Working memory load reduces corticospinal suppression to former go and trained no-go cues.

Environmental cues associated with an action can prime the motor system, decreasing response times and activating motor regions of the brain. However, when task goals change, the same responses to former go-associated cues are no longer required and motor priming needs to be inhibited to avoid unwanted behavioural errors. The present study tested whether the inhibition of motor system activity to presentations of former go cues is reliant on top-down, goal-directed cognitive control processes using a working memory (WM) load manipulation. Applying transcranial magnetic stimulation over the primary motor cortex to measure motor system activity during a Go/No-go task, we found that under low WM, corticospinal excitability was suppressed to former go and trained no-go cues relative to control cues. Under high WM, the cortical suppression to former go cues was reduced, suggesting that the underlying mechanism required executive control. Unexpectedly, we found a similar result for trained no-go cues and showed in a second experiment that the corticospinal suppression and WM effects were unrelated to local inhibitory function as indexed by short-interval intracortical inhibition. Our findings reveal that the interaction between former response cues and WM is complex and we discuss possible explanations of our findings in relation to models of response inhibition.

Youth marathon runners and race day medical risk over 26 years.

OBJECTIVE: To report the number of marathon finishers younger than 18 years and race day medical encounters at the same site and to compare them with adult finishers. DESIGN: Retrospective cohort study. SETTING: Urban 42-km road race. PARTICIPANTS: Twin Cities Marathon finishers. ASSESSMENT OF RISK FACTORS: The race records from 1982 to 2007 were assessed for finishers younger than 18 years to determine the number of finishers and medical encounters, incidence of race-related medical encounters, and type and severity of medical problems. MAIN OUTCOME MEASURES: Age group marathon finishers and medical encounters. RESULTS: Three hundred ten marathon (225 boys and 85 girls) aged 7 to 17 years finished the race with times ranging from 2:53:22 to 6:10:00. There were 4 medical encounters (minor in nature and required no intervention beyond a short period of rest) for an incidence of 12.9 per 1000 finishers. The odds ratio for youth compared with adult finish line medical encounters was 0.52 (P = 0.2658; 95% confidence interval, 0.19-1.39). CONCLUSIONS: Three hundred ten youth marathon successfully finished Twin Cities Marathon over 26 years with only 4 requiring post-race medical evaluations. The relative risk of requiring acute race day medical attention was less than, but not statistically different from, adult finishers.