ORIGINAL RESEARCH ARTICLE

In addition, studies on motor preparation have shown that the instruction to later execute a particular movement results in increased activation of brain areas such as dorsal pre-motor cortex (PMd) and primary motor cortex (M1) (Riehle and Requin, 1989; Toni et al., 1999; Crammond and Kalaska, 2000; Cisek et al., 2003; Zang et al., 2003; Churchland et al., 2006). Instruction-related changes in activation have also been found in the thalamus (Michelon et al., 2006), the supplementary motor area (SMA), the anterior cingulate cortex (ACC; Nagai et al., 2004), orbitofrontal cortex (OFC; Ikeda et al., 1996), and the putamen (Alexander and Crutcher, 1990; Jaeger et al., 1993). Interestingly, single-cell recordings showed that cortical activation precedes activation in the putamen, suggesting that the preparatory activity in the putamen might be caused by input from M1 and SMA (Alexander and Crutcher, 1990; Mink, 1996). Here we present an functional magnetic resonance imaging (fMRI) study in people were given cues that provided probabilis-tic information about the direction of movement of an upcoming random dot display (i.e., 90%, 70%, or 50 % valid). At a behavioral level, we anticipated that the effect of this manipulation would be to bias people’s decision criteria, a prediction that we verifi ed by fi tting a quantitative model to the behavioral data. At a neural level, we anticipated that the effect of the manipulation would be to acti-vate subcortical, striatal areas involved in motor planning and action preparation (Mink, 1996; Draganski et al., 2008; Utter and Basso, 2008). In addition, we anticipated that this striatal activation would be accompanied by activation in cortical control areas such as DLPF