The neural consequences of conflict between intention and the senses

Normal sensorimotor states involve integration of intention, action and sen sory feedback. An example is the congruence between motor intention and sen sory experience (both proprioceptive and visual) when we move a limb throug h space, Such goal-directed action necessitates a mechanism that monitors s ensorimotor inputs to ensure that motor outputs are congruent with current intentions. Monitoring in this sense is usually implicit and automatic but becomes conscious whenever there is a mismatch between expected and realize d sensorimotor states. To investigate how the latter type of monitoring is achieved we conducted three fully factorial functional neuroimaging experim ents using PET measures of relative regional cerebral blood flow with healt hy volunteers. In the first experiment subjects were asked to perform Luria 's bimanual co-ordination task which involves either in-phase (conditions 1 and 3) or out-of-phase (conditions 2 and 4) bimanual movements (factor one ), while looking towards their left hand. In half of the conditions (condit ions 3 and 4) a mirror was used that altered visual feedback (factor two) b y replacing their left hand with the mirror image of their right hand. Henc e (in the critical condition 4) subjects saw in-phase movements despite per forming out-of-phase movements. This mismatch between intention, propriocep tion and visual feedback engendered cognitive conflict, The main effect of out-of-phase movements was associated with increased neural activity in pos terior parietal cortex (PPC) bilaterally [Brodmann area (BA) 40, extending into BA 7] and dorsolateral prefrontal cortex (DLPFC) bilaterally (BA 9/46) . The main effect of the mirror showed increased neural activity in right D LPFC (BA 9/46) and right superior PPC (BA 7) only, Analysis of the critical interaction revealed that the mismatch condition led to a specific activat ion in the right DLPFC alone (BA 9/46). Study 2, using an identical experim ental setup but manipulating visual feedback from the right hand (instead o f the left), subsequently demonstrated that this right DLPFC activation was independent of the hand attended. Finally, study 3 removed the motor inten tional component by moving the subjects' hand passively, thus engendering a mismatch between proprioception and vision only. Activation in the right l ateral prefrontal cortex was now more ventral than in studies 1 or 2 (BA 44 /45). A direct comparison of studies 1 and 3 (which both manipulated visual feedback from the left hand) confirmed that a ventral right lateral prefro ntal region is primarily activated by discrepancies between signals from se nsory systems, while a more dorsal area in right lateral prefrontal cortex is activated when actions must be maintained in the face of a conflict betw een intention and sensory outcome.