THE INFLUENCE OF THE FOREBRAIN ON AN AUTONOMIC REFLEX

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Abstract
The reflex responses of the nictitating membrane (n.m.) to various intensities and frequencies of stimulation were studied in urethanized eats with the forebrain either intact or sectioned at various levels. The responses of intact animals were found to vary in total extent, in relative proportion of excitatory rebound, and in the duration of after-discharge irrespective of variations in intensity, frequency, or duration of stimulation. These variations were due to sudden and unexplained changes in the "excitability" or activity of the higher "centers" involved in the reflex. Stimulation of the cortex or of the basal ganglia either inhibited or facilitated the reflex responses. Inhibition prevented the effects of excitatory stimulation or its after-discharge only during the period of inhibitory stimulation, i.e., c.i.s. did not cancel c.e.s. permanently. 3 widely separated areas contributed to the excitatory component of the reflex responses of the n.m. These areas were located in the medulla at the region of the pons; at the level of the posterior hypothalamus; and in the cortex (principally that portion lying on both margins and in the depths of the cruciate sulcus). At least 2 areas contributed inhibitory components: the cortical tissue surrounding the presylvian sulcus and extending laterally into the gyrus orbitalis; and an area at the level of the ant. hypothalamus.

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