Intracellular responses in the centrum medianum-parafascicular complex of the cat following medial and lateral caudate, substantia nigra and peripheral stimulation.

Caudate, nigral and somatosensory stimulation generates brief EPSPs followed by prolonged IPSPs in thalamic neurons of the centromedian-parafascicular complex. A 300 msec long hyperpolarization and inhibition of neuronal excitability represents the predominant effect by virtue of its duration, intensity and constancy. The brief excitatory response which precedes the inhibition is more variable, depending largely upon the site of basal ganglia stimulation. EPSPs tend to remain subthreshold for lateral caudate stimulation whereas medial caudate, medial nigral and somatosensory stimulation usually generates an action potential prior to the inhibitory phase. Double shock stimulation of basal ganglia and limbs at variable intervals demonstrates the predominance of powerful inhibitory interactions between striatonigral and sensory inputs. The existence of these interactions indicates the importance of temporal factors in determining the momentary response of medial thalamic neurons.