Spatial memory in FEF visual, visuomovement, and movement neurons
Bonnie M. Lawrence & Lawrence H. Snyder
Washington University School of Medicine
St. Louis, MO
Spatial information is temporarily maintained in the frontal eye field (FEF), a cortical area involved in the transformation of sensory signals into saccadic commands. Previous research has implicated FEF visual and visuomovement, but not movement neurons, in spatial memory. We revisited the role of FEF cell types in spatial memory, recording from 87 FEF neurons from two monkeys in a delay saccade paradigm.
Consistent with previous accounts, we found significant delay period activity in the populations of visual and visuomovement neurons (8.6 +/- 3.7 sp/s and 4.3 +/- 1.3 sp/s, respectively; P<.05) but not in the population of movement neurons (0.3 +/- 1.3 sp/s). Surprisingly, when individual neurons were considered, the incidence of significant memory activity in movement neurons (58%) was equal to or greater than that of visual and visuomovement neurons (57% and 32%, respectively).
Typically, memory activity in visual and visuomovement neurons was spatially congruent with visual and movement responses. However, of the movement neurons with significant memory, 40% (6 of 15) were spatially congruent and 60% (9 of 15) were spatially incongruent, with opposite tuning for memory and movement responses. The combined effect of congruent and incongruent responses resulted in the near cancellation of delay period activity across the population of movement neurons.
The encoded information of congruent and incongruent movement neurons was comparable to that of visual and visuomovement neurons. The mean area under an ROC analysis curve was 0.92 for visual neurons, 0.86 for visuomovement neurons, and 0.86 for congruent and 0.81 for incongruent movement neurons.
These results suggest that visual, visuomovement and movement memory neurons contribute roughly equal amounts of spatial information during the delay period. The cancellation of delay period activity in movement neurons may be an important mechanism by which planned saccades are inhibited in FEF.