- biotaxic influence of the ascending fibers agreement has been reached amongst the of the lateral forebrain bundle, the anlage various investigators as to its significance of the claustrum becomes plate-like in and much controversy still exists. configuration. These last authors regarded At present, the knowledge of the fiber the claustrum as independent of both the connections of the claustrum is incom- striatum and the cortex, since their em- plete. The ways in which the basal gan- bryological studies showed no connection glia and the insular cortex are related to of the island with the claustrum during the claustrum and its surrounding cap- ontogenesis. This fact would not favor the sulcs present interesting problems. One theory advocated by Meynert ( 1884), Brod- might speculate that the claustrum serves mann ('09) and Rose ('28) that the as :I relay in the discharge; directly or by claustrum is a derivative of the insula. way of the basal ganglia: from the supple- Moreover, Landau ('23) reported a human mentary motor areas of the cortex to the case in which the insula was absent in tegmc-ntum of the midbrain. the presence of an ipsilaterd claustrum The two capsules that bound the claus- and Dodgson ('55) described a congenitally trum have also not been completely eval- malformed human brain in which the in- uated. There is no consensus regarding sula was present in the absence of the the functional significance or the fiber ipsilateral dorsal claustrum. Furthermore, componeiits of the cxternal and the ex- Macchi ('51) showed that the claustrum treme capsules and the claustrum. is developed before the island becomes differentiated. RET'IETV OF PERTINENT LITERATURE The topographical anatomy of the claus- v-cllious : earlier controversial theories re- arum has been described by Rose ('28). garding the development of the claustrum Klingler ('41), Macchi ('41, '47), and have been reviewed by Ariens Kappers, K511Bn ('51), and was reviewed by Rae I-Iuber, and Crosby ('36). Meynert (1884), ('54a). The claustrum has been divided Brodmann, ('09), Sterzi ('15), and Rose into a compact dorsal part, situated be- ('28) considered the claustrum a deriva- tween the putamen and the insular cortex, tion of the insular cortex. Brodmann ('09) and a ventral portion, which projects for- regarded it as a duplica.tion of the deepest ward into the white matter of the superior layer of this cortex. Ernst de Vries ('10) _-_____ A dissertation submitted in partial fulfillment felt that the claustrum was a part of the of the requirements for the degree of doctor of neopallium, drawn out subcortically to ex- philosophy in the University of Michigan. 297 298 JOSEPH J. BERKE temporal lobe (Macchi, '51; Rae, '54b). the claustrum. Fibers from the insular The ventral claustrum is broken up into cortex enter the extreme capsule and some scattered masses of gray by the fibers of of them continue medially to become inter- the anterior commissure and by the un- mingled with the claustral network (Rae. cinate fasciculus (Papez, '45). Landau '54a) Interconnections between the claus- ('36, '37,'38) described a claustral exten- trum and the insular cortex have been sion beyond the island which he termed described by Berlucchi ('27) and by KatB the claustrum parvum. Kuhlenbeck ('24) ('38) in the cat, by Alettler ('45) ir; the stated that the claustrum was fused with mangabey, and by Rae ('54a) in human the anterior perforated substance. Whit- mateiial. However, simjlar studies 011 the aker ('21) found macroscopic continuity human brain by Cajd ('O2), Piiitus ('32) between the claustrum and the amygdaloid and Itlacchi ('48) failed to reveal these nucleus. However, the claustro-amygdaloid fascicles. connections have been denied by Volsch Destruction of the frontal cortex anterior ('06),Hilpert ('28),and Broclthaus ('38). to the motor area in monkeys produced Nevertheless it is generally considered that degeneration in the claustrum according to portions of the ventral claustrum lie adja- Bianchi ('22) and lesions in areas 9 and cent to the amygdala, the superior tem- 11 of the macaques permitted denionstra- poral gyrus, and the ventral part of the tion of fiber connections to the claustrum, frontal lobe (Rae, '54a). according to Mettler ('35a, '47). Con- A detailed study of the microscopic struc- tinuity between the ventral claustrum and ture of the human claustrum was made by the gyrus olfactorius lateralis was noted Rae ('54a). Other descriptions of the by vcin Economo in 1929. Macchi ('48, microscopic anatomy of this region have '51), Landau ('19), and Rose ('28) de- been reported by Pintus ('30, '31), Brock- scribed connections of the claustrum with haus ('38, '40), and Nacchi ('48). The the olfactory area. These were disputed dorsal and the ventral claustrum are histo- by Spiegel ('19) and by Brockhaus ('42) logically similar. Silver preparations show Berlucchi (cat, '27) and Papez (man, '45) a network of fine and medium-sized fiber dcmonstrated fibers originating from the fascicles extending in various planes, piriforni cortex and passing around the with the bodies of the claustral cells in the frontal surface of the amygdala to reach interstices. The cell bodies are triangular, the claustrum. ovoid, fusiform or pyramidal in shape, with Hiras'twa and coworkers ('38) described the fusiform cells most numerous near the fibers from area 22 of the temporal cortex external and extreme capsules, and the to the claustrum, in support of Volsch's other types distributed at random (Rae, ('10) contention that the claustrum of '54a). The fusiform cells, which are typ- apes had fiber connections with the tem- ically oriented with their greatest diam- poral lobe. Macroscopic continuity bc- eters in the vertical plane, have been stud- tween the ventral claustrum 2nd. the rimy&- ied by several observers (V. Bechterew, daloitl nucleus has been reporrcd (Pilitus. 1899; Spiegel, '19; Kuhlenbeck, '24). The '31; Macchi, '48), although no filler con- large number of this type of cell is re- nections have been found. However. in garded as characteristic of the claustrum. Didelphis, van der Sprenkel ('26) re- In the literature to date, scanty informa- ported fibers in the lateral olfactory nu- tion has accumulated concerning the fiber cleus, which reached the contralnteral ex- connections of the claustrum 2nd much ternal capsule and the claustrum by way controversy still exists concerning those of the anterior commissure. This state- connections which have been reported. An ment W~Ssupported by Fox, McKinley and exchange of fibers between the external Magoun ('44), who stimulated the lateral czpsule and the lateral border of the puta- part of the olfactory bulb in the cat and men has been described by Wilson ('14), recorded positive potentials in the claus- Kodama ('27), Pintus ('32),hlacchi ('48), trum Le Gros Clark and Meyer ('47) re- and Rae ('54a). These fibers are not nu- moved the olfactory bulb but were unable merous in any one field, however, and it is to find degeneration in the claustruin of uncertain whether any of them arise in the rabbit. CLAUSTRUM, EXTERNAL AND EXTREME CAPSULE OF MACAQUE 299 Claustronigral or claustrotegmental con- sule (Dejerine, 1895; E. Smith, '31; Lauer, nections were suggested by the experi- '45). mental lesions of Rosegay ('44) in the cat. The geniculotemporal bundle and the Recruiting waves have been displayed in ventral thalamic radiations contribute the claustrum from stimulation of the fibers to the capsules. Vestibular and ol- centromedian and the interlaminar nuclei factory fibers (Papez, '45) have also been of the dorsal thalamus (Starzl and Ma- described. Temporal projection fibers in goun, '51). the extreme capsule have been noted (Bucy Many theories have been presented re- and Kluver, '55). Fibers from the inferior garding the functions of the claustrum and thalamic peduncle turn into the basal these have been well summarized by Rae claustral complex. Other projection fibers ('54b). Certain observers (Randacio, from the ipsilateral motor cortex (Hira- 1882; Kuhlenbeck, '24; Macchi, '48, '51) sawa and Kariya, '36) are contained within have considered the claustrum as part of the capsules. Whether any of these fibers the olfactory complex. Physiological eri- terminate in the claustrum has not been dence (Fox et al., '44; Rae, '54b; Segundo determined. Fibers of the ansa lenticularis and Machne, '56) suggests that this area is originating in the caudate nucleus have a correlation center for olfacto-visceral- been regarded by Foix and Nicolesco ('25) somatic impulses. Pintus ('32) and Lan- as passing in the external capsule with dau ('36) believed that the claustrum is some termination in the claustrum. related to the production of speech. Ariens Kappers ('08) felt that the claustrum MATERIALS AND METHODS exerts some effect upon motor responses, In this investigation, the experimental a conclusion which has been supported by subjects used were monkeys (Macaca the results of Mettler et al. ('39) and Kaada mulatta). Nine animals, with weights ('51), who found that movements evoked ranging between 2 and 7.2 kilograms, were from cortical excitation were inhibited chosen without preference for sex.