Disconnections in Personal Neglect

Personal neglect is a disorder in the perception and representation of the body that causes the patients to behave as if the contralesional side of their body does not exist. This clinical condition has not been adequately investigated in the past as it has been considered a symptom of unilateral spatial neglect, which has mainly been studied with reference to extrapersonal space. Only a few studies with small samples have investigated the neuroanatomical correlates of personal neglect, and these have mainly focused on discrete cortical lesions and modular accounts, as well as being based on the hypothesis that this disorder is associated with somatosensory and spatial deficits. In the present study, we tested the novel hypothesis that personal neglect may be associated not only with discrete cortical and subcortical lesions, but also with disconnections of white matter tracts. We performed an advanced lesion analyses in a large sample of 104 right hemisphere damaged patients, 68 of whom were suffering from personal neglect. Results from the analyses of the grey and white matter were controlled for co-occurrent clinical variables such as extrapersonal neglect, anosognosia for hemiplegia and motor deficits, along with other lesion-related variables such as lesion size, the interval from the lesion onset to neuroimaging recordings. Our results reveal that personal neglect is associated with lesions in a medial network which involves the temporal cortex (Heschl’s gyrus), the ventro-lateral nuclei of the thalamus, and the fornix. This suggests that personal neglect involves a convergence between sensorimotor processes, spatial representation and the processing of self-referred information (episodic memory).

Sensory-Motor Modulations of EEG Event-Related Potentials Reflect Walking-Related Macro-Affordances

One fundamental principle of the brain functional organization is the elaboration of sensory information for the specification of action plans that are most appropriate for interaction with the environment. Using an incidental go/no-go priming paradigm, we have previously shown a facilitation effect for the execution of a walking-related action in response to far vs. near objects/locations in the extrapersonal space, and this effect has been called “macro-affordance” to reflect the role of locomotion in the coverage of extrapersonal distance. Here, we investigated the neurophysiological underpinnings of such an effect by recording scalp electroencephalography (EEG) from 30 human participants during the same paradigm. The results of a whole-brain analysis indicated a significant modulation of the event-related potentials (ERPs) both during prime and target stimulus presentation. Specifically, consistent with a mechanism of action anticipation and automatic activation of affordances, a stronger ERP was observed in response to prime images framing the environment from a far vs. near distance, and this modulation was localized in dorso-medial motor regions. In addition, an inversion of polarity for far vs. near conditions was observed during the subsequent target period in dorso-medial parietal regions associated with spatially directed foot-related actions. These findings were interpreted within the framework of embodied models of brain functioning as arising from a mechanism of motor-anticipation and subsequent prediction error which was guided by the preferential affordance relationship between the distant large-scale environment and locomotion. More in general, our findings reveal a sensory-motor mechanism for the processing of walking-related environmental affordances.

From embodying tool to embodying alien limb: sensory-motor modulation of personal and extrapersonal space

Years ago, it was demonstrated (e.g., Rizzolatti et al. in Handbook of neuropsychology, Elsevier Science, Amsterdam, 2000) that the brain does not encode the space around us in a homogeneous way, but through neural circuits that map the space relative to the distance that objects of interest have from the body. In monkeys, relatively discrete neural systems, characterized by neurons with specific neurophysiological responses, seem to be dedicated either to represent the space that can be reached by the hand (near/peripersonal space) or to the distant space (far/extrapersonal space). It was also shown that the encoding of spaces has dynamic aspects because they can be remapped by the use of tools that trigger different actions (e.g., Iriki et al. 1998). In this latter case, the effect of the tool depends on the modulation of personal space, that is the space of our body. In this paper, I will review and discuss selected research, which demonstrated that also in humans: 1 spaces are encoded in a dynamic way; 2 encoding can be modulated by the use of tool that the system comes to consider as parts of the own body; 3 body representations are not fixed, but they are fragile and subject to change to the point that we can incorporate not only the tools necessary for action, but even limbs belonging to other people. What embodiment of tools and of alien limb tell us about body representations is then briefly discussed.

VR Setup to Assess Peripersonal Space Audio-Tactile 3D Boundaries

Many distinct spaces surround our bodies. Most schematically, the key division is between peripersonal space (PPS), the close space surrounding our body, and an extrapersonal space, which is the space out of one’s reach. The PPS is considered as an action space, which allows us to interact with our environment by touching and grasping. In the current scientific literature, PPS’ visual representations are appearing as mere bubbles of even dimensions wrapped around the body. Although more recent investigations of PPS’ upper body (trunk, head, and hands) and lower body (legs and foot) have provided new representations, no investigation has been made yet concerning the estimation of PPS’s overall representation in 3D. Previous findings have demonstrated how the relationship between tactile processing and the location of sound sources in space is modified along a spatial continuum. These findings suggest that similar methods can be used to localize the boundaries of the subjective individual representation of PPS. Hence, we designed a behavioral paradigm in virtual reality based on audio-tactile interactions, which has enabled us to infer a detailed individual 3D audio-tactile representation of PPS. Considering that inadequate body-related multisensory integration processes can produce incoherent spatio–temporal perception, the development of a virtual reality setup and a method to estimate the representation of the subjective PPS volumetric boundaries will be a valuable addition for the comprehension of the mismatches occurring between body physical boundaries and body schema representations in 3D.

Functional actions of hands and tools influence attention in peripersonal space

Human perceptual and attentional systems operate to help us perform functional and adaptive actions in the world around us. In this review, we consider different regions of peripersonal space—peri-hand space, reachable space, and tool space when used in both peri- and extrapersonal space. Focusing on behavioural and electrophysiology/event-related potentials (EEG/ERP) studies using comparable target detection paradigms, we examine how visuospatial attention is facilitated or differentiated due to the current proximity and functional capabilities of our hands and the tools we hold in them. The functionality of the hand and tool is defined by the action goals of the user and the available functional affordances or parts available to achieve the goals. Finally, we report recent tool-use studies examining how the distribution of attention to tool space can change as a result of tool functionality and directional action crossing peripersonal and extrapersonal space boundaries. We propose that the functional capabilities of the hand and tools direct attention to action-relevant regions of peripersonal space. Although neural mechanisms such as bimodal neurons may enhance the processing of visual information presented in near-hand regions of peripersonal space, functional experience and the relevance of the space for upcoming actions more strongly direct attention within regions of peripersonal space. And, while some aspects of functionality can be extended into extrapersonal space, the multimodal nature of peripersonal space allows it to be more modifiable in the service of action.

Motor Inhibition to Dangerous Objects: Electrophysiological Evidence for Task-dependent Aversive Affordances

Previous work suggests that perception of an object automatically facilitates actions related to object grasping and manipulation. Recently, the notion of automaticity has been challenged by behavioral studies suggesting that dangerous objects elicit aversive affordances that interfere with encoding of an object's motor properties; however, related EEG studies have provided little support for these claims. We sought EEG evidence that would support the operation of an inhibitory mechanism that interferes with the motor encoding of dangerous objects, and we investigated whether such mechanism would be modulated by the perceived distance of an object and the goal of a given task. EEGs were recorded by 24 participants who passively perceived dangerous and neutral objects in their peripersonal, boundary, or extrapersonal space and performed either a reachability judgment task or a categorization task. Our results showed that greater attention, reflected in the visual P1 potential, was drawn by dangerous and reachable objects. Crucially, a frontal N2 potential, associated with motor inhibition, was larger for dangerous objects only when participants performed a reachability judgment task. Furthermore, a larger parietal P3b potential for dangerous objects indicated the greater difficulty in linking a dangerous object to the appropriate response, especially when it was located in the participants' extrapersonal space. Taken together, our results show that perception of dangerous objects elicits aversive affordances in a task-dependent way and provides evidence for the operation of a neural mechanism that does not code affordances of dangerous objects automatically, but rather on the basis of contextual information.

The monologue of the double: allocentric reduplication of the own voice alters bodily self perception

During autoscopic phenomena, people perceive a double of themselves in extrapersonal space. Such clinical allocentric self-experiences often co-occur with auditory hallucinations, yet experimental setups to induce similar illusions in healthy participants have been limited to visual doubles. We investigated whether feeling the presence of an auditory double could be provoked in healthy participants and how it might affect spatial aspects of bodily self-consciousness. We recorded the own versus another person’s voice while walking around in the room using binaural headphones from an egocentric and an allocentric perspective. In comparison to listening to their own moving voice egocentrically, when listening to themselves allocentrically, participants reported a strong feeling of a presence with a similarly high degree of self-identification, suggesting a successful induction of the feeling of an acoustic doppelganger. When pointing to the source of the own voice participants localized it closer to themselves than when listening to another person’s voice, suggesting a change in spatial perception. Interestingly, the opposite pattern was found in participants that had previous hallucinatory experiences. These findings show that listening to one’s own voice allocentrically can manipulate bodily self-consciousness and self-related spatial perception. This paradigm enables the experimental study of the relationship between auditory vocal hallucinations and bodily self-consciousness, bridging important clinical phenomena and experimental knowledge.

Functional Autonomy Affects Elderly Spatial Perception in Body-Centered Coordinates

According to the action-specific theory of perception, a person’s dynamic ability to act in the environment affects her/his spatial perception. Empirical evidence shows that the elderly perceive distances as farther compared with younger adults and that the harder the ground surface to walk, the farther the perceived distance. Such results suggest a general perceptual readaptation promoted by the aging process that is fine-tuned with the decline of the motor resources. However, it is still unknown whether the elderly space perception is affected by interindividual differences in their functional autonomy (FA) and whether the decline of motor resources affects spatial categorization only when distances are judged with reference to the observer’s own body or also when they are judged with reference to the body of another agent present in the scene. To this aim, a sample of elderly adults with preserved cognitive functions but different levels of FA, measured through the Instrumental Activity of Daily Living (IADL) scale, were enrolled and tested on the extrapersonal space categorization task. This task requires judging the position of a target as “Near” or “Far” with respect to different reference frames (RFs): centered on the observer’s body (Self RF) or centered on external elements, like another body (Other RF) or an object (Object RF). Results indicated that the higher the level of FA, the wider the space categorized as “Near” when adopting as reference frame our own body or the body of another agent in the scene, but not a static object. In conclusion, the individual functional autonomy of elderly individuals, which is strongly influenced by motor resources and efficiency, modulates how the surrounding space is represented, but only when the distance judgment implies an agent body, thus providing new relevant data for recent embodied cognition models of aging.

Modulation of the Somatosensory Blink Reflex in the Peripersonal Space Is Defective in Episodic Migraine

Objective In migraine, there is an altered behavior of patients during the attack and an altered connectivity in the cortical structures modulating and encoding the sensation and pain. Thus, we hypothesized that the extent of the peripersonal space (PPS) and the responses in the PPS may change during a migraine attack. For this reason, we analyzed the modulation of somatosensory blink reflex (SBR) in the PPS during episodic migraine. Design Cross-sectional assessment of modulation of SBR in patients with migraine. Setting Headache outpatient clinic of a tertiary referral center. Subjects We included 22 patients with episodic migraine, of whom 13 individuals were in the interictal period and nine were experiencing a headache episode. We also included 14 healthy individuals. The three groups were similar in age and gender. Methods SBR was recorded when the participants were sitting with their forearm in the extrapersonal space and also when their hands were in the PPS surrounding the face. Latency, amplitude, and area under the curve (AUC) were measured and compared. Results The amplitude and AUC of the SBR were significantly higher in patients during the attack compared with healthy subjects. The magnitude of the SBR was increased in the PPS in healthy subjects, whereas the increase was not significant in patients during the attack or in the interictal period. Conclusions We think that the modulation in the PPS is defective in patients with migraine both during the acute attack and in the interictal phase, suggesting diminished top-down modulation of the SBR.