Manipulation reach and visual reach neurons in the inferior parietal lobule of the rhesus monkey.

The characteristics of inferior parietal lobule (IPL) 'reach cell' responses were studied in the fixating monkey in order to obtain a clue to the function of this area in manipulative behavior. Two subclasses of reach neurons, one showing visual receptive field sensitivity, the other lacking such responsiveness are proposed as correlates of two types of reach behavior, one that takes place with, the other without visual guidance, respectively. Neuronal firing increment and/or firing decrement responses, stimulus-bound to reach behavior were obtained from either type of cell. These were presented as equivalent modes of signal encoding, on the basis of the transformability of neuronal firing increment to firing decrement response as a result of preconditioning stimulation of the oral pulvinar nucleus. Many of the responses obtained were bimodal and some were biphasic, i.e. consisting of incremental and decremental firing phases. As each such component was independently modifiable, they were regarded different signal entities. The multicomponental nature of the visual reach neuronal response was manifested when the reaching movement was into the receptive field of the neuron. Responses consisted then of an initial component, presumably visual, prefixed to a response component stimulus-bound to the reach-invoking stimuli. The early component occupied the same position as the visual response of the cell obtained with visual receptive field stimulation alone. Moreover, the early component could be negated by preconditioning stimulation of the LP and/or pulvinar targets, and then the residual response simulated the response of a non-visual reach neuron.(ABSTRACT TRUNCATED AT 250 WORDS)