Abstract

Rubber hand illusion (RHI), a kind of body ownership illusion, is sometimes atypical in individuals with autism spectrum disorder; however, the brain regions associated with the illusion are still unclear. We previously reported that mice responded as if their own tails were being touched when rubber tails were grasped following synchronous stroking to rubber tails and their tails (a “rubber tail illusion”, RTI), which is a task based on the human RHI; furthermore, we reported that the RTI response was diminished in Ca2+-dependent activator protein for secretion 2-knockout (Caps2-KO) mice that exhibit autistic-like phenotypes. Importance of the posterior parietal cortex in the formation of illusory perception has previously been reported in human imaging studies. However, the local neural circuits and cell properties associated with this process are not clear. Therefore, we aimed to elucidate the neural basis of the RTI response and its impairment by investigating the c-Fos expression in both wild-type (WT) and Caps2-KO mice during the task since the c-Fos expression occurred soon after the neural activation. Immediately following the delivery of the synchronous stroking to both rubber tails and actual tails, the mice were perfused. Subsequently, whole brains were cryo-sectioned, and each section was immunostained with anti-c-Fos antibody; finally, c-Fos positive cell densities among the groups were compared. The c-Fos expression in the posterior parietal cortex was significantly lower in the Caps2-KO mice than in the WT mice. Additionally, we compared the c-Fos expression in the WT mice between synchronous and asynchronous conditions and found that the c-Fos-positive cell densities were significantly higher in the claustrum and primary somatosensory cortex of the WT mice exposed to the synchronous condition than those exposed to the asynchronous condition. Hence, the results suggest that decreased c-Fos expression in the posterior parietal cortex may be related to impaired multisensory integrations in Caps2-KO mice.

Highlights

  • In the rubber hand illusion (RHI) task, a human participant feels as if a rubber hand becomes one’s own hand when the rubber hand and the participant’s hand are stroked synchronously with two brushes (Botvinick and Cohen, 1998; Armel and Ramachandran, 2003; Tsakiris and Haggard, 2005)

  • We further examined the regions where the WT mice exposed to the synchronous condition (n = 6) showed a greater c-Fos cell density than did those exposed to the asynchronous condition (n = 6) in the same way

  • We found that the c-Fos-positive cell densities in the ipsilateral posterior parietal cortex (PPC) and adjacent regions under the synchronous conditions were significantly lower in the Caps2-KO mice than in the WT mice, and densities of c-Fos-positive cells in the regions were generally higher in the WT mice exposed to the synchronous condition than those exposed to the asynchronous condition, the difference did not reach a significant level

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Summary

Introduction

In the rubber hand illusion (RHI) task, a human participant feels as if a rubber hand becomes one’s own hand when the rubber hand and the participant’s hand are stroked synchronously with two brushes (Botvinick and Cohen, 1998; Armel and Ramachandran, 2003; Tsakiris and Haggard, 2005). Visual (i.e., stroking of the rubber hand) and tactile stimuli (i.e., stroking brush of the unseen participant’s own hand) are simultaneously delivered, and perception of tactile stimuli by the brush gradually moves to the rubber hand by the integration of visual and tactile stimuli; illusory body ownership of the rubber hand subsequently occurs. This kind of illusory body ownership is sometimes atypical in individuals with autism spectrum disorder (ASD). They discussed that the delayed occurrence of the RHI may have resulted from atypical multisensory temporal integration

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