Facilitation of imitative movement in patients with chronic hemiplegia triggered by illusory ownership.

The sense of body ownership, the feeling that one's body belongs to oneself, is a crucial subjective conscious experience of one's body. Recent methodological advances regarding crossmodal illusions have provided novel insights into how multisensory interactions shape human perception and cognition, underpinning conscious experience, particularly alteration of body ownership. Moreover, in post-stroke rehabilitation, encouraging the use of the paretic limb in daily life is considered vital, as a settled sense of ownership and attentional engagement toward the paralyzed body part may promote increased frequency of its use and prevent learned nonuse. Therefore, in addition to traditional methods, novel interventions using neurorehabilitation techniques that induce self-body recognition are needed. This study investigated whether the illusory experience of a patient's ownership alterations of their paretic hand facilitates the enhancement in the range of motion of succeeding imitation movements. An experiment combining a modified version of the rubber hand illusion with imitation training was conducted with chronic hemiplegia. A larger imitation movement of the paretic hand was observed in the illusion-induced condition, indicating that the feeling of ownership toward the observed limb promotes the induction of intrinsic potential for motor performance. This training, using subjective experience, may help develop new post-stroke rehabilitation interventions.

Quantitative measurement of finger usage in stroke hemiplegia using ring-shaped wearable devices.

BACKGROUND: In post-stroke rehabilitation, positive use of affected limbs in daily life is important to improve affected upper-limb function. Several studies have quantitatively evaluated the amount of upper-limb activity, but few have measured finger usage. In this study, we used a ring-shaped wearable device to measure upper-limb and finger usage simultaneously in hospitalized patients with hemiplegic stroke and investigated the association between finger usage and general clinical evaluation. METHODS: Twenty patients with hemiplegic stroke in an inpatient hospital participated in this study. All patients wore a ring-shaped wearable device on both hands for 9 h on the day of the intervention, and their finger and upper-limb usage were recorded. For the rehabilitation outcome assessments, the Fugl-Meyer Assessment of the Upper Extremity (FMA-UE), Simple Test for Evaluating Hand Function (STEF), Action Research Arm Test (ARAT), Motor Activity Log-14 (MAL), and Functional Independence Measure Motor (FIM-m) were performed and evaluated on the same day as the intervention. RESULTS: Finger usage of the affected hand was moderately correlated with STEF ([Formula: see text], [Formula: see text]) and STEF ratio ([Formula: see text], [Formula: see text]). The finger-usage ratio was moderately correlated with FMA-UE ([Formula: see text], [Formula: see text]) and ARAT ([Formula: see text], [Formula: see text]), and strongly correlated with STEF ([Formula: see text], [Formula: see text]) and STEF ratio ([Formula: see text], [Formula: see text]). The upper-limb usage of the affected side was moderately correlated with FMA-UE ([Formula: see text], [Formula: see text]), STEF ([Formula: see text], [Formula: see text]) and STEF ratio ([Formula: see text], [Formula: see text]), and strongly correlated with ARAT ([Formula: see text], [Formula: see text]). The upper-limb usage ratio was moderately correlated with ARAT ([Formula: see text], [Formula: see text]) and STEF ([Formula: see text], [Formula: see text]), and strongly correlated with the STEF ratio ([Formula: see text], [Formula: see text]). By contrast, there was no correlation between MAL and any of the measurements. CONCLUSIONS: This measurement technique provided useful information that was not biased by the subjectivity of the patients and therapists.

Decreased Tactile Sensitivity Induced by Disownership: An Observational Study Utilizing the Rubber Hand Illusion.

The sense of body ownership, the feeling that one's own body belongs to oneself, is generated from the integration of visual, tactile, and proprioceptive information. However, long-term non-use of parts of the body due to physical dysfunction caused by trauma or illness may disturb multisensory integration, resulting in a decreased sense of body ownership. The rubber hand illusion (RHI) is an experimental method of manipulating the sense of ownership (SoO). In this illusion, subjects feel as if the rubber hand in front of them were their own hand. The RHI elicits the disownership phenomenon; not only does the rubber hand feels like one's own hand, but one's own hand does not feel like one's own hand. The decrease of ownership of one's own body induced by the bodily illusion is accompanied by neurophysiological changes, such as attenuation of somatosensory evoked potential and decreases in skin temperature. If the loss of the SoO is associated with decreased neurophysiological function, the dysfunction of patients complaining of the loss of ownership can be exacerbated; appropriate rehabilitation prescriptions are urgently required. The present study attempted to induce a sense of disownership of subjects' own hands using the RHI and investigated whether the tactile sensitivity threshold was altered by disownership. Via questionnaire, subjects reported a decrease of ownership after the RHI manipulation; at the same time, tactile sensitivity thresholds were shown to increase in tactile evaluation using the Semmes-Weinstein monofilaments test. The tactile detection rate changes before and after the RHI were negatively correlated with the disownership-score changes. These results show that subjects' sense of disownership, that their own hands did not belong to them, led to decreases in tactile sensitivity. The study findings also suggest that manipulating of illusory ownership can be a tool for estimating the degree of exacerbation of sensory impairment in patients. Consideration of new interventions that optimize the sense of body ownership may contribute to new rehabilitation strategies for post-stroke sensory impairment.

Relationship Between Body-Specific Attention to a Paretic Limb and Real-World Arm Use in Stroke Patients: A Longitudinal Study.

Learned nonuse is a major problem in upper limb (UL) rehabilitation after stroke. Among the various factors that contribute to learned nonuse, recent studies have focused on body representation of the paretic limb in the brain. We previously developed a method to measure body-specific attention, as a marker of body representation of the paretic limb and revealed a decline in body-specific attention to the paretic limb in chronic stroke patients by a cross-sectional study. However, longitudinal changes in body-specific attention and paretic arm use in daily life (real-world arm use) from the onset to the chronic phase, and their relationship, remain unknown. Here, in a longitudinal, prospective, observational study, we sought to elucidate the longitudinal changes in body-specific attention to the paretic limb and real-world arm use, and their relationship, by using accelerometers and psychophysical methods, respectively, in 25 patients with subacute stroke. Measurements were taken at baseline (TBL), 2 weeks (T2w), 1 month (T1M), 2 months (T2M), and 6 months (T6M) after enrollment. UL function was measured using the Fugl-Meyer Assessment (FMA) and Action Research Arm Test (ARAT). Real-world arm use was measured using accelerometers on both wrists. Body-specific attention was measured using a visual detection task. The UL function and real-world arm use improved up to T6M. Longitudinal changes in body-specific attention were most remarkable at T1M. Changes in body-specific attention up to T1M correlated positively with changes in real-world arm use up to T6M, and from T1M to T6M, and the latter more strongly correlated with changes in real-world arm use. Changes in real-world arm use up to T2M correlated positively with changes in FMA up to T2M and T6M. No correlation was found between body-specific attention and FMA scores. Thus, these results suggest that improved body-specific attention to the paretic limb during the early phase contributes to increasing long-term real-world arm use and that increased real-world use is associated with the recovery of UL function. Our results may contribute to the development of rehabilitation strategies to enhance adaptive changes in body representation in the brain and increase real-world arm use after stroke.

Synchronous Neural Oscillation Between the Right Inferior Fronto-Parietal Cortices Contributes to Body Awareness.

The right inferior fronto-parietal network monitors the current status of the musculoskeletal system and builds-up and updates our postural model. The kinesthetic illusion induced by tendon vibration has been utilized in experiments on the modulation of body awareness. The right inferior fronto-parietal cortices activate during the kinesthetic illusion. We aimed to determine the relationship between the right inferior fronto-parietal cortices and body awareness by applying transcranial alternating current stimulation (tACS) to exogenously modulate oscillatory neural activity in the right fronto-parietal cortices during the kinesthetic illusion. Sixteen young adults participated in this study. We counterbalanced the order in which participants received the three types of tACS (55 Hz enveloped by 6 Hz; synchronous, desynchronous, and sham) across the subjects. The illusory movement perception induced by tendon vibration of the left extensor carpi ulnaris muscle was assessed before and during tACS. Application of synchronous tACS over the right inferior fronto-parietal cortices significantly increased kinesthetic illusion compared with sham tACS. The kinesthetic illusion during desynchronous tACS decreased from baseline. There was no change in vibration sensation during any tACS condition. The modulation of oscillatory brain activity between the right fronto-parietal cortices alters the illusory movement perception without altering actual vibration sensation. tACS over the right inferior fronto-parietal cortices is considered to modulate the neural processing involved in updating the postural model when the stimulated muscle spindle sends kinesthetic signals. This is the first study that reveals that rhythmic communication between the right inferior fronto-parietal cortices has a causal role in body awareness.

Maladaptive change of body representation in the brain after damage to central or peripheral nervous system.

Our brain has great flexibility to cope with various changes in the environment. Use-dependent plasticity, a kind of functional plasticity, plays the most important role in this ability to cope. For example, the functional recovery of paretic limb motor movement during post-stroke rehabilitation depends mainly on how much it is used. Patients with hemiparesis, however, tend to gradually disuse the paretic limb because of its motor impairment. Decreased use of the paretic hand then leads to further functional decline brought by use-dependent plasticity. To break this negative loop, body representation, which is the conscious and unconscious information regarding body state stored in the brain, is key for using the paretic limb because it plays an important role in selecting an effector while a motor program is generated. In an attempt to understand body representation in the brain, we reviewed animal and human literature mainly on the alterations of the sensory maps in the primary somatosensory cortex corresponding to the changes in limb usage caused by peripheral or central nervous system damage.

Egocentric mental transformation of self: effects of spatial relationship in mirror-image and anatomic imitations.

Assessing the mental state of others by considering their perspective plays an important part in social communication. Imitation based on visual information represents a typical case of the translation of sensory input into action. Although humans are often successful in imitating complex actions, the mechanisms that underlie successful imitation are poorly understood. In earlier findings, it has been suggested that understanding others' minds through imitation is realized in the course of the comparison between the representations of the self and others, involving a transformation of the egocentric perspective to the allocentric one. There are two possible strategies of transformation between the representation of the self and others. One possible scenario is that the imitator perceives and imitates others as if looking in a mirror (mirror-image imitation, where, for example, the demonstrator's right hand corresponds to the imitator's left hand). Alternatively, the imitator might estimate the demonstrator's action using the anatomically congruent limb (anatomic imitation, where, for example, the demonstrator's right hand corresponds to the imitator's right hand). Here, we conducted a series of experiments in which the subjects imitated simple hand actions such as pushing a button presented from several different spatial orientations rotated at various angles. We observed that the imitators changed their strategy of imitation (mirror-image or anatomic imitation) depending on the nature of spatial configurations. Behavioral data from this study support the hypothesis that mirror-image and anatomic imitations provide complementary systems for understanding the actions and intentions of others.