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Increased Neural Strength and Reliability to Audiovisual Stimuli at the Boundary of Peripersonal Space
Journal of Cognitive Neuroscience (2019) 31 (8): 1155–1172.
Published: 01 August 2019
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The actionable space surrounding the body, referred to as peripersonal space (PPS), has been the subject of significant interest of late within the broader framework of embodied cognition. Neurophysiological and neuroimaging studies have shown the representation of PPS to be built from visuotactile and audiotactile neurons within a frontoparietal network and whose activity is modulated by the presence of stimuli in proximity to the body. In contrast to single-unit and fMRI studies, an area of inquiry that has received little attention is the EEG characterization associated with PPS processing. Furthermore, although PPS is encoded by multisensory neurons, to date there has been no EEG study systematically examining neural responses to unisensory and multisensory stimuli, as these are presented outside, near, and within the boundary of PPS. Similarly, it remains poorly understood whether multisensory integration is generally more likely at certain spatial locations (e.g., near the body) or whether the cross-modal tactile facilitation that occurs within PPS is simply due to a reduction in the distance between sensory stimuli when close to the body and in line with the spatial principle of multisensory integration. In the current study, to examine the neural dynamics of multisensory processing within and beyond the PPS boundary, we present auditory, visual, and audiovisual stimuli at various distances relative to participants' reaching limit—an approximation of PPS—while recording continuous high-density EEG. We question whether multisensory (vs. unisensory) processing varies as a function of stimulus–observer distance. Results demonstrate a significant increase of global field power (i.e., overall strength of response across the entire electrode montage) for stimuli presented at the PPS boundary—an increase that is largest under multisensory (i.e., audiovisual) conditions. Source localization of the major contributors to this global field power difference suggests neural generators in the intraparietal sulcus and insular cortex, hubs for visuotactile and audiotactile PPS processing. Furthermore, when neural dynamics are examined in more detail, changes in the reliability of evoked potentials in centroparietal electrodes are predictive on a subject-by-subject basis of the later changes in estimated current strength at the intraparietal sulcus linked to stimulus proximity to the PPS boundary. Together, these results provide a previously unrealized view into the neural dynamics and temporal code associated with the encoding of nontactile multisensory around the PPS boundary.
Fronto-parietal Areas Necessary for a Multisensory Representation of Peripersonal Space in Humans: An rTMS Study
Journal of Cognitive Neuroscience (2011) 23 (10): 2956–2967.
Published: 01 October 2011
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A network of brain regions including the ventral premotor cortex (vPMc) and the posterior parietal cortex (PPc) is consistently recruited during processing of multisensory stimuli within peripersonal space (PPS). However, to date, information on the causal role of these fronto-parietal areas in multisensory PPS representation is lacking. Using low-frequency repetitive TMS (rTMS; 1 Hz), we induced transient virtual lesions to the left vPMc, PPc, and visual cortex (V1, control site) and tested whether rTMS affected audio–tactile interaction in the PPS around the hand. Subjects performed a timed response task to a tactile stimulus on their right (contralateral to rTMS) hand while concurrent task-irrelevant sounds were presented either close to the hand or 1 m far from the hand. When no rTMS was delivered, a sound close to the hand reduced RT-to-tactile targets as compared with when a far sound was presented. This space-dependent, auditory modulation of tactile perception was specific to a hand-centered reference frame. Such a specific form of multisensory interaction near the hand can be taken as a behavioral hallmark of PPS representation. Crucially, virtual lesions to vPMc and PPc, but not to V1, eliminated the speeding effect due to near sounds, showing a disruption of audio–tactile interactions around the hand. These findings indicate that multisensory interaction around the hand depends on the functions of vPMc and PPc, thus pointing to the necessity of this human fronto-parietal network in multisensory representation of PPS.
Journal of Cognitive Neuroscience (2011) 23 (3): 503–513.
Published: 01 March 2011
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The perception of tactile stimuli on the face is modulated if subjects concurrently observe a face being touched; this effect, termed visual remapping of touch (VRT), is maximum for observing one's own face. In the present fMRI study, we investigated the neural basis of the VRT effect. Participants in the scanner received tactile stimuli, near the perceptual threshold, on their right, left, or both cheeks. Concurrently, they watched movies depicting their own face, another person's face, or a ball that could be touched or only approached by human fingers. Participants were requested to distinguish between unilateral and bilateral tactile stimulation. Behaviorally, perception of tactile stimuli was modulated by viewing a tactile stimulation, with a stronger effect when viewing one's own face being touched. In terms of brain activity, viewing touch was related with an enhanced activity in the ventral intraparietal area. The specific effect of viewing touch on oneself was instead related with a reduced activity in both the ventral premotor cortex and the somatosensory cortex. The present findings suggest that VRT is supported by a network of fronto-parietal areas. The ventral intraparietal area might remap visual information about touch onto tactile processing. Ventral premotor cortex might specifically modulate multisensory interaction when sensory information is related to one's own body. Then this activity might back project to the somatosensory cortices, thus affecting tactile perception.
Journal of Cognitive Neuroscience (2010) 22 (3): 413–426.
Published: 01 March 2010
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Several studies have shown that the motor system is involved in action perception, suggesting that action concepts are represented through sensory–motor processes. Such conclusions imply that motor system impairments should diminish action perception. To test this hypothesis, a group of 10 brain-damaged patients with hemiplegia (specifically, a lesion at the motor system that affected the contralesional arm) viewed point-light displays of arm gestures and attempted to name each gesture. To create the dynamic stimuli, patients individually performed simple gestures with their unaffected arm while being videotaped. The videotapes were converted into point-light animations. Each action was presented as it had been performed, that is, as having been produced by the observer's unaffected arm, and in its mirror reversed orientation, that is, as having been produced by the observer's hemiplegic arm. Action recognition accuracy by patients with hemiplegia was compared with that by 8 brain-damaged patients without any motor deficit and by 10 healthy controls. Overall, performance was better in control observers than in patients. Most importantly, performance by hemiplegic patients, but not by nonhemiplegic patients and controls, varied systematically as a function of the observed limb. Action recognition was best when hemiplegic patients viewed actions that appeared to have been performed by their unaffected arm. Action recognition performance dropped significantly when hemiplegic patients viewed actions that appeared to have been produced with their hemiplegic arm or the corresponding arm of another person. The results of a control study involving the recognition of point-light defined animals in motion indicate that a generic deficit to visual and cognitive functions cannot account for this laterality-specific deficit in action recognition. Taken together, these results suggest that motor cortex impairment decreases visual sensitivity to human action. Specifically, when a cortical lesion renders an observer incapable of performing an observed action, action perception is compromised, possibly by a failure to map the observed action onto the observer's contralesional hemisoma.