Combined EEG and immersive virtual reality unveil dopaminergic modulation of error monitoring in Parkinson's Disease.

Detecting errors in your own and others' actions is associated with discrepancies between intended and expected outcomes. The processing of salient events is associated with dopamine release, the balance of which is altered in Parkinson's disease (PD). Errors in observed actions trigger various electrocortical indices (e.g. mid-frontal theta, error-related delta, and error positivity [oPe]). However, the impact of dopamine depletion to observed errors in the same individual remains unclear. Healthy controls (HCs) and PD patients observed ecological reach-to-grasp-a-glass actions performed by a virtual arm from a first-person perspective. PD patients were tested under their dopaminergic medication (on-condition) and after dopaminergic withdrawal (off-condition). Analyses of oPe, delta, and theta-power increases indicate that while the formers were elicited after incorrect vs. correct actions in all groups, the latter were observed in on-condition but altered in off-condition PD. Therefore, different EEG error signatures may index the activity of distinct mechanisms, and error-related theta power is selectively modulated by dopamine depletion. Our findings may facilitate discovering dopamine-related biomarkers for error-monitoring dysfunctions that may have crucial theoretical and clinical implications.

Immersive virtual reality reveals that visuo-proprioceptive discrepancy enlarges the hand-centred peripersonal space.

Vision and proprioception, informing the system about the body position in space, seem crucial in defining the boundary of the peripersonal space (PPS). What happens to the PPS representation when a conflict between vision and proprioception arises? We capitalize on the Immersive Virtual Reality to dissociate vision and proprioception by presenting the participants' 3D hand image in congruent/incongruent positions with respect to the participants' real hand. To measure the hand-centred PPS, we exploit multisensory integration occurring when visual stimuli are delivered simultaneously with tactile stimuli applied to a body district; i.e., visual enhancement of touch (VET). Participants are instructed to respond to tactile stimuli while ignoring visual stimuli (red LED), which can appear either near to or far from the hand receiving tactile (electrical) stimuli. The results show that, when vision and proprioception are congruent (i.e., real and virtual hand coincide), a space-dependent modulation of the VET effect occurs (with faster responses when visual stimuli are near to than far from the stimulated hand). Contrarily, when vision and proprioception are incongruent (i.e., a discrepancy between real and virtual hand is present), a comparable VET effect is observed when visual stimuli occur near to the real hand and when they occur far from it, but close to the virtual hand. These findings, also confirmed by the independent estimate of a Bayesian Causal Inference model, suggest that, when the visuo-proprioceptive discrepancy makes the coding of the hand position less precise, the hand-centred PPS is enlarged, likely to optimize reactions to external events.

Influence of cognitive stance and physical perspective on subjective and autonomic reactivity to observed pain and pleasure: An immersive virtual reality study.

Observing others' pain may induce a reaction called personal distress that may be influenced by top-down (imagine self or other in pain, i.e., self- vs other-oriented stance) and bottom-up (physical perspective of those who suffer, i.e., first vs third person perspective- 1PP vs 3PP) processes. The different contributions of these processes have not been teased apart. By capitalizing on the power of Immersive Virtual Reality, we explored how behavioural (subjective ratings) and physiological reactivity (skin conductance reactivity, SCR) to pain and pleasure delivered to an avatar was influenced by Cognitive stance and Physical perspective. Taking an Other-Oriented stance leads to attributing higher congruent valence (i.e. pain rated as unpleasant and pleasure as pleasant) and intensity to the stimuli and induces reduced SCR. Ownership over the virtual limb was maximal in 1PP where physiological reactivity to the stimuli was comparable. Our results highlight different components underpinning reactivity to pain and pleasure.

Wronger than wrong: Graded mapping of the errors of an avatar in the performance monitoring system of the onlooker.

EEG studies show that observing errors in one's own or others' actions triggers specific electro-cortical signatures in the onlooker's brain, but whether the brain error-monitoring system operates according to graded or discrete rules is still largely unknown. To explore this issue, we combined immersive virtual reality with EEG recording in participants who observed an avatar reaching-to-grasp a glass from a first-person perspective. The avatar could perform correct or erroneous actions. Erroneous grasps were defined as small or large depending on the magnitude of the trajectory deviation from the to-be-grasped glass. Results show that electro-cortical indices of error detection (indexed by ERN and mid-frontal theta oscillations), but not those of error awareness (indexed by error-Positivity), were gradually modulated by the magnitude of the observed errors. Moreover, the phase connectivity analysis revealed that enhancement of mid-frontal theta phase synchronization paralleled the magnitude of the observed error. Thus, theta oscillations represent an electro-cortical index of the degree of control exerted by mid-frontal regions whose activation depends on how much an observed action outcome results maladaptive for the onlooker. Our study provides novel neurophysiological evidence that the error monitoring system maps observed errors of different magnitude according to fine-grain, graded rather than all-or-none rules.

Seeing pain and pleasure on self and others: behavioral and psychophysiological reactivity in immersive virtual reality.

Studies have explored behavioral and neural responses to the observation of pain in others. However, much less is known about how taking a physical perspective influences reactivity to the observation of others' pain and pleasure. To explore this issue we devised a novel paradigm in which 24 healthy participants immersed in a virtual reality scenario observed a virtual: needle penetrating (pain), caress (pleasure), or ball touching (neutral) the hand of an avatar seen from a first (1PP)- or a third (3PP)-person perspective. Subjective ratings and physiological responses [skin conductance responses (SCR) and heart rate (HR)] were collected in each trial. All participants reported strong feelings of ownership of the virtual hand only in 1PP. Subjective measures also showed that pain and pleasure were experienced as more salient than neutral. SCR analysis demonstrated higher reactivity in 1PP than in 3PP. Importantly, vicarious pain induced stronger responses with respect to the other conditions in both perspectives. HR analysis revealed equally lower activity during pain and pleasure with respect to neutral. SCR may reflect egocentric perspective, and HR may merely index general arousal. The results suggest that behavioral and physiological indexes of reactivity to seeing others' pain and pleasure were qualitatively similar in 1PP and 3PP. Our paradigm indicates that virtual reality can be used to study vicarious sensation of pain and pleasure without actually delivering any stimulus to participants' real body and to explore behavioral and physiological reactivity when they observe pain and pleasure from ego- and allocentric perspectives.

Re-establishing the disrupted sensorimotor loop in deafferented and deefferented people: The case of spinal cord injuries.

Acting efficiently in the world depends on the activity of motor and somatosensory systems, the integration of which is necessary for the proper functioning of the sensorimotor loop (SL). Profound alterations of SL functioning follow spinal cord injury (SCI), a condition that brings about a disconnection of the body from the brain. Such disconnection creates a substantial deprivation of somatosensorial inputs and motor outputs. Consequent somatic deficits and motor paralysis affect the body below the lesion level. A complete restoration of normal functions of the SL cannot be expected until basic neuroscience has found a way to re-establish the interrupted neural connectivity. Meanwhile, studies should focus on the development of technical solutions for dealing with the disruption of the sensorimotor loop. This review discusses the structural and functional adaptive reorganization of the brain after SCI, and the maladaptive mechanisms that impact on the processing of body related information, which alter motor imagery strategies and EEG signals. Studies that show how residual functions (e.g. face tactile sensitivity) may help people to restore a normal body image are also reviewed. Finally, data on how brain and residual body signals may be used to improve brain computer interface systems is discussed in relation to the issue of how such systems may help SCI people to re-enter the world and interact with objects and other individuals.

Mere observation of body discontinuity affects perceived ownership and vicarious agency over a virtual hand.

The mental representation of one's body typically implies the continuity of its parts. Here, we used immersive virtual reality to explore whether mere observation of visual discontinuity between the hand and limb of an avatar could influence a person's sense of ownership of the virtual body (feeling of ownership, FO) and being the agent of its actions (vicarious agency, VA). In experiment 1, we tested whether placing different amounts of visual discontinuity between a virtual hand and limb differently modulate the perceived FO and VA. Participants passively observed from a first-person perspective four different versions of a virtual limb: (1) a full limb; a hand detached from the proximal part of the limb because of deletion of (2) the wrist; (3) the wrist and forearm; (4) and the wrist, forearm and elbow. After observing the static or moving virtual limb, participants reported their feeling of ownership (FO) and vicarious agency (VA) over the hand. We found that even a small visual discontinuity between the virtual hand and arm significantly decreased participants' FO over the hand during observation of the static limb. Moreover, in the same condition, we found that passive observation of the avatar's actions induced a decrease in both FO and VA. We replicated the same results in a second study (experiment 2) where we investigated the modulation of FO and VA by comparing the visual body discontinuity with a condition in which the virtual limb was partially occluded. Our data show that mere observation of limb discontinuity can change a person's ownership and agency over a virtual body observed from a first-person perspective, even in the absence of any multisensory stimulation of the real body. These results shed new light on the role of body visual continuity in modulating self-awareness and agency in immersive virtual reality.