Brain Regions Associated to a Kinesthetic Illusion Evoked by Watching a Video of One's Own Moving Hand

Abstract

It is well known that kinesthetic illusions can be induced by stimulation of several sensory systems (proprioception, touch, vision…). In this study we investigated the cerebral network underlying a kinesthetic illusion induced by visual stimulation by using functional magnetic resonance imaging (fMRI) in humans. Participants were instructed to keep their hand still while watching the video of their own moving hand (Self Hand) or that of someone else's moving hand (Other Hand). In the Self Hand condition they experienced an illusory sensation that their hand was moving whereas the Other Hand condition did not induce any kinesthetic illusion. The contrast between the Self Hand and Other Hand conditions showed significant activation in the left dorsal and ventral premotor cortices, in the left Superior and Inferior Parietal lobules, at the right Occipito-Temporal junction as well as in bilateral Insula and Putamen. Most strikingly, there was no activation in the primary motor and somatosensory cortices, whilst previous studies have reported significant activation in these regions for vibration-induced kinesthetic illusions. To our knowledge, this is the first study that indicates that humans can experience kinesthetic perception without activation in the primary motor and somatosensory areas. We conclude that under some conditions watching a video of one's own moving hand could lead to activation of a network that is usually involved in processing copies of efference, thus leading to the illusory perception that the real hand is indeed moving.

Fig 1. Experimental set-up.

The subject's right arm was held by a soft immobilization and he/she could see their right hand through a webcam the output of which was projected onto a screen behind them. A mirror placed before their eyes allowed vision of the screen. They held a custom made push-button with their left hands.

Fig 2. Responses to the questionnaire that participants filled after the last training session (green) and after the fMRI session (blue) to assess ownership feeling over the video projected hand (question 1), the consistency of ownership feeling (question 2), and the vividness of the kinesthetic sensation (question 3).

Histograms are mean responses (+ standard deviation) reported by all participants on 100 mm analogue scales. It is important to note that the Other Hand video was specifically selected so it did not induce any feeling of ownership nor any sensation of movement (cf methods section).

Fig 3. Self Hand > Other Hand.

Voxel level threshold for both contrasts was set at 0.001 uncorrected and voxel level threshold was set at 0.05 FWE corrected. For visualization purpose, statistical maps are displayed on a single subject brain normalized onto the MNI template. Anatomical locations estimated using the Anatomy toolbox (Eickhoff et al. 2006; Eickhoff et al. 2007; Eickhoff et al. 2005) and the Anatomical Automatic Labeling (Tzourio-Mazoyer et al. 2002) are given in Table 3.

Fig 4. Statistical parametric maps for Self Hand > Other Hand and for Real movement > Baseline.

Light blue = Self Hand > Other Hand; yellow = Real movement > Baseline; green = areas common to both contrasts. Voxel level threshold for both contrasts was set at 0.001 uncorrected and cluster level threshold was set at 0.05 FWE corrected. For visualization purpose, statistical maps are displayed on a single subject brain normalized onto the MNI template. Anatomical locations estimated using the Anatomy toolbox (Eickhoff et al. 2006; Eickhoff et al. 2007; Eickhoff et al. 2005) and the Anatomical Automatic Labeling (Tzourio-Mazoyer et al. 2002) are given in Tables 3 and 4.

Fig 5. Percent Signal Change during the Self Hand and the Other Hand conditions for 3 motor Regions of Interest (ROIs).

ROIs were defined for each subject from their individual Real movement > Baseline contrast. For visualization purpose the statistical parametric map for the group analysis of the Real movement > Baseline contrast is projected onto a single subject brain normalized onto the MNI template.