Search

Responses to vestibular stimulation were recorded from the medullary, spinal, or both portions of the accessory nerve of decerebrate cats. The response consisted of a mixture of autonomic and somatic impulses, the latter particularly contributing to the size of the vestibular evoked activity. Dorsal root stimulation or ventroflexion of the neck strongly interfered with the spinal component of the response. The site of this proprioceptive, inhibitory action was mainly at the spinal level and only to a minor extent may have included supraspinal connections, via cerebellum and brainstem, acting upon the vestibular nuclear complex. The medullary or autonomic component of the accessory nerve response to vestibular stimulation was not under this inhibitory control. Thus, the stream of somatic impulses of importance for postural reflexes is constantly controlled and modified along the executive pathways, while autonomic impulses evoked by vestibular stimulation and given rise to the syndrome of motion sickness are not similarly influenced. The accessory nerves contain afferent fibers which cross the midline and make contact with the contralateral accessory nuclear complex but not with other motor cells within the ventral horn.

A surgical technique has been devised which permits complete neural isolation of the cortex of an entire cerebral hemisphere while preserving the blood supply and drainage. The status of the arterial circulation and venous drainage of the isolated hemisphere is evaluated at the termination of each experiment by comparison of the intact and isolated sides following aortic injection of a particulate dye. Such preparations show continuous or semicontinuous electrical activity consisting of high voltage aperiodic 0.5–4 cycle/sec oscillations and a superimposed lower voltage 25–70 cycle/sec rhythm. This activity may be interrupted by brief isoelectric episodes which may occur in all regions of the cortex simultaneously. The fast rhythm is essentially similar to that seen in the intact brain, and appears to constitute an autochthonic activity of the superficial neural feltwork of the cortex sustained in the absence of afferent neural influences. The high voltage aperiodic slow activity appears to be a consequence of the surgical procedure, but is probably related to neural isolation rather than to circulatory or mechanical insult. The isoelectric episodes are directly related to the physiological condition of the isolated hemisphere, and any factor which tends to compromise this state increases their incidence and duration. The isolated hemisphere is totally inactive only in the presence of significant hypoxia or ischemia. In contrast, the surgically isolated thalamus exhibits continuous rhythmic 6–9 cycle/sec activity of sinusoidal waveform. Thus, the aperiodic slow activity of isolated cortex is not a necessary consequence of deafferentation per se but reflects some characteristic peculiar to the cortex, perhaps a dependence of certain elements of its neural population upon subcortical influences for the development of an organized rhythmic behavior.