MODIFICATION OF SENSORY MECHANISMS BY SUBCORTICAL STRUCTURES

Abstract

The effects of conditioning stimuli to subcortical structures upon specific sensory potentials evoked at thalamic and cortical levels were studied in cats. In unanesthetized animals the somatic and visual potentials were modified most easily and the effect was most prolonged when conditioning stimuli were applied to the reticular formation of the brainstem. Conditioning stimuli to the non-specific thalamic system, amygdala, putamen, globus pallidus and head of the caudate nucleus were, in this order, decreasingly effective in modifying sensory impulses. Changes in the evoked responses were more marked at cortical levels than at thalamic levels; similar modifications were observed in the primary and secondary cortical sensory areas. High-frequency (250/sec) stimulation of the reticular formation depresses evoked responses for 10-20 sec; the depression of somato-sensory responses is more marked than the depression of visual responses. Low-frequency stimulation (0.5/sec) to the reticular formation augments the amplitude of evoked visual and somatic responses. A "rebound" depression was observed at times. The reciprocal effect of augmentation and depression of afferent responses appears analogous in some respects to the facilitation and inhibition of motor responses by the reticular system.