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The objective of the present study was to identify the origin(s) of ageing-related behavioural slowing in sensorimotor tasks. For this aim, event-related potentials (ERPs) were analysed at 64 electrodes to evaluate the strength and timing of different stages of information processing in the brain. Electrophysiological indices of stimulus processing, sensorimotor integration/response selection and motor-related processing were used to compare the processing speed of young (n = 13, mean age = 22.5 years) and older adults (n = 14, mean age = 58.3 years) in simple- and choice-reaction tasks presented in two modalities, auditory and visual. The behavioural results showed significant ageing-related slowing, but only in the choice-reaction task. The quantification of separate central processing stages, in combination with advanced ERP methodology, helped to reveal that this slowing did not originate from the early processes of stimulus processing and response selection. Instead, it was produced by slower activation patterns over the contralateral motor cortex underlying response generation. It is concluded that ageing is accompanied by a functional dysregulation of motor cortex excitability during sensorimotor processing, with this deficit becoming progressively evident with greater task complexity.

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Sleep has been shown to promote the generation of explicit knowledge as indicated by the gain of insight into previously unrecognized task regularities. Here, we explored whether this generation of explicit knowledge depends on pre-sleep implicit knowledge, and specified the differential roles of slow-wave sleep (SWS) vs. rapid eye movement (REM) sleep in this process. Implicit and explicit knowledge (insight) related to a hidden regularity were assessed in an associative motor-learning task (number reduction task, NRT), which was performed in two sessions (initial practice and retest) separated by 3 h of either early-night sleep, rich in SWS, or of late-night sleep, rich in REM sleep. About half of the participants developed signs of implicit rule knowledge (i.e., speeded reaction times for responses determined by the hidden regularity) at initial practice preceding early or late sleep. Of these, half developed explicit knowledge across early-night sleep, significantly more than across late-night sleep. In contrast, late-night subjects preferentially remained on the level of implicit rule knowledge after sleep. Participants who did not develop implicit knowledge before sleep had comparable rates of transition to implicit or explicit knowledge across early and late sleep. If subjects gained explicit knowledge across sleep, this was associated with lower amounts of REM sleep, specifically in the late-night group. SWS predominant during the early night may restructure implicit memory representations in a way that allows creating an explicit representation afterward, whereas REM sleep in the late night appears to stabilize them in their implicit form.

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A time-frequency decomposition was applied to rare target and frequent non-target event-related potentials (ERPs) elicited in an oddball condition to assess whether multiple functional components occur in the P300 latency range. The wavelet transform (WT) was used because it allows capture of simultaneous or partly overlapping components in ERPs without loosing their temporal relationships. The application of a four-octave quadratic B-spline wavelet transform at the level of single-sweep data allowed us to obtain new information and revealed the presence of separate events during P300 development. Several delta, theta, and alpha frequency components in the P300 latency range differed between target and non-target processing. These findings indicate that P300 is composed of multiple functional components and that the WT method is of use for the study of P300 functional correlates more precisely.

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