Sharpening of peripersonal space during the COVID-19 pandemic.

Our social world has been transformed by the COVID-19 pandemic. Beyond the direct impact of the pandemic on physical health, the social distancing measures implemented worldwide to slow down disease transmission have dramatically impacted social interactions1,2. These measures, including orders to stay at home and to maintain a social distance of at least 2 meters, have been essential to limit the spread of the disease, but they have had severe costs for humans as social animals2. Right before and right after the adoption of the most stringent measures in Switzerland in Spring 2020, we were conducting a series of experiments to measure the representation of the so-called peripersonal space - the space immediately surrounding our body, where we normally interact with objects and other individuals3. We found that the introduction of social distancing measures led to a reduction in the extent of the peripersonal space and enhanced its segregation between individuals, as if the presence of others in close space would activate an implicit form of freezing response.

Common Recruitment of Angular Gyrus in Episodic Autobiographical Memory and Bodily Self-Consciousness.

Parietal cortex and adjacent parts of the temporal cortex have recently been associated with bodily self-consciousness (BSC). Similarly, growing evidence suggests that the lateral parietal cortex is crucial for the subjective aspects of episodic autobiographical memory (EAM), which is based on the conscious experience of reliving past events. However, the neuroanatomical relationship between both fundamental aspects remains currently unexplored. Moreover, despite the wealth of neuroimaging data on EAM, only few neuroimaging studies have examined BSC and even fewer examined those aspects of BSC that are most closely related to EAM. Here, we investigated whether regions in the inferior parietal lobule (IPL) that have been involved in spatial aspects of BSC (self-location and first-person perspective), as described by Ionta et al. (2011) are also active in studies investigating autobiographical memory. To examine this relation, we thus compared the regions indicated in the study by Ionta et al. (2011) based on data in healthy participants and neurological patients, with the results from a meta-analytical study we performed based on functional neuroimaging studies on EAM and semantic autobiographical memory (SAM). We report an anatomical overlap bilaterally in the angular gyrus (AG), but not in other parietal or temporal lobe structures between BSC and EAM. Moreover, there was no overlap between BSC and SAM. These preliminary data suggest that the bilateral AG may be a key structure for the conscious re-experiencing of past life episodes (EAM) and the conscious on-line experience of being located and experiencing the world in first-person (BSC).

Cognitive Deficits in Multiple Sclerosis: Recent Advances in Treatment and Neurorehabilitation.

PURPOSE OF REVIEW: This article highlights recent progress in research on treatment and neurorehabilitation of cognitive impairment in multiple sclerosis (MS) including pharmacological interventions, physical exercise, and neuropsychological rehabilitation, both in conventional and technology-assisted settings. RECENT FINDINGS: The most consistent evidence in terms of improvement or preservation of circumscribed cognitive scores in MS patients comes from moderately sampled randomized clinical trials on multimodal approaches that combine conventional or computerized neuropsychological training with psychoeducation or cognitive behavioral therapy. Disease-modifying treatments also appear to have beneficial effects in preventing or attenuating cognitive decline, whereas there is little evidence for agents such as donepezil or stimulants. Finally, physical exercise may yield some cognitive improvement in MS patients. Despite substantial and often promising research efforts, there is a lack of validated and widely accepted clinical procedures for cognitive neurorehabilitation in MS. Development of such approaches will require collaborative efforts towards the design of interventions that are fundamentally inspired by cognitive neuroscience, potentially guided by neuroimaging, and composed of conventional neuropsychological training and cognitive behavioral therapy as well as physical exercise and therapeutic video games. Subsequently, large-scale validation will be needed with meaningful outcome measures reflecting transfer to everyday cognitive function and maintenance of training effects.

Common and distinct brain regions processing multisensory bodily signals for peripersonal space and body ownership.

We take the feeling that our body belongs to us for granted. However, recent research has shown that it is possible to alter the subjective sensation of body ownership (BO) by manipulating multisensory bodily inputs. Several frontal and parietal regions are known to specifically process multisensory cues presented close to the body, i.e., within the peripersonal space (PPS). It has been proposed that these PPS fronto-parietal regions also underlie BO. However, most previous studies investigated the brain mechanisms of either BO or of PPS processing separately and by using a variety of paradigms. Here, we conducted an extensive meta-analysis of functional neuroimaging studies to investigate PPS and BO processing in humans in order to: a) assess quantitatively where each one of these functions was individually processed in the brain; b) identify whether and where these processes shared common or engaged distinct brain mechanisms; c) characterize these areas in terms of whole-brain co-activation networks and functions, respectively. We identified (i) a bilateral PPS network including superior parietal, temporo-parietal and ventral premotor regions and (ii) a BO network including posterior parietal cortex (right intraparietal sulcus, IPS; and left IPS and superior parietal lobule, SPL), right ventral premotor cortex, and the left anterior insula. Co-activation maps related to both PPS and BO encompassed largely overlapping fronto-parietal networks, but whereas the PPS network was more frequently associated with sensorimotor tasks, the BO network was rather associated with attention and awareness tasks. Finally, the conjunction analysis showed that (iii) PPS and BO tasks anatomically overlapped only in two clusters located in the left parietal cortex (dorsally at the intersection between the SPL, the IPS and area 2 and ventrally between areas 2 and IPS). Distinct activations were located for PPS at the temporo-parietal junction and for BO in the anterior insula. These results in PPS and BO and provide evidence-based insight about the overlap of the two processes in the IPS region and the extensive connectivity between the two associated co-activation networks. They also show significant dissociations, with PPS fronto-parietal areas located more proximal to the central sulcus than BO areas. Such anatomical distinction may also reflect the different functions of the two processes, whereby PPS areas underlie a multisensory-motor interface for body-objects interaction and BO areas being involved in bodily awareness and self-consciousness.

Visual gravity contributes to subjective first-person perspective.

A fundamental component of conscious experience involves a first-person perspective (1PP), characterized by the experience of being a subject and of being directed at the world. Extending earlier work on multisensory perceptual mechanisms of 1PP, we here asked whether the experienced direction of the 1PP (i.e. the spatial direction of subjective experience of the world) depends on visual-tactile-vestibular conflicts, including the direction of gravity. Sixteen healthy subjects in supine position received visuo-tactile synchronous or asynchronous stroking to induce a full-body illusion. In the critical manipulation, we presented gravitational visual object motion directed toward or away from the participant's body and thus congruent or incongruent with respect to the direction of vestibular and somatosensory gravitational cues. The results showed that multisensory gravitational conflict induced within-subject changes of the experienced direction of the 1PP that depended on the direction of visual gravitational cues. Participants experienced more often a downward direction of their 1PP (incongruent with respect to the participant's physical body posture) when visual object motion was directed away rather than towards the participant's body. These downward-directed 1PP experiences positively correlated with measures of elevated self-location. Together, these results show that visual gravitational cues contribute to the experienced direction of the 1PP, defining the subjective location and perspective from where humans experience to perceive the world.

Out-of-Body Experiences and Other Complex Dissociation Experiences in a Patient with Unilateral Peripheral Vestibular Damage and Deficient Multisensory Integration.

Out-of-body experiences (OBEs) are illusory perceptions of one's body from an elevated disembodied perspective. Recent theories postulate a double disintegration process in the personal (visual, proprioceptive and tactile disintegration) and extrapersonal (visual and vestibular disintegration) space as the basis of OBEs. Here we describe a case which corroborates and extends this hypothesis. The patient suffered from peripheral vestibular damage and presented with OBEs and lucid dreams. Analysis of the patient's behaviour revealed a failure of visuo-vestibular integration and abnormal sensitivity to visuo-tactile conflicts that have previously been shown to experimentally induce out-of-body illusions (in healthy subjects). In light of these experimental findings and the patient's symptomatology we extend an earlier model of the role of vestibular signals in OBEs. Our results advocate the involvement of subcortical bodily mechanisms in the occurrence of OBEs.

Full body action remapping of peripersonal space: the case of walking.

The space immediately surrounding the body, i.e. peripersonal space (PPS), is represented by populations of multisensory neurons, from a network of premotor and parietal areas, which integrate tactile stimuli from the body's surface with visual or auditory stimuli presented within a limited distance from the body. Here we show that PPS boundaries extend while walking. We used an audio-tactile interaction task to identify the location in space where looming sounds affect reaction time to tactile stimuli on the chest, taken as a proxy of the PPS boundary. The task was administered while participants either stood still or walked on a treadmill. In addition, in two separate experiments, subjects either received or not additional visual inputs, i.e. optic flow, implying a translation congruent with the direction of their walking. Results revealed that when participants were standing still, sounds boosted tactile processing when located within 65-100 cm from the participants' body, but not at farther distances. Instead, when participants were walking PPS expands as reflected in boosted tactile processing at ~1.66 m. This was found despite the fact the spatial relationship between the participant's body and the sound's source did not vary between the Standing and the Walking condition. This expansion effect on PPS boundaries due to walking was the same with or without optic flow, suggesting that kinematics and proprioceptive cues, rather than visual cues, are critical in triggering the effect. These results are the first to demonstrate an adaptation of the chest's PPS representation due to whole body motion and are compatible with the view that PPS constitutes a dynamic sensory-motor interface between the individual and the environment.