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. 2013 Oct 9;33(41):16117–16130. doi: 10.1523/JNEUROSCI.5269-12.2013

Figure 5.

Figure 5.

Increasing motivation via expected reward has a differing (push–pull) effect on mean spike rate for target and distractor responses but reduces Fano factor globally. A, Timing (left) and schematic (right) of visually guided saccade task with variable reward. B–E, The PSTHs (B, C) and PSTFs (D, E) show data for large rewards in red and for small rewards in blue. Data in B, D, and F (left column) from target in RF, distractor in surround task condition, and data in C, E, and G from target in surround and distractor in RF task condition. B, C, Population average PSTHs of the spike rate (15 ms non-overlapping bins) show that increasing expected reward increases the mean target-response and decreases the mean distractor response. The left and right graphs in each panel show data aligned to distractor onset and saccade onset, respectively; the left graphs replicate a plot in Falkner et al. (2010) and are reproduced with permission. D, E, Corresponding PSTFs for the Fano factor, however, show a reduction in Fano factor when a larger reward is expected, independent of target location. Gray bar at bottom denotes time window for scatter-plot computation (F, G). PSTFs and PSTHs are as in Figure 1C. F, G, Scatter plot of data from each neuron (calculated as an average of non-overlapping 100 ms windows from 400 ms before to 500 ms after distractor onset, marked in gray in B–E) shows a significant decrease in Fano factor with increased motivation for both conditions (F: p = 0.0008, n = 38; G: p = 0.0030, n = 46; signed-rank test). One point in F (x-axis, 3.10; y-axis, 4.51) and G (x-axis, 4.91; y-axis, 3.36) was omitted from the display for better visibility. Right panels in F and G shows normalized frequency polygons of spike counts for two-example neurons with data from the small (blue) and large (red) reward conditions for each neuron, using the entire analysis window. With larger expected reward, for the neurons in the upper and lower plots, the Fano factor was reduced from 5.29 to 2.37 and 7.12 to 5.41 (target in RF) and from 2.78 to 1.99 and 5.42 to 4.26 (distractor in RF), respectively.