Implicit learning may be shown by improvements in motor performance, which occur unconsciously with practice and are typically restricted to the task that was practiced. The purpose of this study was to examine behaviorally relevant brain activation associated with change in motor behaviour during sequence-specific motor learning of a perceptuomotor continuous tracking (CT) task in middle-aged adults. To gain further insight into the neural structures associated with change in motor behaviour, overall improvement in tracking (root mean square error; RMSE) was decomposed into two components – temporal precision and spatial accuracy. A group of middle-aged healthy individuals performed the CT task, which contains repeated and random segments for seven days. Functional magnetic resonance imaging (fMRI) data was collected on the first and seventh day while the participants performed the task. To assess behaviorally relevant changes in the blood oxygenation level dependent (BOLD) response associated with individual sequence-specific tracking performance, separate statistical images were created for each participant and weighted by the difference score between repeated and random performance for days 1 and 7. On Day 7 the resultant group statistical fMRI image demonstrated a positive correlation between RMSE difference score and bilateral cerebellar activation (lobule VI). In addition, individuals who showed greater sequence-specific temporal precision demonstrated increased activation in the precentral gyrus, middle occipital gyrus and putamen of the right hemisphere and the thalamus, cuneus and cerebellum of the left hemisphere. In the present study, behavioral performance was associated with neural correlates of individual variation in motor learning that characterized the ability to implicitly learn a sequence-specific CT task.

Several studies have shown that a light fingertip touch on a stable surface reduces body sway for individuals standing with their eyes closed even when touch forces are too low to offer mechanical support. It has been proposed that this is due to the availability of sway-relevant sensory feedback from the hand compensating for lost vision. Recently, we revealed modulation of cortical sensory transmission of information from the hand depending on the task (e.g. relevant or not relevant to balance control). Of interest in the present study is the potential origin of task-specific modulation of cortically evoked sensory potentials linked to balance control. We aimed to investigate the role of the prefrontal cortex by temporarily suppressing this region and observing differences in cortical events. Continuous θ-burst stimulation was applied to either the prefrontal cortex or a control stimulation site before balance testing. During balance testing, individuals stood in tandem on a force plate with their eyes closed while lightly touching a stable surface or a sway-referenced surface with the index finger. Throughout testing, the median nerve was stimulated and electroencephalography was used to measure somatosensory-evoked potentials. As expected, the availability of stable light touch reduced the medial–lateral centre of pressure sway. Importantly, in the present study, there was a loss of task-related P200 modulation at FCZ following stimulation of the prefrontal cortex. The present findings support the hypothesis that the prefrontal cortex may serve to regulate task-related sensory reweighting of haptic information that may be used during the control of standing balance.

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Connections between the cerebellum and the cortex play a critical role in learning and executing complex behaviours. Dual-coil transcranial magnetic stimulation (TMS) can be used non-invasively to probe connectivity changes between the lateral cerebellum and motor cortex (M1) using the motor evoked potential as an outcome measure (cerebellar-brain inhibition, CBI). However, it gives no information about cerebellar connections to other parts of cortex. We used electroencephalography (EEG) to investigate whether it was possible to detect activity evoked in any areas of cortex by single-pulse TMS of the cerebellum (cerebellar TMS evoked potentials, cbTEPs). A second experiment tested if these responses were influenced by the performance of a cerebellar-dependent motor learning paradigm. In the first series of experiments, TMS was applied over either the right or left cerebellar cortex, and scalp EEG was recorded simultaneously. Control conditions that mimicked auditory and somatosensory inputs associated with cerebellar TMS were included to identify responses due to non-cerebellar sensory stimulation. We conducted a follow-up experiment that evaluated whether cbTEPs are behaviourally sensitive by assessing individuals before and after learning a visuomotor reach adaptation task. A TMS pulse over the lateral cerebellum evoked EEG responses that could be distinguished from those caused by auditory and sensory artefacts. Significant positive (P80) and negative peaks (N110) over the contralateral frontal cerebral area were identified with a mirrored scalp distribution after left vs. right cerebellar stimulation. The P80 and N110 peaks were replicated in the cerebellar motor learning experiment and changed amplitude at different stages of learning. The change in amplitude of the P80 peak was associated with the degree of learning that individuals retained following adaptation. Due to overlap with sensory responses, the N110 should be interpreted with caution. Cerebral potentials evoked by TMS of the lateral cerebellum provide a neurophysiological probe of cerebellar function that complements the existing CBI method. They may provide novel insight into mechanisms of visuomotor adaptation and other cognitive processes.