Cortical and subcortical patterns of response to afferent vagal stimulation

Abstract

Cortical and subcortical patterns of activity were studied upon electrical stimulation of the cut central end of the cervical vagus nerve in acutely prepared adult cats. The effects of different frequencies and voltages of afferent vagal stimulation were studied while the duration of the stimulus pulses was kept constant (0.75 msec). High-frequency (> 70/sec) low voltage (< 3v) stimulation resulted in the induction of cortical EEG synchronization, while all other combinations of frequency and voltage gave rise to cortical activation. Subcortical structures responded in a manner consistent with the cortical observations. The cerebral cortex and thalamic nuclei responded to synchronogenic vagal afferent stimulus parameters only after an initial latent period, while the hippocampus responded immediately. All responses were bilaterally equivalent and could be induced by either vagus nerve. Severance of both sympathetic trunks and vagi and transection of the neuraxis at the spinomedullary junction indicated that the central responses were neurogenic in origin. These and other studies presently in progress offer convincing evidence that the different cortical responses (synchronization or desynchronization) observed by various investigators from stimulation of the central end of the cervical vagus nerve result from the differential stimulation of specific afferent fiber systems within that nerve.