In six Java monkeys (Macacus Irus) experiments of neuronal labelling by retrograde transport of horseradish peroxidase (HRP) were performed in order to study the callosal connections of the hand sensory projection field of the second somatosensory area (SII) in the parietal operculum. Under ketamine anaesthesia, 3 monkeys received a single HRP injection ($0.5 \mu l$) and the other 3 monkeys multiple injections ($5-8; 0.5 \mu l$ each) within the deep cortex forming the upper bank of the Sylvian Sulcus. In the first group of 3 animals, the site of enzyme delivery was selected by recording preliminarily with tungsten microelectrodes neuronal responses to somatic sensory stimulation of the hand. Following a single HRP injection in the parietal operculum, HRP retrogradely-labelled cells were found in the first somatosensory area (SI) of the ipsilateral hemisphere (associative cells) and in the thalamic nuclei ventralis postero-inferior and pulvinar oralis. In the contralateral hemisphere, labelled cells (callosal cells) were found mainly in area SII, clustered in a region homotopic to the injected cortex, and a few also in area SI. Following multiple HRP injections which involved large regions of the parietal operculum, labelled cells were found in the ipsilateral area SI and in the following thalamic nuclei: ventralis postero-inferior, pulvinar oralis and medialis, posterior complex, ventralis postero-medialis, and ventral part of ventralis postero-lateralls. In the contralateral hemisphere, numerous callosal neurones were present in several areas of the parietal operculum (areas 3-1-2, SII, 7b and retroinsular) and few also in area SI. Callosal cells of area SII were located in cortical regions corresponding topographically to the hand representation zone.
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Con il contributo del Ministero per i Beni e le Attività Culturali