surgery. Antibiotics and analgesic were given during the 10 following days. Behavioural tasks Monkeys were trained to look at a central green fixation stimulus for 700–1,200 msec. After a 200 ms blank period (gap), a 2 deg62 deg green target appeared 16 degrees from the fixation target at one of six possible radial locations (0u, 45u, 135u, 180u, 225u, or 315u), during 1,000 ms. After the saccade, the monkey received a reward if the saccade fell within a 5u65u window centered on the target. Failure to enter a 3u63u window around the fixation stimulus or to trigger a saccade within 2000 ms after target onset cancelled the trial. Each task consisted in blocks of 24 trials each in which each radial location was presented semi- randomly. Eye movements were recorded with the search coil technique, as described previously [10]. Localization of the principal sulcus The Figure S1 shows the injected sites. The PS was localized by electrophysiological recordings performed with tungsten microelectrodes (FHC, 8–9 MV at 1 kHz). Electrical stimula- tion (80 ms of biphasic pulses at 350 Hz, current up to 150 mA) was used to delineate the frontal eye field and confirmed that no saccade could be elicited from the posterior sites of this area. Localization of SEF and pre-SMA. In a third control case, injections were made in the SEF and in the pre-SMA. The SEF and pre-SMA were classically localized by electrophysiological recordings performed with tungsten microelectrodes (FHC, 8– 9 MV measured at 1 kHz). Electrical stimulation (80 ms of biphasic pulses at 350 Hz, current up to 150 mA) was used to delineate SEF and confirmed by elicitation of saccade with current as low as 50 mA. The pre-SMA was delineated centro-caudal from the posterior sites of SEF area and rostral to the orofacial region of the SMA. Micro-injection procedure Bicuculline, a GABAA antagonist, or muscimol (Sigma), a GABAA agonist, were injected through a 30-gauge stainless steel cannula lowered into the brain with a transdural guide tube. Once the tip of the cannula was at the desired level, 2.5 ml of bicuculline (5 mg/ml) or 4 ml of muscimol (5 mg/ml) were injected with a 10 ml Hamilton syringe during 16 minutes. In monkey A, 10 sites were injected with bicuculline, four of them being injected with muscimol. In monkey B, bicuculline was injected at 6 sites, all these sites being also injected with muscimol. Data analysis Saccades were identified offline and controlled visually. In each experiment, we analyzed primary saccade latency, gain and direction. Saccade gain was defined as the ratio of primary saccade amplitude and target eccentricity. Saccade direction was determined in degrees (positive values: from 0u to 180u counterclockwise, negative values: from 0u to 180u clockwise). For each saccade, we determined its directional accuracy by calculating a directional error in degrees. Thus, a +5u directional error corresponds to a saccade with a slightly counterclockwise deviated direction. The directional error was obtained by subtracting saccade direction from target direction, i.e. the ideal vector that would have been required to acquire the target. Frontal Cortex and Variability Statistical analyses Differences between groups were assessed using the rank sum test, also referred as Mann-Whitney test (Matlab2008b, Math- works). This test was used so that the normality of the populations was not assumed. Level of significance was set to p = 0.05. Correlations were calculated using Spearman rank order test. Supporting Information Text S1 Found at: doi:10.1371/journal.pone.0005208.s001 (0.02 DOC) MB Figure S1 Injection sites. (A) Injection sites in the region of dlPFC for monkey A. Orange dots represent sites at which GABAA antagonist (bicuculline) was injected. Blue circled dot represent sites at which GABAA agonist (muscimol) was injected. PS: principal sulcus. AS: arcuate sulcus. (B) Same conventions for monkey B. Found at: doi:10.1371/journal.pone.0005208.s002 (0.65 MB DOC) Figure S2 Variability of response time. (A) Variability of response times as function of experimental session types for monkey A When the eye movement is produced ipsilaterally (full line box) or contralaterally (dotted line box) to the injection site. Blue circled dots represent sites at which both bicuculline and muscimol were injected. (B) Same conventions for monkey B. Found at: doi:10.1371/journal.pone.0005208.s003 (0.37 MB DOC) Figure S3 Variability of saccade amplitude gain as function of experimental and control sessions types. Grey background areas correspond to pre-injection sessions; white background areas to post-injection sessions. Found at: doi:10.1371/journal.pone.0005208.s004 (0.26 MB DOC) Figure S4 Variability of relative saccade direction as a function of the experimental and control session type. Grey background areas correspond to pre-injection sessions; white background areas to post-injection sessions. Found at: doi:10.1371/journal.pone.0005208.s005 (0.26 MB DOC) Figure S5 Log-log plot. (A) Log-log plot of average Lomb- Scargill power spectrum estimates, for response times sequences following GABAA agonist (thick orange line) and GABAA agonist (thin blue line) injections for Monkey A. Frequency f is cycles-per- block. (B) Same convention for monkey B. Found at: doi:10.1371/journal.pone.0005208.s006 (0.91 MB DOC) Figure S6 Variability of response time. (A) Variability of response times as function of experimental session types for monkey C after injection in the right SEF. When the eye movement is produced ipsilaterally (full line box) or contralaterally (dotted line box) to the injection site. (B) same convention as A after injection in the left SEF. (C) same convention as A and B after injection in the Pre-SMA. Found at: doi:10.1371/journal.pone.0005208.s007 (0.39 MB DOC) Author Contributions Conceived and designed the experiments: NW SRp BMG. Performed the experiments: NW SRp BMG. Analyzed the data: PP. Contributed reagents/materials/analysis tools: PP. Wrote the paper: PP BMG. PLoS ONE | www.plosone.org 4 April 2009 | Volume 4 | Issue 4 | e5208