Domain general mechanisms of perceptual decision making in human cortex

To successfully interact with objects in the environment, sensory evidence must be continuously acquired, interpreted, and used to guide appropriate motor responses. For example, when driving, a red light should motivate a motor command to depress the brake pedal. Single-unit recording studies have established that simple sensorimotor transformations are mediated by the same neurons that ultimately guide the behavioral response. However, it is also possible that these sensorimotor regions are the recipients of a modality-independent decision signal that is computed elsewhere. Here, we used functional magnetic resonance imaging and human observers to show that the time course of activation in a subregion of the right insula is consistent with a role in accumulating sensory evidence independently from the required motor response modality (saccade vs manual). Furthermore, a combination of computational modeling and simulations of the blood oxygenation level-dependent response suggests that this region is not simply recruited by general arousal or by the tonic maintenance of attention during the decision process. Our data thus raise the possibility that a modality-independent representation of sensory evidence may guide activity in effector-specific cortical areas before the initiation of a behavioral response.