P215 Disentangling rule-dependent from stimulus-dependent brain networks in the action observation domain by means of combined TMS and fMRI

Abstract

Introduction The ability to perform appropriate behavior in response to others’ actions is a building block of social interactions. Two components concur in such capacity: an imitative pattern of behavior, based on parieto-frontal circuitry, and a non-imitative modality. Objective In this experiment we investigate the neural substrates of the capacity to override imitative tendencies and perform non-imitative behavior. Materials and methods In a first, localizer experiment, We challenged healthy human participants in an imitative (i.e. stimulus dependent) and a non-imitative (i.e. rule-dependent) task while undergoing functional magnetic resonance imaging (fMRI). A complex cortical network comprising the ventral prefrontal, the premotor, parietal, superior temporal and lateral occipital cortices showed increased activation during non-imitative, compared to imitative behavior. In a second experiment we applied 20 min of 1 Hz repetitive transcranial magnetic stimulation (rTMS) to the left ventral prefrontal cortex as indicated by experiment 1, and immediately after underwent fMRI while performing the imitative and the non-imitative tasks. Results We observed that differences in blood-oxygen-level-dependent (BOLD) signal between the two tasks were significantly modulated by the prior application of rTMS to the prefrontal cortex. Sites showing such rTMS*task interactions in BOLD signal included the ventral and anterior prefrontal cortex, the parietal and premotor regions bilaterally, the pre-supplementary motor area, the posterior superior temporal cortex. Conclusion Local modulation of neural activity in the prefrontal cortex by rTMS generated a cascade of events in a cortical network that is likely to support our capacity to perform flexible non-imitative behavior.