These results suggest a facilitatory effect of microstimulation on contraversive saccades. In contrast, when delivered before saccade onset at “blindly” sampled sites, caudate microstimulation increases RT for contraversive saccades and, to a lesser extent,

decreases RT for ipsiversive saccades on a pro-/antisaccade task (Watanabe and Munoz, 2010, 2011). These results suggest a suppressive effect of microstimulation on contraversive saccades. In light of our observations, these previous reports may have resulted from Selleckchem PI3K Inhibitor Library differential activation of distinct functional groups of neurons. More specifically, microstimulation that preferentially activates neurons participating in saccade generation facilitates generation of contraversive saccades. In contrast, microstimulation that preferentially

activates neurons participating in perceptual-decision formation or other cognitively demanding forms of saccade selection facilitates selection of ipsilateral saccade targets. The former effect dominates for evoked saccades and for simple saccade tasks with targeted microstimulation sites. Both effects are in place for pro-/antisaccade tasks with blindly sampled microstimulation sites and for the dots task. The dots task enables the dissociation of perceptual decision-making and saccade effects, with manipulations of stimulus strength (Petrov et al., 2011). In contrast to the microstimulation find more effects on choice bias, we did not observe a consistent effect on discrimination threshold. This result is consistent with our interpretation of caudate

Tolmetin response properties in the context of the DDM (Ding and Gold, 2010). According to that framework, discrimination threshold is determined by the decision bounds and a constant of proportionality used to convert the evidence to a log likelihood ratio-related quantity (Gold and Shadlen, 2002; Ratcliff, 1978). The decision bounds govern the speed-accuracy tradeoff and in our previous study were not encoded in caudate: unlike in LIP and FEF, evidence-accumulation activity in caudate did not converge at a DDM-like bound just prior to saccade onset on the RT dots task (Ding and Gold, 2010, 2012; Roitman and Shadlen, 2002). The constant of proportionality may already be incorporated in the inputs from MT and thus not influenced by caudate microstimulation. However, despite this consistency with our previous recording study, the lack of an effect on discrimination threshold is not consistent with previous computational modeling and fMRI studies that posit a role for the basal ganglia pathway in mediating the appropriate speed-accuracy tradeoff (Bogacz et al., 2010; Brown et al., 2004; Forstmann et al., 2008; Frank, 2006; Gurney et al., 2004; Lo and Wang, 2006; Rao, 2010; van Veen et al., 2008). This discrepancy might reflect a sampling bias in the present study favoring sites with the kind of task-modulated neural activity we described previously.