The interpretation of the degenerative changes in the intralaminar nuclei of the thalamus.

Abstract

Although the intralaminar nuclei of the thalamus are now known to have an organized, extrathalamic projection through the internal capsule (Droogleever Fortuyn, and Stefens, 1951;Nashold, Hanbery, and Olszewski, 1955;Powell and Cowan, 1956), the precise mode of termination of the efferents from these nuclei remains problematical. The experimental evidence bearing upon the projection of these nuclei which is available at present permits of two possible interpretations. Because the cells of these nuclei undergo a certain degree of cellular degeneration as the result of large lesions of the cerebral cortex it has been suggested that the intralaminar nuclei send their axons, or axon collaterals, directly to the cortex. On the other hand, because these nuclei show much more severe degeneration after lesions involving the internal capsule and striatum it seems reasonable to conclude that the striatum is in some way implicated in their projection.As it has become apparent that the experimental evidence upon which both of these views are based is inconclusive, we have carried out a number of different types of experiment in an attempt to distinguish between them. In view of certain technical difficulties, however, and because of problems associated with the interpretation of cellular degeneration in these nuclei, the present experiments, by themselves, have also failed to give an unequivocal answer to this question. However, it is considered worthwhile to place the observations on record as they suggest that the relationship of the intralaminar nuclei to both the cortex and the striatum may be different from that which has previously been considered. MATERLAL AND METHODSThe brains of 39 monkeys (Macaca mulatta) were available for this study. In 26 of these brains lesions had been placed in either the caudate nucleus or in the putamen. Most of these lesions were placed stereotactically, but in a few the lesions in the caudate nucleus were made under direct vision through an incision in the rostral part of the corpus callosum. In three brains stereotactic lesions had been placed in the thalamus for another investigation, and the remaining brains had lesions in various parts of the cerebral cortex. All the animals with striatal lesions and four with cortical ablations were allowed to survive for periods ranging between four and 18 weeks. These brains were fixed either in 70% alcohol and 2% acetic acid or in 10% formolsaline, and a regular one in five or one in 10 series of sections throughout most of thc cerebral hemisphere was mounted and stained with thionine. The remaining animals with cortical lesions survived for between one and two weeks, were perfused with 10% formol-saline, and after a further period of fixation were sectioned on a freezing microtome and stained according to the method of Nauta (1957). RESULTSThe first group of experiments to be described was undertaken in order to determine the severity of the cellular changes in the intralaminar nuclei after large cortical lesions. As we are not so much intereste...

Thalamic Projections to Parietal Cortex

“…Thus, the present observations support conclusions that cells in R do not project extensively to the cerebral cortex [Minderhoud, 1971;Scheibel and Scheibel, 1966]. Cortical projections of cells in CL have also been disputed [Albe-Fessard et al, 1971;Murray, 1966;Powell and Cowan, 1967], While the degenerative changes in CL in the present study are not unequivocal, the present HRP findings and those of others [Jones and Leavitt, 1974] confirm the existence of these projections.…”

Aging, brain damage, and psychomotor slowing.

“…The pallidum receives fibers from the striatum and from the intralaminar nuclei and sends fibers to the midbrain reticular formation, centre median of the thalamus, and to the oral portion of the nucleus ventralis lateralis of the thalamus which in turn has the precentral motor area of the cortex as its main projection center (Jung & Hassler, 1960). Several other studies have confirmed the anatomical interconnection of these structures (Carman, Cowan, Powell, & Webster, 1965;Cowan & Powell, 1966;Mehler, 1966;Murray, 1966;Nauta & Mehler, 1966;Powell & Cowan, 1967;Scheibel & Scheibel, 1967;Webster, 1965). The evidence of these studies demonstrates two strong afferent inputs to the corpus striatum: from the intralaminar nuclei of the thalamus and from most areas of the cerebral cortex.…”

An electron microscopic study of the centre-median and ventrolateral nuclei of the thalamus in the monkey

“…The pattern of these connections suggested that the ventrolateral nucleus should be the principal nucleus with which to compare the centremedian as it also receives fibres from the same two sites in the cerebral hemisphere as well as from the deep nuclei of the cerebellum. In some respects the centre-median nucleus is not a typical representative of the intralam inar group (Powell & Cowan 1967), however, in that it does not show any cellular degeneration after removal of the cortex, it is relatively large in primates whereas the intralam inar nuclei as a group are relatively smaller and it is the only element of the group which receives a fibre pathway from the globus pallidus. The morphology and synaptic organization of the two nuclei have been studied in normal brains and the mode of termination of the afferent fibres from the motor cortex, globus pallidus and cerebellum de termined in experimental material after selective damage of these pathways.…”