Disruption of the prefrontal cortex function by rTMS produces a category-specific enhancement of the reaction times during visual object identification

Object identification is enabled through a distributed neural network but the relative contribution of the single components of this network is largely unknown. In the present study, we used online interference by repetitive transcranial magnetic stimulation (rTMS) to investigate the role of the dorso-lateral prefrontal cortex (DLPFC) in identifying semantically different stimuli presented as to make the decision process easy or difficult, according to the amount of sensory information available. Nineteen healthy volunteers performed an object identification task. Stimuli belonging to living and non-living categories were presented at different levels of spatial filtering following a coarse-to-fine order that gradually integrated spatial information. Six-pulse trains of 10-Hz rTMS were delivered at an intensity of 90% resting motor threshold simultaneously to the picture presentation. rTMS of either the left or right DLPFC produced a significant lengthening in the identification process of spatially filtered living stimuli, as shown by the increase in the reaction time, but not of non-filtered living stimuli or of non-living objects. rTMS over the vertex did not interfere with the identification task. These data indicate that DLPFC role in the network underlying object recognition is more crucial when this neural process is challenged by the level of sensory information available to the observer. Specificity of this effect for living objects is discussed taking into account the crucial role of DLPFC in recruitment of cognitive resources for accomplishing perceptual decision-making.