Polysensory responses and sensory interaction in pulvinar and related postero-lateral thalamic nuclei in cat

Abstract

Mapping of evoked responses in the pulvinar and adjacent nuclei of the thalamus in the cat under chloralose anesthesia and in the unanesthetized brain (Flaxedil and local anesthesia) was carried out for visual, auditory and somatosensory stimuli. Results have revealed that this region is a polysensory convergence center since all three sense modes produced responses which were widely distributed, although in a regionally differentiated fashion. Visual responses were more prominent in the postero-lateral region than in other regions of the pulvinar or than in other association nuclei. Similarly auditory and somatosensory responses, though overlapping in their spatial distributions, showed a magnitude differential in certain regions, usually those closest to the specific relay nucleus of the particular modality concerned. The nature and distribution of the responses under chloralose and in the absence of general anesthesia (Flaxedil and local anesthesia) were similar but the responses were larger and of longer latency under chloralose. In addition to the mapping of responses a comparison of the latencies was carried out, as well as recovery cycle and intermodality interaction tests. The latency and recovery cycle results tended to confirm the regional differentiation observed in the mapping studies. In the intermodality interaction tests visual stimuli were found to be dominant over auditory and somatosensory stimuli in postero-lateral pulvinar, and auditory stimuli were dominant over somatosensory stimuli. This latter result is discussed in terms of its implications for attentional and discrimination coding of sensory stimuli. Preliminary micro-electrode studies relevant certain temporal correspondences between unit discharges and evoked potentials in the pulvinar, as well as with the secondary or late waves recorded in the visual cortex.