The functional relationship of monkey infra parietal cortex (IPL) to behavior in the extrapersonal space

Lesions of the posterior parietal system in humans and of the presumably homologous area 7 of the monkey cause impairment in high-order manipulative behavior. A specific "misreaching" observed prompted the outlook of dysfunction constrained to the perceptual, the comand/motor aspects excluded. To clarify the nature of normal functioning in this domain, a study was done by microelectrode recording from area 7 of the monkey of neural firing in relation to hand reaching to targets. The data obtained show that an area 7 neuron fires in relation to simple stimuli, such as a square of white light, and to composite stimuli, such as hand reaching by the monkey or by the trainer in the monkey's extrapersonal space, the response to complex stimuli characteristically multiduty. The firing patterns were presumably relatable to encoding of stimulus components with superposed situation variance. Selectivity of the stimulus was maintained along specific invariance, such as to hand used, to direction of outgoing reaching, to direction from which the rewarding hand of the trainer reached. It is proposed that functional linkage of cognate features, a consequent modular category encoding and "packaging" of information relevant for praxis schema, is thus achieved by area 7 cells specialized for integrating information in the time and space domains visual, tactile, proprioceptive/kinaesthetic, and other for the sake of behavior in extrapersonal space. Generalization without jeopardizing of differentiating is presumably enabled through the multiduty cell entity.