Topographical organization of the thalamic afferent connections to the motor cortex in the cat

The location and topography of motor areas in the cat cerebral cortex were studied by electrical stimulation of the cortex in five animals, and by the injection of retrograde tracers into the spinal cord of four animals. Movements evoked by intracortical microstimulation (ICMS) of the anterior, posterior and lateral sigmoid gyri, both banks of the cruciate sulcus and the dorsal bank of the presylvian sulcus were observed in anaesthetized cats. Fluorescent tracers (Fast Blue and/or Diamadino Yellow) were injected into the lateral funiculus in the second cervical segment, into the gray matter of cervical segments C3-T1 and/or into the gray matter of lumbar segments L2-S1. Contraction of the contralateral forelimb, hindlimb or facial muscles was observed following electrical stimulation of several cytoarchitectonic areas: 4 gamma, 4 delta, 6a alpha, 6a gamma, and 3a. These findings suggested representations of contralateral forelimb and hindlimb movements in areas 4 gamma and 4 delta, and of the contralateral forelimb muscles in areas 6a alpha and 6a gamma. Corticospinal neurons were located in all the above cytoarchitectonic areas as well as in areas 3b, 1, 2, 2pri, and 5. Large numbers of neurons were labeled in areas 4 gamma and 4 delta, and moderate labeling was observed in areas 6a gamma and 6a alpha. Corticospinal neurons projecting to cervical and lumbar segments were located in areas 4 gamma and 4 delta, while those projecting only to cervical segments were detected in areas 6a alpha and 6a gamma. Based on these findings it is proposed that within the motor cortex of the cat there are representations of limb movements in several cytoarchitectonic subdivisions. Many of these representations may be candidate secondary motor areas.

mentioning

confidence: 80%

Section: Comparison With Primatesmentioning

confidence: 94%

Identification of motor areas of the cat cerebral cortex based on studies of cortical stimulation and corticospinal connections

Ghosh

1997

“…In the cases reported here, there was slight spread of tracer, if any, into the underlying white matter and along the injection tract. Other studies (e.g., Moran and Reinoso-Suarez, 1988) have attempted to inject area 4␦ through the medial surface, but we did not attempt that approach, because there was greater probability of intraoperative and postoperative bleeding from the sagittal venous sinus. In any case, significant spread of tracer along the injection tract would involve granular areas using either approach.…”

Section: Injection Sites In 4␥ and 4␦mentioning

confidence: 97%

“…Multiple motor areas in the cat cerebral cortex are suggested by cytoarchitectonic, stimulation, and connectional studies (Hassler and MuhsClements, 1964;Schlag and Schlag-Rey, 1970;Adkins et al, 1971;Guitton and Mandl, 1978;Vicario et al, 1983;Yumiya and Ghez, 1984;Moran and Reinoso-Suarez, 1988;Iwata et al, 1990;Martin and Ghez, 1993;Ghosh, 1997a). The study of cytoarchitecture by Hassler and MuhsClements (1964) subdivided area 4 of the cat cortex into areas 4␥, 4␦, 4sfu, and 4fu.…”

mentioning

confidence: 97%

Comparison of the cortical connections of areas 4? and 4? in the cat cerebral cortex

Ghosh

1997

Area 4 of the cat cerebral cortex has been subdivided into several regions based on cytoarchitectonic studies: areas 4 gamma, 4 delta, 4sfu, and 4fu (Hassler and Muhs-Clement [1964] J. Hirnforsch. 6:377-420). In a previous study, we found separate representations of contralateral limb movements in areas 4 gamma and 4 delta (Ghosh [1997] J. Comp. Neurol. 380:191-214). To investigate the relationship between these representations, the ipsilateral cortical connections of area 4 gamma and 4 delta were compared by the use of the retrograde neural tracers. After intracortical microstimulation of area 4, tracer was injected into one or two of the following regions: the forelimb regions of the rostral and caudal subdivisions of areas 4 gamma and 4 delta (r4 gamma, r4 delta, c4 gamma, c4 delta, separated by the cruciate sulcus) and the hindlimb regions of c4 gamma and c4 delta. Retrogradely labeled neural profiles were counted in every fourth section of the coronal series and located in cytoarchitectonic areas of the ipsilateral cortex. We found topographically organized reciprocal connections between areas 4 gamma and 4 delta; these connections were part of a rich network of interconnections between the cytoarchitectonic subdivisions of area 4. The forelimb regions of c4 gamma and c4 delta, of r4 gamma and c4 delta, and of r4 gamma and r4 delta were interconnected. These findings support the location of a secondary motor area in 4 delta. No interconnections between the forelimb regions of r4 gamma and c4 gamma, and of r4 delta and c4 gamma, could be found. Area 6 (particularly area 6a gamma) was found to project strongly to the forelimb regions of r4 gamma and r4 delta and relatively weakly to the forelimb region of c4 delta. Retrogradely labeled neurons were also detected in areas 3a, 3b, 1, 2pri, 5, 7, and insula after tracer injections in area 4.

“…The little attention that the cerebellopulvinar projection has gained so far may be due to problems of nomenclature and/or the fact that this projection is represented poorly in primates (Chan-Palay, 1977;Kalil, 1981;Rouiller et al, 1994). The primate pulvinar, on the other hand, has been shown to be involved in the execution of visually guided limb movements (Acuna et al, 1990;Chalupa, 1991), and its lateral posterior nucleus projects to the precentral motor cortex, as it does in the cat (Goldman-Rakic and Porrino, 1985;Morá n and Reinoso-Suá rez, 1988;Darian-Smith et al, 1990).…”

Section: Lateralis Posterior-pulvinar Complexmentioning

confidence: 95%

Thalamic territories innervated by cerebellar nuclear afferents in the hedgehog tenrec,Echinops telfairi

Künzle

1998

To gain more insight into the evolution and functional significance of cerebrocerebellar circuits, the cerebellothalamic projections were studied with anterograde tracer substances in the Madagascan lesser hedgehog, tenrec. This insectivore shows one of the lowest size indices among mammals for both the cerebellar nuclei and the neocortex. Almost all cerebellodiencephalic target areas found in the tenrec have been described in other mammals. The intensity and extent of particular projections, however, vary considerably in the tenrec compared with the other mammals investigated so far. The most remarkable finding may be the tenrec's cerebellar projection to the nucleus ventralis medialis. This projection is the most prominent cerebellothalamic projection and originates in predominantly the lateral portion of the cerebellar nuclear complex. The projection to the caudolateral portion of the ventralis anterior complex (VAC) is located immediately rostral to the area receiving ascending somatosensory afferents and appears to originate, in particular, from the intermediate cerebellar nuclear complex. Another cerebellothalamic focus of terminations lies in the paralamellar region of the VAC, whereas the proper intralaminar nuclei, at best, receive a sparse cerebellar input. A faint-to-moderate projection, on the other hand, has been traced consistently to the ventral portion of the lateralis posterior-pulvinar complex and the adjacent dorsal geniculate nucleus. In addition, there are prominent cerebellosubthalamic projections to the zona incerta and the ventral geniculate nucleus. The latter projection is confined mainly to the ventralmost subdivision, which has been shown previously to receive ascending somatosensory, but not retinal, afferents. With the exception of the nucleus ventralis medialis, the projections were essentially confined to the contralateral side.