Neural Activity in Primate Parietal Area 7a Related to Spatial Analysis of Visual Mazes
Cognitive psychological studies of humans and monkeys solving visual mazes have provided evidence that a covert analysis of the maze takes place during periods of eye fixation interspersed between saccades, or when mazes are solved without eye movements. We investigated the neural basis of this process in posterior parietal cortex by recording the activity of single neurons in area 7a during maze solution. Monkeys were required to determine from a single point of fixation whether a critical path through the maze reached an exit or a blind ending. We found that during this process the activity of approximately one in four neurons in area 7a was spatially tuned to maze path direction. We obtained evidence that path tuning did not reflect a covert saccade plan insofar as the majority of neurons active during maze solution were not active on a delayed-saccade control task, and the minority that were active on both tasks did not exhibit congruent spatial tuning in the two conditions. We also obtained evidence that path tuning during maze solution was not due to the locations of visual receptive fields mapped outside the behavioral context of maze solution, in that receptive field centers and preferred path directions were not spatially aligned. Finally, neurons tuned to path direction were not present in area 7a when a naïve animal viewed the same visual maze stimuli but did not solve them. These data support the hypothesis that path tuning in parietal cortex is not due to the lower level visual features of the maze stimulus, but rather is associated with maze solution, and as such, reflects a cognitive process applied to a complex visual stimulus.