ELECTROPHYSIOLOGICAL INVESTIGATIONS OF THE SOMATOSENSORY THALAMUS OF THE PIGEON

Somatosensory areas in the thalamus of the pigeon were studied electro physiologically at the single-unit level. Of 459 units, 429 responded to somatosensory stimuli. Of these, 394 units responded specifically t o somatosensory stimuli, whereas 8 responded in addition to visual sti muli and 27 to auditory stimuli also (bimodal neurons). Seven units we re exclusively driven by visual stimuli and 23 units by auditory stimu li. Recording sites included nucleus dorsalis intermedius ventralis an terior (DIVA) and nucleus dorsolateralis posterior (DLP). The number o f bimodal or visual and auditory neurons was much larger in DLP (40%) than in DIVA (7%). This points to a specific somatosensory function of DIVA. There was only a poor somatotopic organization in both nuclei. However, in vertical penetrations, wing representation was usually dor sal to leg representation. Distal parts of the limbs had smaller recep tive fields (RFs) than proximal parts, and the smallest RFs were found on the toes, which seem to be represented in most detail.