Intracerebellar Nuclei Research Articles

CEREBELLAR ACTION POTENTIALS IN RESPONSE TO STIMULATION OF VARIOUS AFFERENT CONNECTIONS

CEREBELLAR ACTION POTENTIALS IN RESPONSE TO STIMULATION OF VARIOUS AFFERENT CONNECTIONS

Myograms yielded by faradic stimulation of the cerebellar nuclei

The general characteristics of the muscular manifestations, which ensue on faradic stimulation of cerebellar nuclei, were described in a previous paper (28). In the present investigation an analysis of the nuclear responses was affected by recording the changes in tone in individual muscles of the foreand hindlimbs. Prior to our own work faradic stimulation had been applied to the cerebellar nuclei by Horsley and Clarke (17); they did not record the muscular changes graphically, but only observed the movements of the limb; these movements, to judge from their somewhat casual report, resembled those observed by ourselves. The belief that the responses observed by Horsley and Clarke were evoked by actual stimulation of the nuclei was clearly implied in their article; but in a paper by R. H. Clarke (6), published posthumously, the opinion is expressed that the reactions, supposedly of nuclear origin, were of a fallacious character, depending on current diffusion to Deiter's nucleus and various motor centres. Speaking more particulary for our own work we must state positively that our reactions were evoked by stimulation of the intracerebellar nuclei themselves, and were not due in any sense to spread of current beyond the cerebellum. Phenomena caused by spread of current are readily recognisable, and were avoided by using currents of threshold value for the nuclei, the excitability of which was carefully preserved. Our conclusions are thus more nearly in agreement with those of Horsley and Clarke than with those recorded in the posthumous paper of Clarke.

The Rôle of the Cerebellum in the Co-ordination of Animal Movement

THE intracerebellar nuclei, forming, as they do, important stations on the course of the cerebellar reflex arcs, naturally invite inquiry as to the kind of influence they exert on the muscles. Our observations have been made on the cat, decerebrated in deep anaesthesia according to Sherrington's original technique, the plane of transection of the neuraxis passing just in front of the superior colliculus and in front of the infundibulum, thus leaving intact the nucleus ruber. Horizontal slices were then removed from the cerebellum on one or both sides, so as to expose for stimulation the dorsal surfaces of the nuclei. Measures were taken to arrest the bleeding and to maintain the proper temperature. The approximate position of the nucleus in question having been determined by measurements, the section of cerebellum in this neighbourhood was then carefully explored with minimal currents applied by a unipolar electrode. The following is a brief resume of our results obtained by stimulation of the several nuclei.

The influence of the length of the radiating column on the width of spectral lines

Small differently placed, bilateral lesions were made by transdural coagulation of the cerebellar cortex in the crus II of the cerebellum in 18 cats. In 10 cerebellar halves the lesions were confined to the crus II. The present study is based on these and on 5 halves with some concomitant injury to the dorsal paraflocculus. The ensuing course of the degenerating efferent fibres and the distribution of degeneration in the intracerebellar nuclei were studied with the Nauta31 method and mapped, in most cases in sagittally cut, approximately serial, sections. This facilitated comparisons between cases.The crus II projects onto the nucleus lateralis (NL) as well as the nuclei interpositus anterior (NIA) and posterior (NIP; subdivisions according to Flood and Jansen17). One band of degeneration extends from the dorsocaudal part of the NL, medially and slightly ventrally, through the transition region between NL and NIA into the caudal medial part of the latter. Another band extends from lateral to medial in the rostral part of the lateral half of the NIP.Within both projections there is a topical pattern, less marked in the NIP than in the other band: lateral parts of the crus II project more laterally and ventrally than do medial parts (Fig. 8).The findings demonstrate that the corticonuclear projection of crus II is precisely organized, but there is no strict correlation between lateral and medial parts of the crus II and lateral and medial regions of the lateralis-interpositus complex, respectively, as suggested by Jansen and Brodal21, 22. Even lesions situated most laterally in crus II result in degeneration in the NIP. The pattern of longitudinal subdivisions of the cerebellum which can be recognized during cerebellar corticogenesis24, 25 appears to be considerably distorted during later development.Since there appears to be a somatotopical pattern in the crus II20, 35, it is possible to indicate approximately regions ‘representing’ hindlimb, forelimb and face in the lateralis-interpositus complex.