Reading Hidden Intentions in the Human Brain

...We recorded brain responses with functional magnetic resonance imaging at 3 Tesla while subjects were performing the free-selection task. In order to investigate which cortical regions encode the subject's current intention, we next assessed whether it was possible to decode from the spatial pattern of signals in each local region of the brain which intention the subject was covertly maintaining 11, 12, 13 and 14. For this, we applied multivariate pattern recognition to spatial patterns of brain responses under the two possible intentions (see Experimental Procedures and Figure 2 for details on this analysis). We found that indeed several regions predicted whether the subject was currently covertly intending to perform the addition or subtraction task (Figure 2). The highest decoding accuracy of 71% was achieved in medial prefrontal cortex (T[7] = 4.62, p = 0.001, see Figure 2, “MPFCa”). Importantly, however, decoding in this region was not possible during task execution, suggesting that the intention was encoded in this brain region only during the delay and not during task execution. In contrast, a region more superior and posterior along the medial wall was not informative during the delay, but only during the execution of the freely chosen task (Figure 2, “MPFCp”). Besides medial prefrontal cortex, there were also several regions of lateral prefrontal cortex where decoding accuracy was lower, but still above chance level (Figure 2). Also in these regions, decoding was at chance level during task execution. Interestingly, only a region of anterior-medial prefrontal cortex showed an overall increase of activity during the delay period while subjects had covertly formed a decision but were still waiting to execute the task (Figure S2). As in previous studies 10 and 15, the duration of increased neural activity corresponded to the delay in the current task, with longer delays leading to longer fMRI responses. However, this region with an overall signal increase was more anterior to the region that encoded the subject's intentions. Importantly, there was no difference between the two intentions in the overall level of activity (T[7] = −0.46; p = 0.67) in medial prefrontal cortex, suggesting that the intentions were not encoded in different global levels of activity but in the detailed spatial patterns of cortical responses.