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.