Figure 1. Response time sequences. (A) Response time sequences in simple pro-saccade task following GABAA antagonist (bicuculline) injection. These sequences were taken from 4 consecutive blocks of trials for monkey A. (B) Same convention as A when GABAA agonist was injected in the same site. Note the marked increased scatter of both parameters after bicuculline injection, with interleaved normal and markedly impaired values. Each dot corresponds to a saccade. Empty dots: pre-injection trials. Filled dots: post-injection trials. doi:10.1371/journal.pone.0005208.g001 perturbation was further tested in a third animal with a series of injections in the supplementary eye fields and Pre-SMA (Figure S6). For both SEF and Pre-SMA, the variability in response times did not significantly vary following GABAA agonist or antagonist (p&0.5). Two methods were used to further examine the sequences of collected RTs. First, distinct serial correlations of RTs were calculated for each experimental block of trials (preceding or following the micro-injection of GABAA antagonist, GABAA Frontal Cortex and Variability Figure 2. Comparison of GABAA antagonist (bicuculline) and GABAA agonist (muscimol) injections on response times variability (ms). Note the marked effect of GABAA agonist injections and the effect of GABAA agonist on the variability of simple response times. doi:10.1371/journal.pone.0005208.g002 agonist or saline). The correlations were then averaged across sessions and monkeys. Figure 3 shows the average serial correlations obtained for GABAA antagonist, GABAA agonist and saline injections at lags of up to 15 trials. Across monkeys and injection sites, the serial correlations obtained after GABAA antagonist injections is lower than GABAA agonist injections at lags up to 6 trials (U(15,11) = 336, p = .03 ). These results are consistent with the noticeable noise observed following GABAA antagonist injection as shown in Figure 1. Then, a series of Lomb-Scargle periodograms were calculated for the different subsequences of trials following the injections. The resultant power spectra were averaged across monkeys and sessions. Similar to what has been reported previously in the literature, the power of RTs oscillations following injection of GABAA agonist is centered in the lowest part of frequencies Figure 3. Serial correlations between response times (RTs). Average of correlations for 16 sites of monkeys A and B. The different correlations estimated from sequences preceding (thin line) or following injections (thick line) of GABAA agonist (blue line) and antagonist (orange line) are plotted separately. The correlations between RTs and past RTs are presented at lags up to 15 trials. doi:10.1371/journal.pone.0005208.g003 PLoS ONE | www.plosone.org 2 April 2009 | Volume 4 | Issue 4 | e5208