Multiple-joint neurons in somatosensory cortex of awake monkeys

(1) In the somatosensory cortex of alert monkeys, 55 neurons were found which receive convergent information from two or more adjacent joints. Most of these multiple-joint neurons were excited by postures of the hand, particularly those involved in grasping. (2) Three basic types of joint interactions were observed. The simplest neurons (occlusion neurons) responded to postures of several different joints, but combination of the preferred postures produced no further increase in firing. The more complex cells showed summated responses to combined postures of adjacent joints, or subliminal facilitation between joints. The responses of both summation neurons and subliminal facilitation neurons were graded with joint angle, and there was an optimum or preferred position for both joints which gave the strongest response. (3) Multiple-joint neurons may provide a neuronal substrate for extracting postural information from several different populations of kinesthetic neurons. They therefore act as feature-detecting neurons, abstracting information about specific body postures.