Processing of tactile and kinesthetic signals from bilateral sides of the body in the postcentral gyrus of awake monkeys.

Earlier studies pointed out that in the primary somatosensory cortex (SI) the receptive fields (RF) of bilateral neurons were related exclusively to the body midline. We recently found a substantial number of neurons with bilateral RFs on hand digits, shoulders/arms or legs/feet in the caudalmost part (areas 2 and 5) of the postcentral gyrus in awake macaque monkeys. The RFs of these neurons were generally of the most complex types found in this region of the cortex, and thus they were considered to be at the highest level along the hierarchical chain of information processing. We conclude that there are two types of bilateral RFs in the postcentral gyrus, one representing the midline structures such as the intraoral cavity, chin or trunk and the other related to limb structures such as fingers, hands, arms, shoulders, legs and girdles. Functional significance of the bilateral activity could be understood in behavioral context as it is seen more extensively in the body parts where bilateral coordination is essential.