Functional subdivisions representing different finger regions in area 3 of the first somatosensory cortex of the conscious monkey

Abstract

The representation of fingers in the first somatosensory cortex was studied in conscious monkeys by recording single neuronal activity, and the following results were obtained: (1) In area 3a, most neurons responded to joint manipulation or other types of deep stimuli. The representation of five fingers was somatotopically arranged. (2) In area 3b, 77.7% and 20.9% of identified neurons responded to cutaneous and deep stimuli respectively. (3) Neurons responding to light mechanical stimuli and with receptive fields on the distal finger segment were found in the most anterior part of area 3b while those responding better to specific mechanical stimuli, such as rubbing, scraping, pinching, tapping, etc. of finger glabrous skin, were found in the more posterior part. The representation of the five fingers was somatotopically arranged. (4) Neurons responding to light or specific mechanical stimulation of the dorsal hairy skin of fingers were found in the posterior part of area 3b. The independent somatotopic representation of four fingers was recognized within this region. (5) Neurons responding to mechanical stimulation of the palmar skin were found in two separate regions, the medial one for the ulnar half and the lateral one for the radial half of the palm. (6) These results indicate that the representation of fingers in areas 3a and 3b of the conscious monkey is divided into multiple somatotopic subdivisions each representing a functional region of the hand and fingers. (7) Neurons with multi-finger receptive fields were occasionally found in area 3b, mostly in layer VI. Some of them had inhibitory receptive fields. Multifinger type receptive fields were more commonly found in area 1.