Multisensory and Sensorimotor Integration in the Embodied Self: Relationship between Self-Body Recognition and the Mirror Neuron System

Abstract

The embodied self is rooted in the self-body in the "here and now". The senses of self-ownership and self-agency have been proposed as the basis of the sense of embodied self, and many experimental studies have been conducted on this subject. This review summarizes the experimental research on the embodied self that has been conducted over the past 20 years, mainly from the perspective of multisensory integration and sensorimotor integration regarding the self-body. Furthermore, the phenomenon of back projection, in which changes in an external object (e.g., a rubber hand) with which one has a sense of ownership have an inverse influence on the sensation and movement of one's own body, is discussed. This postulates that the self-body illusion is not merely an illusion caused by multisensory and/or sensorimotor integration, but is the incorporation of an external object into the self-body representation in the brain. As an extension of this fact, we will also review research on the mirror neuron system, which is considered to be the neural basis of recognition of others, and discuss how the neural basis of self-body recognition and the mirror neuron system can be regarded as essentially the same.

Keywords: back projection; full body illusion; functional neuroimaging; mirror neuron system; robot hand illusion; rubber hand illusion; sense of agency; sense of ownership.

Figure 1

Forward model. The motor commands are sent to the sensori-motor system and the results are returned as actual sensory feedback. Meanwhile, copy information (efference copy) of the motor command is sent to the internal predictor, which generates predictive sensory feedback. By comparing these signals, inconsistency between the intended and actual outcomes is detected.

Figure 2

Active and passive vision-movement asynchrony judgement task [14]. (A) experimental settings. (B) A representative result. The time window for detecting visual feedback delay is nearly equivalent for active and passive movements, while the steepness of the slope is steeper for active movement than for passive movement.

Figure 3

Event-related potential components for self-generated delayed sounds, related to sensory attenuation and the sense of agency [24]. The N1 component is significantly suppressed (sensory attenuation) in the control (no delay) and 100–300 ms delay conditions, but not in the 400 ms delay condition. The N300 component becomes greater as the delay increased, which reflected the attenuation of the sense of agency.

Figure 4

(A) The sense of ownership and (B) agency in robot hand illusion [41]. Both senses showed significant reductions in the 290-ms and 590-ms conditions, with the major difference being that the sense of agency was significantly felt in the 290–490-ms conditions, while the sense of ownership was not. (C) The right angular gyrus was significantly activated when the robot hand illusion was felt in the 100 ms condition compared to the 400 and 700 ms conditions [42,43].

Figure 5

Full-body illusion from the first- and third-person perspective. (A) The sense of ownership was felt only in the synchronous first-person perspective (1PP) condition, while the sense of agency was felt in the synchronous 1PP and third-person perspective (3PP) conditions. (B) Examples of a VR scene presented to the participants [51].

Figure 6

The mirror neuron system. It is activated not only when the individual performs a certain action, but also when he or she observes others performing the same action.

Figure 7

Functional connectivity between player and observer in cheering [74]. The connectivity between the player’s motor cortex and the observer’s mirror neuron system was significantly enhanced when the player won compared to when the player lost.

Figure 8

A model for self-body recognition and mirror neuron system. In self-body recognition (left), the vision (extrinsic body information) is compared with the intrinsic (proprioceptive, somatosensory, or motor) body information. In the mirror neuron system (right), extrinsic body information drives intrinsic, especially motor, body representation.

Figure 9

Self-body recognition and the mirror neuron system. Extrinsic (vision, sound) and intrinsic (proprioceptive, somatosensory, and motor) body information are integrated in the parietal lobe. If those are consistent, the self-body image emerges in the superior parietal and intraparietal regions, and possibly extends to the premotor cortex, consisting of mirror neuron system, otherwise representations of others emerge in the TPJ and/or STS regions.