Neuronal correlates in posterior parietal lobe of the expectation of events.

During studies of response properties of single units in the posterior parietal cortex of 6 awake monkeys, 168 neurons were encountered (7.1% of examined units) which showed anticipatory types of activity. These neurons were found on either side of the intraparietal sulcus. In area 5, this expectation activity was expressed as a change in discharge rate whenever a specific body part (e.g. hand or shoulder) was approached by the investigator as though contact would be made. Invariably the neurons also responded to cutaneous and/or proprioceptive stimulation of the target body area. In area 7a the same type of response was also found but not always with a corresponding somatosensory receptive field. In addition, many neurons increased discharge rates (or rarely, decreased them) immediately prior to the expected occurrence of a reward, a visual task cue, or on hearing the approaching footsteps of a familiar person. None of these responses were correlated to eye movements, nor could they be attributed to any other body movement.