Performance of certain cognitive tasks either during physical load or in rest pauses between boosts might lead to slowing of muscle fatigue and fatigue related decline in performance. Seventeen right-handed healthy volunteers (age 24±1.4, 8 males) participated in this study, aiming to investigate the effect of the level of the cognitive information processing -1) passive perception of audio stimuli, 2) active stimuli discrimination, 3) active stimuli discrimination following motor response -on motor task performance (handgrip test 30% and 7% of MVC) and muscle fatigue development. Cognitive tasks show the following effects on motor work: i) Perceived fatigue during 30 % MVC (fatiguing) condition developed slower if participant pressed button in response to deviant acoustic stimuli, as compared to passive listening. Counting task, an active task without motor component, took the intermediate position and did not differ significantly from two other cognitive tasks. ii) MVC after 30% MVC (fatiguing) condition tended to decrease stronger when accompanied with passive listening in comparison with both active tasks. iii) Motor task performance during 30% MVC (fatiguing) condition was better for active cognitive task with motor component than for passive task. Active task without motor component took the intermediate position and did not differ significantly from both the other cognitive tasks.
Muscle load can affect the performance of concurrent cognitive task. This effect is often explained by limited resources in the voluntary attention system. To examine whether earlier stages of cognitive information processing might be affected, we recorded the mismatch negativity component (MMN) of the auditory event-related brain potential before, during and after sustained handgrip at 7 and 30% of maximal voluntary contraction. MMN is an index of automatic detection of a deviating auditory event. MMN was not affected by force level. However, its amplitude at fronto-central sites decreased during the fatiguing 30% contraction, while it tended to increase during the light 7% work. Thus, muscle fatigue may affect auditory information processing at preattentive and preconscious stages, which could modify cognitive performance.
Mismatch negativity (MMN) is a component of auditory evoked potentials associated with rare changes in acoustic stimulation. Mismatch negativity is usually interpreted as an automatic response from a "changes detector" based on comparison of an incoming stimulus and the representation of preceding stimulation in memory. However, some investigators take the view that mismatch negativity is explained by simpler processes, associated with neuronal refractoriness. The existence of "genuine" mismatch negativity was confirmed, though the question of the contribution of refractoriness to traditional mismatch negativity remained open. The present study uses an experimental design allowing the hypothetical sources of mismatch negativity to be discriminated. A contribution to mismatch negativity associated with neuronal refractoriness was demonstrated; this decreased with increases in the probability of presentation of a deviant stimulus and became negligible at a probability of 15%. Thus, classically interpretable mismatch negativity can be obtained either by using a method excluding the contribution of refractoriness or by using "safe" deviant stimulus presentation probabilities.
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