ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
To execute the intended movement, the brain directs attention, called body-specific attention, to the body to obtain information useful for movement. Body-specific attention to the hands has been examined but not to the feet. We aimed to confirm the existence of body-specific attention to the hands and feet, and examine its relation to motor and sensory functions from a behavioral perspective. The study included two groups of 27 right-handed and right-footed healthy adults, respectively. Visual detection tasks were used to measure body-specific attention. We measured reaction times to visual stimuli on or off the self-body and calculated the index of body-specific attention score to subtract the reaction time on self-body from that off one. Participants were classified into low and high attention groups based on each left and right body-specific attention index. For motor functions, Experiment 1 comprised handgrip strength and ball-rotation tasks for the hands, and Experiment 2 comprised toe grip strength involved in postural control for the feet. For sensory functions, the tactile thresholds of the hands and feet were measured. The results showed that, in both hands, the reaction time to visual stimuli on the hand was significantly lesser than that offhand. In the foot, this facilitation effect was observed in the right foot but not the left, which showed the correlation between body-specific attention and the normalized toe gripping force, suggesting that body-specific attention affected postural control. In the hand, the number of rotations of the ball was higher in the high than in the low attention group, regardless of the elaboration exercise difficulty or the left or right hand. However, this relation was not observed in the handgripping task. Thus, body-specific attention to the hand is an important component of elaborate movements. The tactile threshold was higher in the high than in the low attention group, regardless of the side in hand and foot. The results suggested that more body-specific attention is directed to the limbs with lower tactile abilities, supporting the sensory information reaching the brain. Therefore, we suggested that body-specific attention regulates the sensory information to help motor control.
