Search

Transcranial evoked potentials (TEPs) measured via electroencephalography (EEG) are widely used to study the cortical responses to transcranial magnetic stimulation (TMS). Immediate transcranial evoked potentials (i-TEPs) have been obscured by pulse and muscular artifacts. Thus, the TEP peaks that are commonly reported have latencies that are too long to be caused by direct excitation of cortical neurons. In 25 healthy individuals, we recorded i-TEPs evoked by a single biphasic TMS pulse targeting the primary motor hand area (M1 HAND) or parietal or midline control sites. Sampling EEG at 50 kHz enabled us to reduce the duration of the TMS pulse artifact to a few milliseconds, while minor adjustments of the TMS coil tilt or position enabled us to avoid cranial muscular twitches during the experiment. We observed an early positive EEG deflection starting after approx. 2 ms followed by a series of superimposed peaks with an inter-peak interval of ∼1.1–1.4 ms in multiple electrodes surrounding the stimulated sensorimotor region. This multi-peak i-TEP response was only evoked by TMS of the M1 HAND region and was modified by changes in stimulation intensity and current direction. Single-pulse TMS of the M1 HAND evokes an immediate local multi-peak response at the cortical site of stimulation. Our results suggest that the observed i-TEP patterns are genuine cortical responses evoked by TMS caused by synchronized excitation of pyramidal neurons in the targeted precentral cortex. This notion needs to be corroborated in future studies, including further investigations into the potential contribution of instrumental or physiological artifacts. • Very early EEG responses to TMS have been obscured by artefacts. • We observed immediate transcranial evoked potentials (i-TEPs) from 2 ms after TMS. • The i-TEPs were composed of a slower positive deflection and high frequency peaks. • The i-TEPs were site-specific and only elicited by stimulation of M1. • The i-TEPs were modified by stimulation intensity and current direction. [ABSTRACT FROM AUTHOR]

• We tested the effects of a single bout of exercise or rest on rTMS-induced interference with motor memory consolidation. • rTMS targeting the primary motor cortex (M1) impeded offline performance changes for the resting group compared to sham. • A single bout of exercise counteracted the negative effects of rTMS on offline performance changes. • Acute exercise protects against retrograde interference from rTMS in a network comprising M1 and the corticospinal system. • Our results suggest that M1 and the corticospinal system mediate the effects of exercise on motor memory consolidation. Acute cardiovascular exercise can promote motor memory consolidation following motor practice, and thus long-term retention, but the underlying mechanisms remain sparsely elucidated. Here we test the hypothesis that the positive behavioral effects of acute exercise involve the primary motor cortex and the corticospinal pathway by interfering with motor memory consolidation using non-invasive, low frequency, repetitive transcranial magnetic stimulation (rTMS). Forty-eight able-bodied, young adult male participants (mean age = 24.8 y/o) practiced a visuomotor accuracy task demanding precise and fast pinch force control. Following motor practice, participants either rested or exercised (20 min total: 3 × 3 min at 90% VO 2peak) before receiving either sham rTMS or supra-threshold rTMS (115% RMT, 1 Hz) targeting the hand area of the contralateral primary motor cortex for 20 min. Retention was evaluated 24 h following motor practice, and motor memory consolidation was operationalized as overnight changes in motor performance. Low-frequency rTMS resulted in off-line decrements in motor performance compared to sham rTMS, but these were counteracted by a preceding bout of intense exercise. These findings demonstrate that a single session of exercise promotes early motor memory stabilization and protects the primary motor cortex and the corticospinal system against interference. [ABSTRACT FROM AUTHOR]

• During motor learning, movement outcomes inform the planning of future behaviour. • Humans assign different values to successful and unsuccessful movement outcomes. • Prefrontal theta oscillations are modulated during changes in consecutive outcomes. The history of our actions and their outcomes represent important information, informing choices and efficiently guiding future behavior. While unsuccessful (S−) outcomes are expected to lead to more explorative motor states and increased behavioral variability, successful (S+) outcomes are expected to reinforce the use of the previous action. Here, we show that humans attribute different values to previous actions during reinforcement motor learning when they experience S− compared to S+ outcomes. Behavioral variability after an S− outcome is influenced more by the previous outcome than after S+ outcomes. Using electroencephalography, we show that theta band oscillations of the prefrontal cortex are most prominent during changes in two consecutive outcomes, potentially reflecting the need for enhanced cognitive control. Our results suggest that S+ experiences 'overwrite' previous motor states to a greater extent than S− experiences and that modulations in neural oscillations in the prefrontal cortex play a potential role in encoding changes in movement variability state during reinforcement motor learning. [ABSTRACT FROM AUTHOR]

We investigated whether cortico-spinal excitability (CSE), a marker of synaptic plasticity, is associated with age-related differences in the consolidation of motor memory. Young and older participants practiced a visuomotor tracking task. Skill retention was assessed 8 and 24 hours after motor practice. Transcranial magnetic stimulation applied over the primary motor cortex at rest and during an isometric muscle contraction was used to assess absolute and normalized to baseline CSE at different points after practice. When skill performance was normalized to baseline level, both groups showed similar gains in acquisition, but the young group showed better retention 24 hours after practice. The young group also showed greater absolute CSE assessed during the isometric muscle contraction. Although young participants with greater absolute CSE showed better skill retention, it was the capacity to increase CSE after motor practice, and not absolute CSE, what was associated with skill retention in older participants. Older adults who have the capacity to increase CSE during motor memory consolidation show a better capacity to retain motor skills. [ABSTRACT FROM AUTHOR]