Behavioral Decision and Unit Divergence Times

<div><p>(A) This figure shows the <i>p</i>-value of the difference between the lick responses in rewarded and unrewarded trials calculated for each block for the data shown in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0060258#pbio-0060258-g005" target="_blank">Figure 5</a>A using a rank sum test at each 0.15-s bin through the trial. As shown in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0060258#pbio-0060258-g005" target="_blank">Figure 5</a>A each bin is allocated a value of 1 if the mouse licked at least once or a value of zero if the mouse did not lick. The rank sum test is performed on all zeros and ones in each bin within each block. The vertical red lines indicate when the <i>p</i>-value drops below 0.05. The horizontal red lines indicate the 0.05 level. The blocks are shown from top (first block) to bottom (last block).</p> <p>(B) Percent cumulative probability plot summarizing the decision times for the 19 go–no-go experiments where at least one unit diverged when the response to the reinforced and unreinforced odors were compared (the experiments contributing to the green wedge in the pie charts in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0060258#pbio-0060258-g004" target="_blank">Figure 4</a>B). The decision time becomes smaller as the animal progresses through the session as evidenced by a shift of the median decision time from 2.5 s for the first block, to 1.0 s for the best block, and 0.95 s for the last block. It is important to state that as explained in the Materials and Methods the actual time of arrival of the odor is delayed ∼300 ms, and therefore what is important in this experiment is not the absolute value of the decision times but rather the relative values.</p> <p>(C) Plot of the <i>p</i>-value of the difference between firing rates between odor A trials and odor AB trials compared at different times throughout the trial for the unit shown in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0060258#pbio-0060258-g003" target="_blank">Figure 3</a>A. <i>p</i>-Values were calculated by using a rank sum test applied to the firing rate calculated in each block in each 0.15-s bin. The horizontal red line is drawn at a <i>p</i>-value of 0.05. The vertical blue lines indicate the time at which the difference in firing rate between odor A and AB dropped below 0.05 for two or more consecutive points. Because of multiple comparisons, the <i>p</i>-value falls below 0.05 occasionally for a single point as seen by the few single data points that fall below the red line in the period before odor responses (−2 to 0 s). We found that two adjacent data points fall below 0.05 only rarely in this prestimulus period (4% of the time) allowing us to use the criterion of two adjacent points below 0.05 as the time when the two rates differ. The vertical red lines are taken form (B) and allow for a comparison of timing between divergent lick behavior and divergent MC firing.</p> <p>(D) Distribution of the difference between unit divergence times and their corresponding behavioral decision times during the best block. The majority of unit divergence occurs after the animal has begun divergent licking behavior (positive values). Only 20% of the units diverge in their firing rate responses to the rewarded and unrewarded odor prior to behavioral divergence of licking.</p>