Environmental memory in the lateral intraparietal area
演題番号 : S1-2-1-2
Michael E. Goldberg:1 Sara C. Steenrod:1
1:Columbia University College of Physicians and Surgeons
The lateral intraparietal area (LIP) maintains a priority map of space in gaze-centered oordinates which can be used by the oculomotor system to choose the goal of saccads and the visual system to determine the locus of attention (Bisley and Goldberg). This map is predominantly determined by vision, but neurons in LIP have been shown also to response to significant auditory stimuli (Linden, Grunwald and Andersen). Once a location has been established as important, for example as the target of a memory-guided delayed saccade, LIP neurons maintain the location of the important spatial object without requiring further visual stimulation (Gnadt and Andersen). Here we show that this memory continues beyond the confines a single trial. We trained monkeys to make a saccade to a given location which did not excite an LIP neuron. On the next block of trials that saccade brought a recently appeared task-irrelevant stimulus into the receptive field of the neuron; not unexpectedly the cell fired around the beginning of the saccade. After a number of such trials we intermixed trials in which the task-irrelevant stimulus appeared, and trials in which it did not. On the trials in which the stimulus did not appear, the cell fired, albeit with a lower intensity and a longer postsaccadic latency. After a block of trials in which the stimulus was never brought into the receptive field by the saccade the response dissipated. This environmental memory response often required 10 trials to dissipate. We suggest that it represents a spatial memory of an environmental event, which lasts across trials. Control experiments show that the memory could be established without ever stimulating the cell's receptive field as long as the stimulus appeared in a consistent spatial location, nor was the activity dependent on association with a given saccade. Thus the parietal cortex has access to a supraretinal representation of space, which is gated by the appropriate saccade.