Change in Motor Plan, Without a Change in the Spatial Locus of Attention, Modulates Activity in Posterior Parietal Cortex

Lawrence H. Snyder, Aaron P. Batista, Richard A. Andersen
1998 Journal of Neurophysiology  
recorded for off-line analysis. A square array of eight 3.2-cm butsen. Change in motor plan, without a change in the spatial locus tons surrounding a central fixation button, each of which could be of attention, modulates activity in posterior parietal cortex. J. Neulit by a red or green LED, was located 28 cm from the eyes, rophysiol. 79: 2814-2819, 1998. The lateral intraparietal area subtending 30 1 30Њ of visual angle. Extracellular potentials were (LIP) of macaque monkey, and a parietal
more » ... , and a parietal reach region (PRR) recorded using tungsten electrodes inserted through a recording medial and posterior to LIP, code the intention to make visually cylinder centered at 5 mm posterior and 12 mm lateral (Horsleyguided eye and arm movements, respectively. We studied the effect Clarke coordinates). Single cells were isolated while animals perof changing the motor plan, without changing the locus of attention, formed delayed saccades and reaches to one of the eight peripheral on single neurons in these two areas. A central target was fixated red or green LEDs. Data were collected from cells that had excitwhile one or two sequential flashes occurred in the periphery. The atory responses before movement to at least one target. first appeared either within the response field of the neuron being The effect of changes in motor intention was studied in two recorded or else on the opposite side of the fixation point. Animals adult male rhesus monkeys. Trials began with 750 ms of central planned a saccade (red flash) or reach (green flash) to the flash light fixation in an otherwise dark room (Fig. 1) . A peripheral location. In some trials, a second flash 750 ms later could change flash on opposite sides of the fixation point and either inside or the motor plan but never shifted attention: second flashes always outside the receptive field instructed a saccade (red) or a reach occurred at the same location as the preceding first flash. Responses (green). On half of trials, a second flash occurred at the same in LIP were larger when a saccade was instructed (n Å 20 cells), location as the first, either affirming or countermanding the type whereas responses in PRR were larger when a reach was instructed of movement to be made. (Never, during training or data collection, (n Å 17). This motor preference was observed for both first flashes did an animal experience a trial with sequential flashes in 2 differand second flashes. In addition, the response to a second flash ent locations.) Thus the first flash oriented the animal's attention depended on whether it affirmed or countermanded the first flash; in space and instructed the direction and modality of an upcoming second flash responses were diminished only in the former case. movement. The second flash always occurred at an attended loca-Control experiments indicated that this differential effect was not tion and so never shifted attention but sometimes instructed a due to stimulus novelty. These findings support a role for posterior change in movement type. Finally, the fixation light was extinparietal cortex in coding specific motor intention and are consistent guished, signaling the animal to execute the planned movement with a possible role in the nonspatial shifting of motor intention. (see Fig. 1 for timing). The delay periods of single flash trials and double flash trials were 2,500 and 1,600 ms, respectively. Eight to 12 repetitions of each trial type were performed. Trials
doi:10.1152/jn.1998.79.5.2814 pmid:9582248 fatcat:4cegom4h4zc6nkgglsss4ntih4