Reorganisation of the Right Occipito-Parietal Stream for Auditory Spatial Processing in Early Blind Humans. A Transcranial Magnetic Stimulation Study

Abstract

It is well known that, following an early visual deprivation, the neural network involved in processing auditory spatial information undergoes a profound reorganization. In particular, several studies have demonstrated an extensive activation of occipital brain areas, usually regarded as essentially "visual", when early blind subjects (EB) performed a task that requires spatial processing of sounds. However, little is known about the possible consequences of the activation of occipitals area on the function of the large cortical network known, in sighted subjects, to be involved in the processing of auditory spatial information. To address this issue, we used event-related transcranial magnetic stimulation (TMS) to induce virtual lesions of either the right intra-parietal sulcus (rIPS) or the right dorsal extrastriate occipital cortex (rOC) at different delays in EB subjects performing a sound lateralization task. Surprisingly, TMS applied over rIPS, a region critically involved in the spatial processing of sound in sighted subjects, had no influence on the task performance in EB. In contrast, TMS applied over rOC 50 ms after sound onset, disrupted the spatial processing of sounds originating from the contralateral hemifield. The present study shed new lights on the reorganisation of the cortical network dedicated to the spatial processing of sounds in EB by showing an early contribution of rOC and a lesser involvement of rIPS.

Language processing in the occipital cortex of congenitally blind adults

“…The response to language is strongly left lateralized. By contrast, responses during nonverbal tasks are bilateral or right lateralized (44,45). Consistent with this idea, we found neuroanatomically distinct patterns of response to backward speech and language in the occipital cortex.…”

Impact of blindness onset on the functional organization and the connectivity of the occipital cortex

“…Importantly, these plastic changes appear to be compensatory in nature because they have been shown to correlate with improved abilities in the remaining senses (Amedi et al, 2003;Gougoux et al, 2005). This conclusion is further supported by studies showing that the transient disruption of occipital activity induced by transcranial magnetic stimulation impairs non-visual functions of congenitally blind individuals (Cohen et al, 1997;Amedi et al, 2004;Collignon et al, 2007Collignon et al, , 2009a.…”

“…A sensitive period for the development of functionally specific crossmodal reorganization for auditory spatial processing in the occipital cortex of blind individuals It was recently demonstrated that non-visual recruitment of the occipital cortex follows organizational principles that maintain the functional specialization of the colonized brain regions (Collignon et al, 2009a;Ricciardi and Pietrini, 2011;Reich et al, 2012). This suggests that a specialized region that evolved to perform a specific cognitive operation (i.e.…”

Spatial Remapping in the Audio-tactile Ventriloquism Effect: A TMS Investigation on the Role of the Ventral Intraparietal Area

“…In Experiment 1, SI was selected as a control site assuming that, by avoiding the hand representation within the somatosensory cortex (Collignon et al, 2008(Collignon et al, , 2009Lotze et al, 2003), TMS to this area would not affect performance. To exclude the possibility that SI stimulation affected either unimodal or bimodal task performance, we ran a second experiment with both sham TMS (obtained by tilting the coil 180°) to the left and right hVIP and no TMS at all.…”

“…We preferred this approach compared with, for example, a stimulation of the vertex, to control for the lateralization of possible unspecific effects of TMS (e.g., auditory clicks) on auditory performance, on the basis of previous studies involving auditory stimuli (see Collignon, Davare, Olivier, & De Volder, 2009;Collignon et al, 2008), and on our own pilot testing. The x coordinate of SI was set to avoid stimulating the hand representation of the somatosensory cortex (Lotze et al, 2003; see also Collignon et al, 2008Collignon et al, , 2009.…”