Distorted body representations in healthy cognition

Delusions and misperceptions about the body are a conspicuous feature of numerous neurological and psychiatric conditions. In stark contrast to such pathological cases, the immediacy and familiarity of our ordinary experience of our body can make it seem as if our representation of our body is highly accurate, even infallible. Recent research has begun to demonstrate, however, that large and systematic distortions of body representation are a normal part of healthy cognition. Here, I describe this research, focusing on distortions of body representations underlying tactile distance perception and position sense. I also discuss evidence for distortions of higher-order body representations, such as the conscious body image. Finally, I will end with a discussion of the potential relations among different body representations and their distortions.     

Co-ordination of bimanual movements in a centrally deafferented patient executing open loop reach-to-grasp movements

Many everyday tasks require that we use our hands co-operatively. For tasks where both hands are required to perform the same action, a common motor program can be used. But, where each hand must perform a different action, some degree of independent control of each hand is required. In this paper we examine the co-ordination of bimanual movement kinematics in a female patient recovering from brain injury involving anterior regions of the parietal lobe of the right hemisphere, which has resulted in a dense hemianaesthesia of her left arm. A particular focus of this paper is the co-ordination of bimanual movements for reaches executed without visual feedback. Specifically we present new data, which quantify the synchronisation of patient D.B.'s hands by comparing their relative time lag at the start and the end of her bimanual reaches. The results are discussed with particular reference to the role played by limb proprioception in the planning and control of prehension movements.     

Handwriting on a tablet screen: Role of visual and proprioceptive feedback in the control of movement by children and adults

Tablets are increasingly being used in schools for a variety of handwriting tasks. Given that the control of handwriting relies on both visual and proprioceptive feedback, especially in younger writers, this raises the question of whether the texture of the tablet surface affects graphomotor execution. A series of recent studies found that when the smoothness of a tablet screen modifies proprioceptive feedback, the impact on graphomotor execution varies according to the level of the writer’s handwriting skills. However, as the writing on the screen remained visible in these studies, participants may have compensated for the decrease in proprioceptive feedback by relying more heavily on visual information. The aim of the present study was therefore to unravel the respective contributions of different types of sensory feedback during handwriting development and, consequently, the compensatory role of visual information when children and adults have to write on a tablet. To this end, we asked second and fifth graders and adult participants to write letters and pseudowords on a plastic board placed on top of a tablet screen. Participants wrote on either the smooth or the granular side of the plastic board (manipulation of surface friction), and with normal vision or behind a shield that hid the hand and handwriting from direct view (manipulation of vision). Kinematic parameters and legibility were recorded to assess handwriting performances. Results revealed a significant interaction between proprioceptive and visual feedback on letter size, pen speed and legibility, regardless of participants’ age. Furthermore, reducing the visual and proprioceptive feedback had a greater effect on the children’s handwriting performances than on those of adults. Overall, the present study provides new insight into the contribution of the different types of sensory feedback and their interaction with handwriting development. In addition, our results on the impact of tablet surface on graphomotor execution will serve as useful pointers for improving the design of this tool for children, such as increasing the degree of friction of the screen surface.     

Proprioceptive impairments associated with knee osteoarthritis are not generalized to the ankle and elbow joints

The mechanisms for proprioceptive changes associated with knee osteoarthritis (OA) remain elusive. Observations of proprioceptive changes in both affected knees and other joints imply more generalized mechanisms for proprioceptive impairment. However, evidence for a generalized effect remains controversial. This study examined whether joint repositioning proprioceptive deficits are localized to the diseased joint (knee) or generalized across other joints (elbow and ankle) in people with knee OA. Thirty individuals with right knee OA (17 female, 66 ± 7 [mean ± SD] years) of moderate/severe radiographic disease severity and 30 healthy asymptomatic controls of comparable age (17 female, 65 ± 8 years) performed active joint repositioning tests of the knee, ankle and elbow in randomised order in supine. Participants with knee OA had a larger relative error for joint repositioning of the knee than the controls (OA: 2.7 ± 2.1°, control: 1.6 ± 1.7°, p = .03). Relative error did not differ between groups for the ankle (OA: 2.2 ± 2.5°, control: 1.9 ± 1.3°, p = .50) or elbow (OA: 2.5 ± 3.3°, control: 2.9 ± 2.8°, p = .58). These results are consistent with a mechanism for proprioceptive change that is localized to the knee joint. This could be mediated by problems with mechanoreceptors, processing/relay of somatosensory input to higher centers, or joint-specific interference with cognitive processes by pain.     

Action planning and position sense in children with Developmental Coordination Disorder

The present study examined action planning and position sense in children with Developmental Coordination Disorder (DCD). Participants performed two action planning tasks, the sword task and the bar grasping task, and an active elbow matching task to examine position sense. Thirty children were included in the DCD group (aged 6–10 years) and age-matched to 90 controls. The DCD group had a MABC-2 total score ⩽5th percentile, the control group a total score ⩾25th percentile. Results from the sword-task showed that children with DCD planned less for end-state comfort. On the bar grasping task no significant differences in planning for end-state comfort between the DCD and control group were found. There was also no significant difference in the position sense error between the groups. The present study shows that children with DCD plan less for end-state comfort, but that this result is task-dependent and becomes apparent when more precision is needed at the end of the task. In that respect, the sword-task appeared to be a more sensitive task to assess action planning abilities, than the bar grasping task. The action planning deficit in children with DCD cannot be explained by an impaired position sense during active movements.     

Development of interactions between sensorimotor representations in school-aged children

Reliable sensory-motor integration is a pre-requisite for optimal movement control; the functionality of this integration changes during development. Previous research has shown that motor performance of school-age children is characterized by higher variability, particularly under conditions where vision is not available, and movement planning and control is largely based on kinesthetic input. The purpose of the current study was to determine the characteristics of how kinesthetic-motor internal representations interact with visuo-motor representations during development. To this end, we induced a visuo-motor adaptation in 59 children, ranging from 5 to 12 years of age, as well as in a group of adults, and measured initial directional error (IDE) and endpoint error (EPE) during a subsequent condition where visual feedback was not available, and participants had to rely on kinesthetic input. Our results show that older children (age range 9–12 years) de-adapted significantly more than younger children (age range 5–8 years) over the course of 36 trials in the absence of vision, suggesting that the kinesthetic-motor internal representation in the older children was utilized more efficiently to guide hand movements, and was comparable to the performance of the adults.     

Older adults demonstrate greater accuracy in joint position matching using self-guided movements

Greater proprioceptive accuracy has been found with active compared to passive movement. Therapeutic approaches in rehabilitation include varying levels of assistance with arm movements. This assistance may impact proprioceptive acuity. Eighteen older adults participated in a joint repositioning study. The ability to independently reproduce a shoulder flexion angle was investigated when the reference angle was set under the following conditions: (1) the examiner actively assisted participant’s motion to the reference angle chosen by the examiner, (2) the participant moved independently, but the examiner provided tactile cueing to stop at the reference angle chosen by the examiner, and (3) the participant independently moved to a self-selected reference angle. Participants were most accurate in the self-guided condition compared to the active assisted or tactile cueing conditions. Both the self-guided and tactilely cued conditions involved active movement, yet accuracy differed. In contrast, there was no difference in accuracy between the active assisted and tactile cueing conditions despite one involving more active movement. The results demonstrate active movement alone does not determine accuracy. External stimuli, either tactile input and/or a reference angle chosen by the examiner may diminish accuracy. This can be clinically relevant as proprioceptive performance has been linked to improved motor performance.     

The effects of trunk extensor and abdominal muscle fatigue on postural control and trunk proprioception in young,healthy individuals

The purpose of this study was to induce both trunk extensor and abdominal muscle fatigue, on separate occasions, and compare their effects on standing postural control and trunk proprioception, as well as look at the effects of a recovery period on these outcome measures. A total of 20 individuals participated, with 10 (5 males and 5 females) completing either a standing postural control or lumbar axial repositioning protocol. Participants completed their randomly assigned protocol on two occasions, separated by at least 4 days, with either their trunk extensor or abdominal muscles being fatigued on either day. Postural control centre of pressure variables and trunk proprioception errors were compared pre- and post-fatigue. Results showed that both trunk extensor and abdominal muscle fatigue significantly degraded standing postural control immediately post-fatigue, with recovery occurring within 2 min post-fatigue. In general, these degradative effects on postural control appeared to be greater when the trunk extensor muscles were fatigued compared to the abdominal muscles. No statistically significant changes in trunk proprioception were found after either fatigue protocol. The present findings demonstrate our body’s ability to quickly adapt and reweight somatosensory information to maintain postural control and trunk proprioception, as well as illustrate the importance of considering the abdominal muscles, along with the trunk extensor muscles, when considering the impact of fatigue on trunk movement and postural control.