Regional distribution of functions in parietal association area 7 of the monkey

Abstract

The functions of cells in different parts of area 7 were studied in 5 hemispheres of three stumptail macaques (Macaca speciosa). Activity of groups of cells was recorded in non-anesthetized animals using course microelectrodes. Functional maps covering the exposed part of area 7 showed that purely visual and oculomotor responses occurred in area 7a (PG) whereas the skin was dominantly represented in area 7b (PF). Vision was also represented in 7b but here together with somatic mechanisms. Oculomotor discharges were concentrated in the medial part of area 7a, whereas motor action of the arm and hand extended across the medial part of area 7. Motor actions of the mouth were represented most laterally. A statistically significant somatotopic arrangement of the body surface was also observed: the face was represented most laterally and the body and legs most medially with large overlapping regions. In the posterior part of 7a a kinesthetic region was found with representation of joints and muscles. The combination of visual and cutaneous activation was common more laterally than the combination of visual and somatomotor activation. Laterally the visual representation ended at the border between area 7 and area 2 of S I at a locus in front of which the S I receptive fields were located inside the mouth. These results indicate that different functions are represented in different degrees in different parts of area 7. Therefore, one important determinant of the results obtained by various research groups is the area of recording within area 7.