Electrophysiological experiments of microelectrode recording were performed in the thalamus of the cat in order to study the topography and receptive field (RF) organization of neurones in the trunk representation zone of the nucleus ventralis postero-lateralis (VPL). Experiments were carried out in 6 cats anaesthetized with a mixture of $N_{2}O-O_{2}$ (70% vs 30%) and halothane (0.5%). Three cats had been previously submitted to a single injection of horseradish peroxidase in a physiologically defined site of the trunk zone of the first somatosensory area (SI). Neurones responding to stimulation of trunk RFs were located in the dorsal part of VPL intervening between the lateral (VPLl) and medial (VPLm) subnucleus. Cells located laterally in this zone had RFs on the dorsal midline of the body whereas those located medially had RFs on the ventral midline of the body. The RFs of these neurones were bilateral and straddled, often symmetrically, the respective midline. The neurones of the intermediate region of the trunk zone had only contralateral RFs located on the lateral trunk surface. The RFs found in the region of VPL containing cells retrogradely labelled with horseradish peroxidase were similar to those found at the cortical injection site. The results suggest that the bilaterality of the body midline representation in area SI, described in previous experiments, is imposed by the thalamo-cortical input from VPL nucleus.
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Con il contributo del Ministero per i Beni e le Attività Culturali