Figure 2: Persistent activity is a predominant property of V4-projecting FEF neurons.

(a) Response of an example V4-projecting FEF neuron during the spatial WM task in which monkeys made saccades to remembered locations based on a cue at the start of the trial. Neuronal response histogram plots the response of an example FEF neuron on trials when the WM cue appeared in the neuron’s RF (yellow) or outside of it (blue). The FEF neuron exhibited elevated activity during both the visual and the delay (memory) periods of the task on trials when the cue appeared in the RF, but activity dropped to baseline before saccade onset. Shaded area indicates ±1 s.e.; FP, fixation point. (b) The peristimulus time histogram (bottom) shows the average normalized activity of all V4-projecting FEF neurons (red, n=15) versus FEF neurons not projecting to V4 (blue, n=307), for trials when the WM cue appeared in the neuron’s RF. The histograms (top) show distributions of average selectivity of 1,000 15-neuron ensembles, each selected randomly from the 307 non-projecting FEF neurons. Selectivity was quantified as the ROC for WM in the RF versus outside the RF, separately for the visual, delay and saccade periods. Red vertical lines indicate the average selectivity for the 15 V4-projecting neurons; the location of this mean relative to the distribution of non-projecting ensembles indicates the likelihood that the V4-projecting population differs significantly from the general population in selectivity during this period. Red, green and blue bars along the x axis indicate the time window used in analysis for the visual, delay and saccade periods, respectively.