Tool-use Extends Peripersonal Space Boundaries in Schizophrenic Patients

Abstract

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.

The Remapping of Peripersonal Space in a Real but Not in a Virtual Environment

“…Thus, RTs were entered in a repeated-measures ANOVA with sensory modality (multisensory, unisensory) as the within-subjects factor. The ANOVA showed a significant main effect of sensory modality (F (1,20) = 55.77, p < 0.001, η 2 p = 0.74), showing that multisensory RTs (multisensory: M = 521.83, SE = 12.58) were faster than the unisensory tactile ones (unisensory: M = 604.11, SE = 16.64), demonstrating a clear multisensory facilitation effect in line with previous studies e.g., [ 9 , 46 ].…”

“…Lastly, to estimate the individual boundary of PPS, PSE (point of subjective equality) of the psychometric function describing visuo-tactile RTs as a function of visuo-tactile distance was measured via the Spearman–Karber (SK) method [ 47 , 48 ] in line with recent studies on PPS [ 9 , 29 , 46 ]. For more specific details about the implemented procedure, please refer to the Supplementary Materials (Section 2) .…”

“…This region of space is a multisensory space where visual or auditory inputs related to the environment are integrated with tactile and proprioceptive information concerning specific body parts [ 1 , 4 , 5 , 6 ]. This spatial representation remaps plastically after different experiences, e.g., it expands after tool use [ 7 , 8 , 9 , 10 , 11 ], it contracts after immobilization [ 12 ], it blurs after sensory deprivation [ 13 ], or it is modulated by the type of social context [ 14 , 15 ]. Several studies have described the changes in the representation of PPS after interacting with physical tools [ 16 , 17 , 18 ].…”

Social Context and Tool Use Can Modulate Interpersonal Comfort Space

“…Two points of our results are worth pointing out. First, the general increase in the distance due to simple tool use gives further support to the motor plasticity attributed to the representation of the space around the body conceived as reaching space (e.g., [ 63 , 64 , 65 ]).The active use of a long tool extends the representation of the reachable space by ideally expanding the point at which one might act and by confirming a close relationship between the arm action capabilities and reaching space (e.g., [ 11 , 18 , 42 , 44 , 45 , 46 , 47 , 63 , 64 , 65 , 66 ]). Moreover, in line with the existent data, tool use modifies the reaching distance towards a potentially relevant social stimulus (e.g., [ 39 , 40 ]).…”

“…However, further studies are needed to understand to what extent and under what conditions these two spaces may reveal similar behavioural displays. Furthermore, many studies have identified alterations of the representation of the space around the body in neurological [ 70 ], psychopathological [ 64 , 71 , 72 ] or autistic [ 19 ] patients. Therefore, in-depth knowledge of the mechanisms of sharing or segregation between action space and interpersonal social space may potentially suggest new ways to improve or rehabilitate the functions of representing the space around our bodies.…”