Frontal and parietal background connectivity and their dynamic changes account for individual differences in the multisensory representation of peripersonal space

Individual Differences in Bodily Self-Consciousness and Its Neural Basis

Bodily self-consciousness (BSC), a subject of interdisciplinary interest, refers to the awareness of one's bodily states. Previous studies have noted the existence of individual differences in BSC, while neglecting the underlying factors and neural basis of such individual differences. Considering that BSC relied on integration from both internal and external self-relevant information, we here review previous findings on individual differences in BSC through a three-level-self model, which includes interoceptive, exteroceptive, and mental self-processing. The data show that cross-level factors influenced individual differences in BSC, involving internal bodily signal perceptibility, multisensory processing principles, personal traits shaped by environment, and interaction modes that integrate multiple levels of self-processing. Furthermore, in interoceptive processing, regions like the anterior cingulate cortex and insula show correlations with different perceptions of internal sensations. For exteroception, the parietal lobe integrates sensory inputs, coordinating various BSC responses. Mental self-processing modulates differences in BSC through areas like the medial prefrontal cortex. For interactions between multiple levels of self-processing, regions like the intraparietal sulcus involve individual differences in BSC. We propose that diverse experiences of BSC can be attributed to different levels of self-processing, which moderates one's perception of their body. Overall, considering individual differences in BSC is worth amalgamating diverse methodologies for the diagnosis and treatment of some diseases.

Dynamic brain states in spatial neglect after stroke

Previous studies indicated that spatial neglect is characterized by widespread alteration of resting-state functional connectivity and changes in the functional topology of large-scale brain systems. However, whether such network modulations exhibit temporal fluctuations related to spatial neglect is still largely unknown. This study investigated the association between brain states and spatial neglect after the onset of focal brain lesions. A cohort of right-hemisphere stroke patients (n = 20) underwent neuropsychological assessment of neglect as well as structural and resting-state functional MRI sessions within 2 weeks from stroke onset. Brain states were identified using dynamic functional connectivity as estimated by the sliding window approach followed by clustering of seven resting state networks. The networks included visual, dorsal attention, sensorimotor, cingulo-opercular, language, fronto-parietal, and default mode networks. The analyses on the whole cohort of patients, i.e., with and without neglect, identified two distinct brain states characterized by different degrees of brain modularity and system segregation. Compared to non-neglect patients, neglect subjects spent more time in less modular and segregated state characterized by weak intra-network coupling and sparse inter-network interactions. By contrast, patients without neglect dwelt mainly in more modular and segregated states, which displayed robust intra-network connectivity and anti-correlations among task-positive and task-negative systems. Notably, correlational analyses indicated that patients exhibiting more severe neglect spent more time and dwelt more often in the state featuring low brain modularity and system segregation and vice versa. Furthermore, separate analyses on neglect vs. non-neglect patients yielded two distinct brain states for each sub-cohort. A state featuring widespread strong connections within and between networks and low modularity and system segregation was detected only in the neglect group. Such a connectivity profile blurred the distinction among functional systems. Finally, a state exhibiting a clear separation among modules with strong positive intra-network and negative inter-network connectivity was found only in the non-neglect group. Overall, our results indicate that stroke yielding spatial attention deficits affects the time-varying properties of functional interactions among large-scale networks. These findings provide further insights into the pathophysiology of spatial neglect and its treatment.

Touching you, touching me: Higher incidence of mirror-touch synaesthesia and positive (but not negative) reactions to social touch in Autonomous Sensory Meridian Response

The characterisation of autonomous sensory meridian response (ASMR) as an audio-visual phenomenon overlooks how tactile experiences are not just perceptual concurrents of ASMR (i.e., tingling) but also commonly strong ASMR inducers. Here we systematically investigated whether ASMR-responders show altered tactile processing compared to controls. Using a screening measure of vicarious touch with a predefined cut-off for mirror-touch synaesthesia (MTS; a condition where tactile sensations are experienced when viewing, but not receiving, touch), we found that ASMR-responders had more frequent and intense vicarious touch experiences, as well as a strikingly higher incidence of MTS, than non-responders. ASMR-responders also reported greater reactivity to positive, but not negative, interpersonal touch. Correlations further showed these patterns to be more prevalent in those responders with stronger ASMR. We discuss the implications of our findings in terms of heightened sensory sensitivity, bodily awareness, and the underlying neuro-cognitive mechanisms driving vicarious tactile perception in ASMR and MTS.

Tool-use Extends Peripersonal Space Boundaries in Schizophrenic Patients

BACKGROUND AND HYPOTHESIS

A primary disruption of the bodily self is considered a core feature of schizophrenia (SCZ). The "disembodied" self might be underpinned by inefficient body-related multisensory integration processes, normally occurring in the peripersonal space (PPS), a plastic sector of space surrounding the body whose extent is altered in SCZ. Although PPS is a malleable interface marking the perceptual border between self and others, no study has addressed the potential alteration of its plasticity in SCZ. We investigated the plasticity of PPS in SCZ patients after a motor training with a tool in the far space.

STUDY DESIGN

Twenty-seven SCZ patients and 32 healthy controls (HC) underwent an audio-tactile task to estimate PPS boundary before (Session 1) and after (Session 3) the tool-use. Parameters of PPS, including the size and the slope of the psychometric function describing audio-tactile RTs as a function of the audio-tactile distances, were estimated.

STUDY RESULTS

Results confirm a narrow PPS extent in SCZ. Surprisingly, we found PPS expansion in both groups, thus showing for the first time a preserved PPS plasticity in SCZ. Patients experienced a weaker differentiation from others, as indicated by a shallower PPS slope at Session 1 that correlated positively with negative symptoms. However, at Session 3, patients marked their bodily boundary in a steeper way, suggesting a sharper demarcation of PPS boundaries after the action with the tool.

CONCLUSIONS

These findings highlight the importance of investigating the multisensory and motor roots of self-disorders, paving the way for future body-centred rehabilitation interventions that could improve patients' altered body boundary.