Spontaneous and evoked activity of the caudate neurons to central and peripheral stimuli after brain lesions

The involvement of the cerebral cortex, commissural fibers and thalamus on caudate-caudate relations was studied in locally anesthetized, paralysed and artificially ventilated cats. This type of experimental preparation was necessary since a complete suppression of spontaneous and evoked activity is produced by subanesthetic doses of general anesthesia. Two types of caudate action potentials were encountered on the basis of their waveform characteristics: biphasic and triphasic spikes, the former being the largest population (80%). These waveforms were independent of the microelectrode resistance and the distance to recorded neurons. However, their responses were very similar to both central and peripheral stimuli. Caudate stimulation depressed the spontaneous discharges of the majority of the responsive units recorded within the opposite nucleus, while striatal neurons were activated by stimulation of the contralateral cortex. Decortication, thalamic lesion (motor nuclei and massa intermedia) and section of the corpus callosum decrease the firing rates of caudate neurons with biphasic spikes, while the discharges of the neurons with triphasic action potentials remained unchanged. Bilateral ablation of the cerebral cortex decreased the responsiveness of striatal neurons to contralateral nucleus and sciatic nerve and reduced the number of spontaneously active cells per recording tract. Section of the commissural fibers also depressed the caudate responses to the contralateral nucleus, and to the opposite precruciate cortex, although thalamic lesion did not affect the responsiveness of caudate cells to both central and peripheral stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)