Ipsilateral Inhibition Research Articles

Binaural interaction in the cat superior olive S segment.

With the exception of low‐frequency characteristic frequency (CF) units, the ipsilaterally evoked discharge of the majority of S‐segment cells can be inhibited with simultaneous stimulation of the contralateral ear. The contralateral inhibitory CF is usually identical to the ipsilateral excitatory CF. The width of the contralateral inhibitory tuning curve is similar to the width of the ipsilateral excitatory tuning curve. Partial inhibition of the ipsilaterally evoked discharge increases the interspike intervals and increases the variability of the discharge. Inhibition, like excitation, is tonically acting. The contralateral inhibitory input with equally intense tones (measured in terms of decibels above threshold) is either about as effective as the excitatory input or less effective, rarely more effective. The primary factor determining the spike output from S‐segment cells is not the absolute intensity level of the stimulus but rather the relative intensity difference of the stimulus at the two ears. [Work supported in part by National Institutes of Health, U. S. Department of Health, Education, and Welfare.]

Responses of the oculomotor units to deep cerebellar stimulation

The influence of electrical stimulations of deep cerebellar formations (nuclei and adjacent white substance) on the unitary discharge of the oculomotor nuclei was investigated in curarized guinea pigs. Different patterns of activation as well as of inhibition of the oculomotor unitary discharge were observed. All the oculomotor units underwent modification following stimulation of the cerebellar nuclei. The most outstanding effects followed stimulation of the dentate nuclei, which usually induced contralateral activation and ipsilateral inhibition of the oculomotor units. Fastigial and interpositus nuclei stimulations provoked facilitation of the oculomotor units regardless of the stimulated site. Stimulation of the white substance surrounding the cerebellar nuclei and of deep cerebellar lamellae was effective only in 71.7% and in 86.6% of cases respectively, although no clear-cut rule could be found for these variations. All the recorded oculomotor units were strikingly modified also by labyrinthine stimulation. Thus a convergence of labyrinthine and cerebellar nuclei impulses on the oculomotor units was shown. In another group of experiments, evoked potentials were recorded from the oculomotor nuclei following single shock stimulation of the cerebellar nuclei. The shortest latencies of the responses were observed after stimulation of the contralateral dentate or interpositus nuclei. On the basis of the latencies of such responses, a direct asynaptic pathway connecting the dentate and interpositus nuclei with the oculomotor nuclei is postulated.

Single unit analysis of cat superior olive S segment with tonal stimuli.

Single unit analysis of cat superior olive S segment with tonal stimuli.

Observations on electrical stimulation of the cerebellar cortex

In recent years Miller (8) and fulton (6) among other authors have produced valuable reviews of the question of cerebellar function. Of primary importance in investigating cerebellar activity by stimulation of its cortex is the fundamental observation of Sherrington (12) that faradisation of the rostral surface produces ipsilateral inhibition of inhibition of decerebrate rigidity. Latterly this observation has been confirmed and amplified by Bremer (1) and by Miller and Banting (7) among others. Electrical stimulation of the anterior lobe inhibits posture in ipsilateral antigravity muscles augments lobe produces spasticity of antigravity muscles on one or both sides. In the pigeon, Which lacks a pyramidal tract, Bremer and Ley (2) Have obtained similar results by excision of, or by stimulation of, the cerebellar cortes. Pollock and Davis (10) have produced similar results in cats by rendering anæmic the anterior part of the cerebellum at the same time as the precollicular neuraxis. Rademaker's animals, from which the entire cerebellum had been ablated, were observed for many months(11) and throughout that time hypertonicity of antigravity muscles was a prominent feature of their symptoms. More recently, Miller and Laughton (9) have described the result of stimulating, not the cerebellar cortex, but the nuclei themselves, which were exposed by ablation of overlying nerve tissue. We proposed therefore to extend these observations by use of a dead-beat recording mechanism, namely, the Sherrington myograph.

Nervous rhythm arising from rivalry of antagonistic reflexes: Reflex stepping as outcome of double reciprocal innervation

The observations with which the present communication deals were met with in experiments continuing those on reciprocal innervation of symmetrical muscles. In my previous paper on that subject it had been reported that in regard to symmetrical extensors of the knee the ratio borne by intensity of the ipsilateral inhibition to the contralateral excitation is such that with equal stimuli to right and left symmetrical afferent nerves there is inhibitory suppression of contraction in both the muscles. In other words, under double reciprocal innervation the ipsilateral inhibition by each nerve completely overcomes the contralateral excitation of the other. It was shown that this mutual suppression holds over a wide range of the scale of intensities of stimulation. It was also shown that with quite weak stimuli a simultaneous stimulation of both nerves, stimuli being equal in intensity, often results in concurrent contraction of both muscles. Indeed, with quite weak stimuli, the effect of stimulation of each afferent nerve by itself is, in the decerebrate preparation, usually contraction of the ipsilateral as well as of the contralateral muscle. This being so, it is evident that at some point in the scale of intensities of stimulation there should be a place below which contralateral excitation is stronger than ipsilateral inhibition, whereas above it ipsilateral inhibition is stronger than contralateral excitation.