e., looks only backward in time). At each time point, this gave us, across trials, a distribution of firing rates on contralateral trials and a distribution of firing rates on ipsilateral trials. We used ROC analysis to query whether the distributions were significantly different at each time point. By this assay, we found that (113/242) (47%) of cells in the FOF had significantly different contra versus ipsi firing
rates at some point in time during memory trials (overall probability that a cell was labeled as significant by chance p < 0.05; time window examined ran from −1.5 s before to 0.5 s after the Go signal). The temporal dynamics of delay period neurons were quite heterogenous. Different cells had significantly different contra versus ipsi firing rates at different time points during the trial (indicated for each cell in Figure 3 by black horizontal bars). At each time point, we Y-27632 counted
the percentage of neurons, out of the 242 recorded cells, that had significantly different contra versus ipsi firing rates, and plotted this count as a function of time for memory trials and for nonmemory trials (Figure 3C). For memory trials the population first became significantly active at 850 ms before the Go signal (Figure 3C, horizontal orange bar). For nonmemory trials the population became active 120 ms before the Go signal RO4929097 research buy (Figure 3C, horizontal green bar). At the time of the Go signal on memory trials, 28% of cells had firing rates that predicted the choice of the rat. We labeled cells as “contra preferring” if they had higher firing rates on contra trials, and as “ipsi preferring” if they had higher firing rates on ipsi trials. When firing rates were examined across time (from −1.5 s before to 0.5 s after the Go signal), most cells had a label that was consistent across the duration of the trial: 82/89 (92%) of significant delay period neurons were labeled exclusively as either contra-preferring or ipsi-preferring. Seven of the 89 (8%) delay period neurons switched preference at some point during the trial, usually between the MTMR9 delay period and late
in the movement period (data not shown). For our analyses below, we used labels based on the average delay period firing rate. Given the strong difference in contralateral versus ipsilateral impairment during unilateral inactivation (Figure 2), we were surprised to find no significant asymmetry in the number of contra-preferring versus ipsi-preferring delay period neurons: 50/89 cells (56%) fired more on contralateral trials (three examples are shown in Figure 3A), while 39/89 (44%) fired more on ipsilateral trials (three examples in Figure 3B). Although there were more contra preferring cells, the difference in number of contra versus ipsi-preferring cells was not statistically significant (χ2 test on difference, p > 0.2).