The cortical eye proprioceptive signal modulates neural activity in higher-order visual cortex as predicted by the variation in visual sensitivity

Whereas the links between eye movements and the shifts in visual attention are well established, less is known about how eye position affects the prioritization of visual space. It was recently observed that visual sensitivity varies with the direction of gaze and the level of excitability in the eye proprioceptive representation in human left somatosensory cortex (S1(EYE)), so that after 1 Hz repetitive transcranial magnetic stimulation (rTMS) over S1(EYE), targets presented nearer the center of the orbit are detected more accurately. Here we used whole-brain functional magnetic resonance imaging to map areas where S1(EYE)-rTMS affects the neural response evoked by retinally identical stimuli depending on the direction of rotation of the right eye. After S1(EYE)-rTMS, a single area in the left cuneus outside Brodmann Areas 17/18 showed an increased neuronal response to a right hemifield target when the right eye was rotated leftwards as compared with when it was rotated rightwards. This effect was larger after S1(EYE)-rTMS than after rTMS of a control area in the motor cortex. The neural response to retinally identical stimuli in this area could be predicted from the changes in visual detectability observed previously, but not from the location of the visual targets relative to the body. These results strongly argue for a modulatory connection from the eye proprioceptive area in the somatosensory cortex to the higher-order visual cortex. This connection may contribute to flexibly allocate priorities for visual perception depending on the proprioceptively signaled direction of gaze. (C) 2012 Elsevier Inc. All rights reserved.</p

Short-term plasticity of visuo-haptic object recognition

Functional magnetic resonance imaging (fMRI) studies have provided ample evidence for the involvement of the lateral occipital cortex (LO), fusiform gyrus (FG), and intraparietal sulcus (IPS) in visuo-haptic object integration. Here we applied 30 min of sham (non-effective) or real offline 1 Hz repetitive transcranial magnetic stimulation (rTMS) to perturb neural processing in left LO immediately before subjects performed a visuo-haptic delayed-match-to-sample task during fMRI. In this task, subjects had to match sample (S1) and target (S2) objects presented sequentially within or across vision and/or haptics in both directions (visual-haptic or haptic-visual) and decide whether or not S1 and S2 were the same objects. Real rTMS transiently decreased activity at the site of stimulation and remote regions such as the right LO and bilateral FG during haptic S1 processing. Without affecting behavior, the same stimulation gave rise to relative increases in activation during S2 processing in the right LO, left FG, bilateral IPS, and other regions previously associated with object recognition. Critically, the modality of S2 determined which regions were recruited after rTMS. Relative to sham rTMS, real rTMS induced increased activations during crossmodal congruent matching in the left FG for haptic S2 and the temporal pole for visual S2. In addition, we found stronger activations for incongruent than congruent matching in the right anterior parahippocampus and middle frontal gyrus for crossmodal matching of haptic S2 and in the left FG and bilateral IPS for unimodal matching of visual S2, only after real but not sham rTMS. The results imply that a focal perturbation of the left LO triggers modality-specific interactions between the stimulated left LO and other key regions of object processing possibly to maintain unimpaired object recognition. This suggests that visual and haptic processing engage partially distinct brain networks during visuo-haptic object matching