Somatosensory areas in the telencephalon of the pigeon. I. Response characteristics.

Two somatosensory regions in the pigeon's telencephalon were investigated electrophysiologically with recordings of field potentials as well as single- and multi-unit responses which were evoked by electrical stimulation of all four extremities or by feather movements produced with airpuffs or by hand. The outline of both areas, was studied in detail with the use of grid-like recordings of single or multi-units. One somatosensory area is located rostrally in the hyperstriatum accessorium (HA), rostral to the visual "Wulst". A caudal area comprises the medial aspects of two different cell layers: the neostriatum intermedium (NI) and adjacent neostriatum caudale (NC) as well as the overlying hyperstriatum ventrale (HV). The two areas differ considerably in their response characteristics. Field potentials of the NI/NC-HV area were more complex than those of the HA area and their shapes and latencies varied mainly in dependence of the recording site (NI, NC, HV). Multi-unit responses showed strong excitation and short latencies in NI/NC and weak excitation and longer latencies in HV. Both responses and latencies were uniform in the HA area and latencies generally longer than in NI/NC but shorter than in HV. The HA area processes somatosensory information more specifically. Its neurons have relatively small receptive fields which seem to be arranged in a somatotopic order in such a way that rostral parts of the body are represented superficially and caudal parts in deeper layers. In contrast, the NI/NC-HV area was found to be largely multimodal, receiving also auditory and visual information. Neurons in this region have large somatic receptive fields, often including one and sometimes even both sides of the body surface. A somatotopic arrangement could not be recognized. The whole body surface was representated in both areas, but there was a dominance of wing and back receptive fields in the NI/NC-HV area and leg and neck receptive fields in the HA area.