Age-related asymmetry in anticipatory postural movements during unilateral arm movement and imagery.

Reaching movements of the arms are accompanied by anticipatory (APM) and compensatory postural motion (CPM) that counteract the resulting perturbations to body stability. Recent research has shown that these postural actions are also observable in the context of imagined arm movements. As motor imagery (MI) shares many neurophysiological and behavioral characteristics with physical movements, and MI training can affect subsequent performance, MI tasks provide a good setting for studying the anticipatory aspects of postural control. This study investigated APMs and CPMs of the head and hip of healthy young and older adults in the temporal vicinity of physical and imagined forward raises of the dominant and non-dominant arm. When MI of the dominant arm was self-initiated, both age groups showed APM in the anteroposterior plane. When the self-initiated MI was of the non-dominant arm, only the older group showed anteroposterior APM. The older group did not show APM when an expected arm movement (or MI) was made to an external signal. This suggests an age-related deficit in coordinating postural preparation with external events. Only the older group showed mediolateral APM, and only for dominant arm MI, indicating sensitivity to potential perturbation to the weaker, non-dominant side of the body. Overall, the older group showed more anticipatory postural motion at the head. Systematic APM for manual MI suggests that MI training may be an effective intervention for anticipatory postural control. An integrated model of postural support for executed and imagined limb movements is suggested.

The role of spatial alignment in posture-cognition dual task interaction.

BACKGROUND: A range of cognitive tasks can interfere with postural control, particularly in older adults. In the case of spatial tasks, the spatial alignment between the task and postural control can incur dual-task costs separately from task load. It has been suggested that spatial tasks incur dual-task costs because accessing the visuospatial sketchpad component of working memory reduces the capacity to utilize external visual information for postural control. RESEARCH QUESTION: We investigated whether the spatial alignment between a cognitive and a postural control task can affect postural stability even when visual perception is not involved in either task and task load does not differ between aligned and non-aligned conditions. We predicted that any such effect would be greater in older people and in a more challenging stance. METHODS: Fifty healthy adults (27 aged 20-35, 23 aged 59-88) with no history of balance or cognitive difficulties performed a mental navigation task while standing in open or closed stance with eyes closed. The mental navigation task was presented in a reference plane that was either aligned or non-aligned to the horizontal reference plane in which the posture control system controlled the position of the body's center of gravity. Task performance was measured as accuracy and response time and postural sway as anteroposterior (AP) and mediolateral (ML) sway velocity. RESULTS: The older group were less accurate in the mental navigation task, and both groups had higher AP and ML sway velocity in closed stance. When standing in the more challenging stance, the older group had higher AP sway velocity while performing the mental navigation task in the non-aligned than the aligned reference plane condition. SIGNIFICANCE: The spatial configuration compatibility between a cognitive task and postural control can affect postural stability even when visual information is not being used for either task and task load is unchanged.

Incomplete inhibition of central postural commands during manual motor imagery.

Imagined movements exhibit many of the behavioral and neurophysiological characteristics of executed actions. As a result, they are considered simulations of physical actions with an inhibition mechanism that suppresses overt movement. This inhibition is incomplete, as it does not block autonomic preparation, and it also does not effectively suppress postural adjustments planned in support of imagined movements. It has been suggested that a central inhibition command may fail to suppress postural adjustments because it may not have access to afference-based elaborations of the postural response that occur downstream of central motor planning. Here, we measured changes in the postural response associated with imagining manual reaching movements under varying levels of imagined loading of the arm. We also manipulated stance stability, and found that postural sway reduced with increased (imagined) arm loading when imagining reaching movements from the less stable stance. As there were no afferent signals associated with the loading constraint, these results suggest that postural adjustments can leak during motor imagery because the postural component of the central motor plan is itself not inhibited effectively.

Sub-processes of working memory in the N-back task: an investigation using ERPs.

OBJECTIVE: The N-back task is frequently used in working memory studies. N-parameters allow experimental psychologists to analyze the sub-processes of N-back tasks in addition to general processing. However, previous imaging studies have not closely scrutinized these sub-processes. In the current study, three sub-processes in the N-back task were proposed using a logical task analysis: matching, replacement and shift. Domain-specific lateralization in spatial and verbal working memory was investigated in terms of this model. METHODS: This model was tested with two ERP experiments during N-back tasks, one conceptual (top-down) and one data-driven (bottom-up). RESULTS: Domain-specific lateralization was observed as predicted in the shift sub-process of the conceptual task and in the replacement sub-process of the data-driven task. Match-specific lateralization was also found. CONCLUSIONS: The results support our three-sub-process model of the N-back task and our hypothesis that replacement is a data-driven process with a posterior locus whereas shift is a more conceptual process with a more frontal locus. SIGNIFICANCE: The proposed model correctly predicted ERP patterns in conceptual and data-driven N-back tasks and is potentially useful in understanding the neurophysiologic basis of N-back task performance. The similarity between match- and domain-specific lateralization in N-back tasks raised several issues for further investigation.