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The phenomenon of cross-limb transfer, in which unilateral strength training can result in bilateral strength gains, has recently been tested for ballistic movements. Performance gains associated with repetitive motor practice, and the associated transfer, occur within a few minutes. In this study, young and older adults were trained to perform ballistic abductions of their dominant (right) index finger as quickly as possible. Performance was assessed bilaterally before, during, and after this training. Both groups exhibited large performance gains in the right hand as a result of training (P < 0.001; young 84% improvement, older 70% improvement), which were not significantly different between groups (P = 0.40). Transcranial magnetic stimulation revealed that the performance improvements were accompanied by increases in excitability, together with decreases in intracortical inhibition, of the projections to both the trained muscle and the homologous muscle in the contralateral limb (P < 0.05). The young group also exhibited performance improvements as a result of cross-limb transfer in the left (untrained) hand (P < 0.005), equivalent to 75% of the performance increase in the trained hand. In contrast, there were no significant performance gains in the left hand for the older group (P = 0.23). This was surprising given that the older group exhibited a significantly greater degree of mirror activity than the young group (P < 0.01) in the left first dorsal interosseus muscle (FDI) during right hand movements. Our findings suggest that older adults exhibit a reduced capacity for cross-limb transfer, which may have implications for motor rehabilitation programs after stroke.

We investigated how volitional contractions affect interhemispheric inhibition (IHI) from the active to the passive hemisphere. Younger and older adults isometrically contracted their dominant thumb (abductor pollicis brevis, APB) to various force targets. In ballistic contraction trials, transcranial magnetic stimulation (TMS) was administered very shortly after the onset of APB activity. In tonic contraction trials, TMS was delivered while the target force was maintained. In control trials both thumbs remained quiescent. In all trials, a test stimulus (TS) was directed to the APB hotspot in the non-dominant hemisphere (130% left APB resting motor threshold, RMT). In half the trials, a conditioning stimulus (130% right APB RMT) was applied to the APB hotspot in the dominant hemisphere 10 ms prior to the TS. Targeted ballistic contractions of the right APB were found to modulate (increase) IHI measured in the left APB, as previously reported for tonic contractions. Furthermore, the extent of the IHI increase was found to scale with the strength of the contralateral ballistic or tonic contraction. Less pronounced, but statistically significant, IHI increases were also observed in the left abductor digiti minimi and extensor carpi radialis during right APB contraction. For these muscles, however, the extent of the IHI modulation was independent of APB contraction strength. The capacity to modulate inhibition during contractions was unaffected by advancing age. During volitional actions, the ability to modulate IHI most adaptively in the homologous muscle of the resting limb may contribute to the prevention of mirror movements.

Infectious diseases (ID) specialists have played a major role in patient care, infection control, and antibiotic management for many years. With the rapidly changing nature of health care, it has become necessary for ID specialists to articulate their value to multiple audiences. This article summarizes the versatile attributes possessed by ID specialists and delineates their value to patients, hospitals, and other integral groups in the health care continuum.

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Abstract■ This study tested the postulation that change in the ability to modulate corticospinal excitability and inhibitory processes underlie age-related differences in response preparation and generation during tasks requiring either rapid execution of a motor action or actively withholding that same action. Younger (n = 13, mean age = 26.0 years) and older adults (n = 13, mean age = 65.5 years) performed an RT task in which a warning signal ( WS) was followed by an imperative signal (IS) to which participants were required to respond with a rapid flexion of the right thumb (go condition) or withhold their response (no-go condition). We explored the neural correlates of response preparation, generation, and inhibition using single-and paired-pulse TMS, which was administered at various times between WS and IS (response preparation phase) and between IS and onset of response-related muscle activity in the right thumb (response generation phase). Both groups exhibited increases in motorevoked potential amplitudes (relative to WS onset) during response generation; however, this increase began earlier and was more pronounced for the younger adults in the go condition. Moreover, younger adults showed a general decrease in shortinterval intracortical inhibition during response preparation in both the go and no-go conditions, which was not observed in older adults. Importantly, correlation analysis suggested that for older adults the task-related increases of corticospinal excitability and intracortical inhibition were associated with faster RT. We propose that the declined ability to functionally modulate corticospinal activity with advancing age may underlie response slowing in older adults. ■

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