The rubber hand illusion in hypnosis provides new insights into the sense of body ownership

Body ownership can be experimentally investigated with the rubber hand illusion (RHI), in which watching a rubber hand stroked synchronously with one's own hidden hand induces a feeling of ownership over the rubber hand. The aim of this study was to investigate response to the RHI in high (N\u2009=\u200921) and low (N\u2009=\u200919) hypnotizable individuals in normal waking state and in hypnosis. Response to the RHI was measured via a question on the illusory feeling of ownership and with proprioceptive drift. The Highs expressed an overall feeling of more ownership over the rubber hand in both the normal waking state and hypnosis, although both groups gave higher ownership scores after synchronous than after asynchronous stroking and the difference between conditions was similar across groups. Conversely, the proprioceptive drift appeared to be differentially modulated by hypnosis and hypnotic suggestibility: it was increased in the Highs and decreased in the Lows after hypnosis induction. These findings hint at an interplay between hypnotic suggestibility and hypnosis in modulating response to the RHI. The selective breakdown of proprioceptive drift among the Lows suggests resistance to recalibrate one's own limb in hypnosis

Proprioceptive drift is affected by the intermanual distance rather than the distance from the body's midline in the rubber hand illusion

In the rubber hand illusion (RHI), simultaneous brush stroking of a subject's hidden hand and a visible rubber hand induces a transient illusion of the latter to "feel like it's my hand" and a proprioceptive drift of the hidden own hand toward the rubber hand. Recent accounts of the RHI have suggested that the illusion would only occur if weighting of conflicting sensory information and their subsequent integration results in a statistically plausible compromise. In three different experiments, we investigated the role of distance between the two hands as well as their proximity to the body's midline in influencing the occurrence of the illusion. Overall, the results suggest that the illusion is abolished when placing the two hands apart, therefore increasing the mismatch between the visual and proprioceptive modality, whereas the proximity of the two hands to the body's midline plays only a minor role on the subjective report of the illusion. This might be driven by the response properties of visuotactile bimodal cells encoding the peripersonal space around the hand

Trait-related neural basis of attentional bias to emotions: a tDCS study

Negative emotional stimuli can strongly bias attention, particularly in individuals with high levels of dispositional negative affect (NA). The current study investigated whether the prefrontal cortex (PFC), a brain region involved in the top-down regulation of emotional processing, plays a different role in controlling attention to emotions, depending on the individual NA. Sham and anodal transcranial direct current stimulation (tDCS) was delivered over the right or left PFC while assessing attentional bias (AB) to emotions (happy, angry, sad faces) in individuals with higher and lower trait NA. When tDCS was inactive (sham), individuals with higher trait NA showed AB toward angry and away from sad faces, while individuals with lower trait NA presented with no AB. Right anodal-tDCS abolished the AB toward angry faces and induced an AB toward sad faces in individuals with higher trait NA, while no effect was found in individuals with lower trait NA. Left anodal-tDCS abolished any AB in individuals with higher trait NA and induced an AB away from happy faces in individuals with lower trait NA. These findings confirm a critical role of trait NA in AB to emotions and demonstrate a different involvement of PFC in emotional processing based on dispositional affect

Actual and Illusory Perception in Parkinson's Disease and Dystonia: A Narrative Review

Sensory information is continuously processed so as to allow behavior to be adjusted according to environmental changes. Before sensory information reaches the cortex, a number of subcortical neural structures select the relevant information to send to be consciously processed. In recent decades, several studies have shown that the pathophysiological mechanisms underlying movement disorders such as Parkinson's disease (PD) and dystonia involve sensory processing abnormalities related to proprioceptive and tactile information. These abnormalities emerge from psychophysical testing, mainly temporal discrimination, as well as from experimental paradigms based on bodily illusions. Although the link between proprioception and movement may be unequivocal, how temporal tactile information abnormalities and bodily illusions relate to motor disturbances in PD and dystonia is still a matter of debate. This review considers the role of altered sensory processing in the pathophysiology of movement disorders, focusing on how sensory alteration patterns differ between PD and dystonia. We also discuss the evidence available and the potential for developing new therapeutic strategies based on the manipulation of multi-sensory information and bodily illusions in patients with these movement disorders

Hypnosis-induced modulation of corticospinal excitability during motor imagery

Hypnosis can be considered an altered state of consciousness in which individuals produce movements under suggestion without apparent voluntary control. Despite its application in contexts implying motor control, evidence for the neurophysiological mechanisms underlying hypnosis is scarce. Inter-individual differences in hypnotic susceptibility suggest that sensorimotor strategies may manifest in a hypnotic state. We tested by means of transcranial magnetic stimulation applied over the primary motor cortex whether motor system activation during a motor imagery task differs in the awake and in the hypnotic state. To capture individual differences, 30 healthy volunteers were classified as high or low hypnotizable (Highs and Lows) according to ad-hoc validated scales measuring hypnotic susceptibility and personality questionnaires. Corticospinal activation during motor imagery in the hypnotic state was greater in the Highs than the Lows. Intrinsic motivation in task performance and level of persuasion modulated corticospinal activation in the Highs. Corticospinal system activation under hypnosis may have practical implications that merit research in areas where hypnosis can be applied to improve motor performance, such as loss of motor abilities and sports

Functional neurological disorders as seen by a cohort of general practitioners in Northern Italy: evidence from an online survey

General practitioners (GPs) provide primary care and advise their patients on which diagnostic and therapeutic pathways they judge most appropriate. For patients with functional neurological disorders (FND), receiving a proper explanation of diagnosis by their GP from the very beginning may drastically improve prognosis. Novel approaches to the diagnosis and treatment of FND have important implications for effective management. The aim of this study was to investigate Italian GP opinion and knowledge about FND in light of new approaches to the illness. To do this, we evaluated the responses to a 13-item web-based survey completed by 133 GPs practicing in northern Italy. Psychological terms to describe FND were more frequently used than functional neurological disorder and mental illness was considered an important predictor of diagnosis. Referral to a neurologist rather than to a psychiatrist was largely preferred, while physiotherapy consultation was seldom recognized as a valuable approach to treating FND. Overall, the survey findings suggest that knowledge about novel approaches to FND is somewhat lacking. Currently, GPs appear to be transitioning from a classical psychological view of the disorder toward a more modern conceptualization, in which neurobiological, psychological, and social factors all play an important role. Professional education during this transition would be an advantageous way to optimize physician management of FND and to enhance diagnosis, explanation, and management across primary and secondary care pathways

Age-related changes in the sense of body ownership: New insights from the rubber hand illusion

How do age-related changes affect the sense of body ownership? This study tackles this issue by means of the rubber hand illusion (RHI), a widely used experimental tool for investigating the sense of body ownership. There is ample literature on the RHI in young populations, but research on age-related changes in the RHI is still scarce. Here we extend the use of the RHI to examine the changes in the sense of body ownership related to healthy aging. Subjective reports (i.e., questionnaire) and proprioceptive drift were compared among young (n = 22, age range 20-22 years), middle-aged (n = 22, age range 44-55 years), and older adults (n = 22, age range 60-72 years). A stronger subjective experience of illusion was observed in the young and older adults as compared to the middle-aged. No differences in proprioceptive drift were found between the three groups. These findings are discussed in relation to: 1) different stages of development of perceptual and cognitive components of the sense of body ownership, and 2) compensatory mechanisms

Pain, smell, and taste in adults: a narrative review of multisensory perception and interaction

Every day our sensory systems perceive and integrate a variety of stimuli containing information vital for our survival. Pain acts as a protective warning system, eliciting a response to remove harmful stimuli; it may also be a symptom of an illness or present as a disease itself. There is a growing need for additional pain-relieving therapies involving the multisensory integration of smell and taste in pain modulation, an approach that may provide new strategies for the treatment and management of pain. While pain, smell, and taste share common features and are strongly linked to emotion and cognition, their interaction has been poorly explored. In this review, we provide an overview of the literature on pain modulation by olfactory and gustatory substances. It includes adult human studies investigating measures of pain threshold, tolerance, intensity, and/or unpleasantness. Due to the limited number of studies currently available, we have structured this review as a narrative in which we comment on experimentally induced and clinical pain separately on pain-smell and pain-taste interaction. Inconsistent study findings notwithstanding, pain, smell, and taste seem to interact at both the behavioral and the neural levels. Pain intensity and unpleasantness seem to be affected more by olfactory substances, whereas pain threshold and tolerance are influenced by gustatory substances. Few pilot studies to date have investigated these effects in clinical populations. While the current results are promising for the future, more evidence is needed to elucidate the link between the chemical senses and pain. Doing so has the potential to improve and develop novel options for pain treatment

The influence of hands posture on mental rotation of hands and feet

Behavioural and functional neuroanatomy studies demonstrate that mental rotation of body parts is carried out through a sort of inner motor simulation. Here we examined whether changes of hands posture influence the mental rotation of hands and feet. Twenty healthy subjects were asked to verbally judge the laterality of hands and feet pictures in two different postural conditions. In one condition, subjects kept hands on their knees in anatomical position; in the other, their hands were kept in an unusual posture with intertwined fingers, behind the back. Results show that mental rotation of hands but not of feet was influenced by changes in hands posture. Indeed, while mental rotation of hands was faster in the front than in the back hands position, no similar effect was found when mentally rotating feet. Thus, sensory-motor and postural information coming from the body may influence mental rotation of body parts according to specific, somatotopic rules

Performance validity tests in nonlitigant patients with functional motor disorder

Background: Performance Validity Tests (PVTs) are used in neuropsychological assessments to detect patterns of performance suggesting that the broader evaluation may be an invalid reflection of an individual's abilities. Data on Functional motor disorder (FMD) are currently poor and conflicting. Objectives: We aimed to examine the rate of failure at three different PVTs of non-litigant, non-compensation seeking FMD patients, and we compared their performance to that of healthy controls and controls asked to simulate malingering (healthy simulators). Methods: We enrolled 29 non-litigant, non-compensation seeking patients with a clinical diagnosis of FMD, 29 healthy controls and 29 healthy simulators. Three PVTs, the Coin in the Hand Test (CIH), the Rey 15-item Test (REY) and the Finger Tapping Test (FTT), were employed. Results: FMD Patients showed low rates of failure at the CIH and REY tests (7% and 10%, respectively) and slightly higher at the FTT (15%, n=26) test, which implies a motor task. Their performance was statistically comparable to that of healthy controls but statistically different from that of healthy simulators (p<0.001). 93% of FMD patients, 7% of healthy simulators, and 100% of healthy controls passed at least two of the three tests. Conclusions: PVT performance of non-litigant, non-compensation seeking patients with FMD ranged from 7 to 15%. Patient's performance was comparable to controls and significantly differed from that of simulators. This simple battery of three PVTs could be of practical utility and routinely used in clinical practice