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Right parietal cortex has recently been linked to the temporal resolution of attention. We therefore sought to investigate whether disruption to right parietal cortex would affect attention to visual stimuli presented for brief durations. Participants performed a visual discrimination task before and after 10 minutes repetitive transcranial magnetic stimulation (1 Hz) to right or central parietal cortex as well as 20 minutes after the second block of trials. Participants reported the spatial frequency of a masked Gabor patch presented for a brief duration of 60, 120, or 240 ms. We calculated error magnitudes by comparing accuracy to a guessing model. We then compared error magnitudes to blocks with no stimulation, producing a measure of baselined performance. Baselined performance was poorer at longer stimulus durations after right parietal than central parietal stimulation, suggesting that right parietal cortex is involved in attention to briefly presented stimuli, particularly in situations where rapid accumulation of visual evidence is needed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Imagined movements are thought to simulate physical ones, with similar behavioral constraints and neurophysiological activation patterns and with an inhibition mechanism that suppresses movement execution. When upper body movements such as reaching with the arm are made from an upright stance, lower body and trunk muscles are also activated to maintain body posture. It is not clear to what extent parameters of imagined manual movements are sensitive to the postural adjustments their execution would necessitate, nor whether such postural responses are as effectively inhibited as the imagined movements themselves. We asked healthy young participants to imagine reaching movements of the arm while in upright stance, and we measured their self-reported movement times and postural sway during imagined movements. We manipulated mediolateral stance stability and the direction of arm movement (mediolateral or anteroposterior). Imagined arm movements were reportedly slower when subjects were standing in a mediolaterally less stable stance, and the body swayed more when arm movements were imagined in the direction of postural vulnerability. The results suggest that the postural state of the whole body, not just the involved limbs, informs trajectory planning during motor imagery and that measurable adjustments to body posture accompany imagined manual actions. It has been suggested that movement is suppressed during motor imagery by a premotor inhibitory mechanism operating at brain stem or spinal level. Any such inhibition must be incomplete because, for example, it does not eliminate autonomic arousal. Our results suggest that it also does not effectively suppress postural adjustments planned in support of imagined movements. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Physical and imagined movements show similar behavioral constraints and neurophysiological activation patterns. An inhibition mechanism is thought to suppress overt movement during motor imagery, but it does not effectively suppress autonomic or postural adjustments. Inhibitory processes and postural stability both deteriorate with age. Thus, older people's balance is potentially vulnerable to interference from postural adjustments induced by thoughts about past or future actions. Here, young and older adults stood upright and executed or imagined manual reaching movements. Reported arm movement time (MT) of all participants increased with target distance. Older participants reported longer MT than young participants when executing arm movements, but not when imagining them. Older adults' anteroposterior (AP) and mediolateral (ML) postural sway was higher than young adults' at baseline, but their AP sway fell below their baseline level during manual imagery. In contrast, young adults' AP sway increased during imagery relative to their baseline. A similar tendency to reduce sway in the ML direction was also observed in older adults during imagery in a challenging stance. These results suggest that postural response during manual motor imagery reverses direction with age. Motor imagery and action planning are ubiquitous tasks, and older people are likely to spend more time engaged in them. The shift toward restricting body sway during these tasks is akin to a postural threat response, with the potential to interfere with balance during activities of daily living. (PsycINFO Database Record [ABSTRACT FROM AUTHOR]