Abstract
Older adults exhibit more bilateral motor cortical activity during unimanual task performance than young adults. Interestingly, a similar pattern is seen in young adults with reduced hand dominance. However, older adults report stronger hand dominance than young adults, making it unclear how handedness is manifested in the aging motor cortex. Here, we investigated age differences in the relationships between handedness, motor cortical organization, and interhemispheric communication speed. We hypothesized that relationships between these variables would differ for young and older adults, consistent with our recent proposal of an age-related shift in interhemispheric interactions. We mapped motor cortical representations of the right and left first dorsal interosseous muscles using transcranial magnetic stimulation (TMS) in young and older adults recruited to represent a broad range of the handedness spectrum. We also measured interhemispheric communication speed and bimanual coordination. We observed that more strongly handed older adults exhibited more ipsilateral motor activity in response to TMS; this effect was not present in young adults. Furthermore, we found opposing relationships between interhemispheric communication speed and bimanual performance in the two age groups. Thus, handedness manifests itself differently in the motor cortices of young and older adults and has interactive effects with age.
Highlights
One of the most robust findings in the cognitive neuroscience of aging literature is the more diffuse, bilateral, task-related brain activity seen in older versus young adults during the performance of cognitive tasks [1,2,3]
In order to better understand the pattern of bilateral activation in the motor cortex in older adults, it is important to take into account other factors that might be associated with bilateral motor cortical activity
The Poisson distribution is used for evaluating count data where high frequency events are relatively rare [52], as we found to be the case with the occurrence of ipsilateral Motor-evoked potentials (MEPs)
Summary
One of the most robust findings in the cognitive neuroscience of aging literature is the more diffuse, bilateral, task-related brain activity seen in older versus young adults during the performance of cognitive tasks [1,2,3]. The literature is mixed regarding whether additional activity in the motor cortex during motor tasks is associated with better performance for older adults [4,5], or has deleterious effects on behavior [8]. In order to better understand the pattern of bilateral activation in the motor cortex in older adults, it is important to take into account other factors that might be associated with bilateral motor cortical activity. One such factor is handedness; young adults who report low levels of hand dominance show more bilateral brain activation when performing unimanual actions [9,10] and have more bilateral motor cortical representations [11]. Handedness is interesting to investigate in older adults given that hand preference differs in young and older adults and this may influence motor cortical representations
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