When humans are engaged in goal-related processing, activity in prefrontal cortex is increased. However, it has remained unclear whether this prefrontal activity encodes a subject's current intention. Instead, increased levels of activity could reflect preparation of motor responses, holding in mind a set of potential choices, tracking the memory of previous responses, or general processes related to establishing a new task set. Here we study subjects who freely decided which of two tasks to perform and covertly held onto an intention during a variable delay. Only after this delay did they perform the chosen task and indicate which task they had prepared. We demonstrate that during the delay, it is possible to decode from activity in medial and lateral regions of prefrontal cortex which of two tasks the subjects were covertly intending to perform. This suggests that covert goals can be represented by distributed patterns of activity in the prefrontal cortex, thereby providing a potential neural substrate for prospective memory. During task execution, most information could be decoded from a more posterior region of prefrontal cortex, suggesting that different brain regions encode goals during task preparation and task execution. Decoding of intentions was most robust from the medial prefrontal cortex, which is consistent with a specific role of this region when subjects reflect on their own mental states.
Left: A spherical searchlight centered on one voxel (vi) was used to define a local neighborhood. For each scanning run, the spatial response pattern in this local spherical cluster was extracted during preparation of either subtraction or addition. We then trained a pattern classifier with a subset of the data to recognize the typical response patterns associated with covert preparation of the two mathematical operations (see Experimental Procedures) and measured the local decoding accuracy. Then, the searchlight was shifted to the next spatial location.
Middle: Highlighted in green are medial brain regions (superimposed on a saggital slice of an anatomical template image) where this local classifier was able to decode significantly above chance which intention the subjects were covertly holding in an independent test data set. Highlighted in red are regions where it was possible to decode the intention during the execution of the task.
Monday, March 26, 2007
Brain imaging can infer your hidden intentions....
As a followup to the 3/14 posting on NeuroLaw, this report from Haynes et al. seems relevant. Here is their abstract, along with a figure from their paper: