The effect of attentional and motor demands on motor overflow production in older adults.

Patricia Addamo
Experimental Neuropsychology Research Unit, School of Psychology, Psychiatry & Psychological Medicine, Monash Univer

*Maree Farrow
Alzheimer's Australia

*Kate Hoy
Experimental Neuropsychology Research Unit, School of Psychology, Psychiatry & Psychological Medicine, Monash University

*John Bradshaw
Experimental Neuropsychology Research Unit, School of Psychology, Psychiatry & Psychological Medicine, Monash University

*Nellie Georgiou-Karistianis
Experimental Neuropsychology Research Unit, School of Psychology, Psychiatry & Psychological Medicine, Monash University

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     Last modified: February 27, 2007

Abstract
Abstract
The purpose of this study was to systematically investigate how attentional and motor demands influence motor overflow production in both young adults and healthy older adults. Motor overflow is involuntary muscle activity that may coincide with voluntary movement and is thought to increase with old age. Seventeen young adults, aged 18-35, and 17 older adults, aged 60-80 years, performed a finger pressing task and exerted a percentage of their maximal force output with one hand while overflow was recorded in the passive hand. Required target force output was either 33% or 66% of maximal force and for half the trials was performed with the participants? non-dominant hand. Attention was manipulated by presenting a tactile stimulus to one or both hands for certain trials. Results indicated that older adults exhibited greater overflow compared to their younger counterparts. Although both age groups displayed greater overflow at the lower target force, this effect was exacerbated in older adults. Furthermore, overflow in older adults, but not young adults, was greater when attention was directed to one or both hands during task performance. No significant intermanual asymmetry in overflow production was found for either age group. Importantly, task performance measures suggested that both age groups were able to effectively perform the task, although older adults were significantly more variable. When attention and motor demands were imposed there was greater variability in both task performance and level of overflow production. Collectively, the increase in motor overflow in old age has been interpreted as evidence of possible bilateral cortical activation which may be influenced by increased task demands. In order to compensate for age-related brain deterioration and perform comparatively to younger adults, older adults may recruit an increased cortical network of brain regions to meet task demands.