The reciprocal associative connections between the first and the second somatosensory area (SI and SII) of the macaque monkey were investigated with the horseradish peroxidase (HRP) procedures. The aim was to determine, in both areas, the laminar distribution of the associative projecting neurones. In a first group of animals HRP was injected in area SII and in a second group in area SI. In the first group of animals it was found that the retrogradely-labelled neurones of area SI sending axons to ipsilateral area SII (SI-SII associative neurones) were distributed overwhelmingly in layer III (88.8%), mainly in the upper half of this layer. Few neurones were also present in layer II (6.1%), IV (1.8%) and V-VI (3.3%). In the second group of animals it was found that the retrogradely-labelled neurones of area SII sending axons to ipsilateral area SI (SII-SI associative neurones) were distributed mainly in layer V-VI (52.4%) and III (41.1%), especially in its upper half. Scattered associative neurones were also found in layer II (2.2%) and IV (4.3%). The different laminar origin of SI-SII and SII-SI associative projections might be related to a different functional role of the two projections in the trasmission of neural information between the two somatosensory areas.
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Con il contributo del Ministero per i Beni e le Attività Culturali