Background neuronal activity in cat somatosensory cortex before and after VPL damage. Histogram and taxonomic analysis.

Two groups of cats under barbiturate anaesthesia are used to study the effect of electrolytic coagulation in the VPL of the thalamus on the extracellular unit activity in the somatosensory cortex (the focus of maximum activity (FMA) of this part of the nucleus affected by the lesion). In the first group of animals a comparison is made between the unit activity before and immediately after coagulation, while in the second group of animals the activity of the neurones, recorded in FMA of the intact VPL is compared with that of the neurones in the homologous symmetrical point in the hemisphere, ipsilateral to the VPL coagulate 10-14 days before the acute experiment. The activity of 246 neurones is studied. Histogram, statistical and taxonomic analyses are performed. It is found that lesion in VPL modifies to a certain extent the pattern of neuronal discharges, although even after the damage rhythmic groups of action potentials simultaneous with the spindle-like EEG waves are recorded in the primary somatosensory cortex (FMA). Evidently, the relay VPL nucleus is not the only pacemaker of spindle activity in its projection cortical area, which is in contradiction with some views expressed in the literature.