Fig. 2.

Coherence and Granger causality between cortex and the nucleus accumbens during the decision-making task. A: schematic of 1 trial of the task with distinct task stages (all intervals are equal to 1.5 s in duration). ITI, intertrial interval. B: coherence as a function of frequency during all 4 stages of the task, color-coded as in A (black, baseline/ITI; red, decision stage; green, anticipation stage; blue, outcome stage). Coherence is significantly enhanced during the decision stage compared with baseline in 3 patients (P2, P3, and P6). Numbers next to peaks correspond to peak frequencies. Each row shows data for 1 of the 5 patients (P1 to P6). C: Granger causality spectra for the decision stage of the task. As in Fig. 1C, the left column shows a Granger causal influence of cortex on the nucleus accumbens, whereas the right column shows coupling in the opposite direction (nucleus accumbens leading cortex). The dotted line shows Granger causality after the time axis is reversed at all channels. The gray vertical shading indicates frequency bins at which the original spectrum (black line) is significantly greater than the spectrum computed after the time axis is reversed. Four of the 5 patients show a significant cortical drive of delta oscillations in the nucleus accumbens (trend in P3).