Abstract
Decades of research have demonstrated a role for the hippocampus in spatial navigation and episodic and spatial memory. However, empirical evidence linking hippocampal activity to the perceptual experience of being physically located at a particular place in the environment is lacking. In this study, we used a multisensory out-of-body illusion to perceptually ‘teleport’ six healthy participants between two different locations in the scanner room during high-resolution functional magnetic resonance imaging (fMRI). The participants were fitted with MRI-compatible head-mounted displays that changed their first-person visual perspective to that of a pair of cameras placed in one of two corners of the scanner room. To elicit the illusion of being physically located in this position, we delivered synchronous visuo-tactile stimulation in the form of an object moving toward the cameras coupled with touches applied to the participant’s chest. Asynchronous visuo-tactile stimulation did not induce the illusion and served as a control condition. We found that illusory self-location could be successfully decoded from patterns of activity in the hippocampus in all of the participants in the synchronous (P < 0.05) but not in the asynchronous condition (P > 0.05). At the group-level, the decoding accuracy was significantly higher in the synchronous than in the asynchronous condition (P = 0.012). These findings associate hippocampal activity with the perceived location of the bodily self in space, which suggests that the human hippocampus is involved not only in spatial navigation and memory but also in the construction of our sense of bodily self-location.
Highlights
An extensive history of neurophysiological studies in rats has demonstrated that the hippocampus is crucial for the construction of internal representations of the spatial environment (O’Keefe and Nadel, 1978; Andersen, 2007; Moser et al, 2008)
We exclusively analyzed the period when the dark curtain was presented and performed a control analysis on the asynchronous condition, which was perfectly matched in terms of visual input, to ensure that the internal representation of self-location constituted the key difference between the four experimental conditions
The results showed that perceived self-location could be decoded with remarkable consistency: hippocampal activity patterns significantly distinguished the locations in all six participants in the synchronous condition (P < 0.05, corrected, permutation test with 10,000 iterations; Figures 2A,C)
Summary
An extensive history of neurophysiological studies in rats has demonstrated that the hippocampus is crucial for the construction of internal representations of the spatial environment (O’Keefe and Nadel, 1978; Andersen, 2007; Moser et al, 2008). Decoding self-location from the human hippocampus the perceptual experience of being physically located at a particular place in the environment. To address this question, we adapted a perceptual out-ofbody illusion (Ehrsson, 2007; Guterstam and Ehrsson, 2012) to the environment of an MRI scanner. To induce the illusion of being physically located at one of these two locations, the experimenter simultaneously touched the participant’s real chest, which was out of view, and the chest of the ‘illusory body,’ which was located in the corner of the room, just below the field of view (FOV) of the HMDs (Figure 1B). In half of the trials, the touching of the real chest and the ‘illusory chest’ occurred asynchronously, which is a mode of visuo-tactile stimulation that significantly reduces the illusion and allows for the comparison of otherwise equivalent conditions (Ehrsson, 2007; Guterstam and Ehrsson, 2012)
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