Movement timing in the sub-second range engages a brain network comprising cortical and sub-cortical areas. The present study aims at investigating the functional significance of the left dorsolateral premotor cortex (dPMC) for precise movement timing as determined by sensorimotor synchronization and rhythm reproduction. To this end, 18 healthy volunteers performed an auditorily paced synchronization-continuation task with the right hand. A simple reaction time task served as control condition. Transcranial direct current stimulation (tDCS) was applied over the left dPMC in order to modulate cortical excitability either with anodal or cathodal polarity or as sham stimulation. TDCS was applied for 10 minutes, respectively on separate days. For the continuation task the analysis revealed significantly smaller inter-tap intervals (ITIs) following cathodal tDCS suggesting movement hastening as well as a trend towards larger ITIs following anodal stimulation suggesting movement slowing. No significant effect was found following sham stimulation. Neither for synchronization nor for reaction time tasks significant polarity-specific effects emerged. The data suggest the causal involvement of the dPMC in temporally precisereproduction of isochronous rhythms rather than sensorimotor synchronization. The present findings support the hypothesis that different cortical brain areas within the motor-control-network distinctively contribute to movement timing in the sub-second range.

For the seemingly effortless acquisition of new motor skills, a distributed network of cortical and subcortical structures is required. While a specific significance of the primary motor cortex (M1) for implicit motor sequence learning has been highlighted, the premotor cortex (PMC) has been related to consolidation of the newly learned sequence. To gain more insight into the contribution of the PMC to implicit sequence learning and early consolidation transcranial direct current stimulation (tDCS) was applied to the left PMC. In total 36 healthy right-handed volunteers (age: 24.0 ± 0.4 years, 18 male) participated in the study. Half of them received anodal, cathodal or sham tDCS prior to motor learning (experiment 1) while the other half received tDCS during learning (experiment 2). Stimulation duration was ten minutes, respectively. To induce implicit motor sequence learning a serial reaction time task (SRTT) with a repetitive fixed sequence interleaved by a random pattern was employed. Reaction times (RT) were determined separately for random and sequential trials at baseline (t1), end of acquisition (t2), and after presentation of an interfering random pattern (t3) in order to estimate consolidation of the trained sequence. In both experiments, at t2, facilitation of RT during sequential as compared to random trials was found in the sham condition indicating sequence learning. For active tDCS at t2 RT did not significantly differ between random and sequential trials suggesting a non-specific facilitation of RT. At t3 cathodal tDCS applied prior to SRTT yielded significantly faster RT in sequential as compared to random trials suggesting reduced susceptibility to interference. The present data support the hypothesis that the left PMC is not involved in the acquisition of an implicitly learned motor sequence. Interestingly enough, cathodal tDCS applied prior to learning resulted in reduced susceptibility to an interfering pattern revealing evidence for the assumption that suppression of left PMC excitability is beneficial for early consolidation of an implicit motor sequence.

Transcranial direct current stimulation (tDCS) allows the non-invasive modulation of cortical excitability. Anodal tDCS is associated with an increase of cortical excitability, while cathodal tDCS yields its decrease. Beyond altered excitability, tDCS to the primary motor cortex (M1) has been proven to modulate motor performance, but effects considerably vary across participants. To further elucidate the indicative role of baseline performance on the impact of tDCS, we subdivided 72 participants after baseline reaction time recordings into fast and slow performers by median split. Subsequently, participants implicitly learned a motor sequence with the right hand using the serial reaction time task. M1 is assumed to contribute to motor sequence acquisition and early motor memory consolidation, while the premotor cortex (PMC) may be relevant for later phases of consolidation. In half of the participants, tDCS was applied to the left M1 and in the other half to the left PMC. Since tDCS effects also vary with respect to timing of stimulation, tDCS was applied either prior to or during motor sequence learning. Anodal vs. cathodal vs. sham tDCS was applied in three separate sessions. When tDCS was applied prior to learning, anodal M1 tDCS facilitated subsequent sequence acquisition. Most interestingly, this effect became evident in participants with slow baseline reaction times only. When tDCS was applied during learning, anodal M1 tDCS yielded an unspecific facilitation of reaction times – again in participants with slow baseline performance only. Cathodal and sham tDCS as well as PMC tDCS had no such effect. Fast performers did not benefit from tDCS possibly due to a ceiling effect. Beyond underpinning the relevance of M1 for initial motor sequence acquisition, the present results complement evidence that behavioural tDCS effects may strongly depend on the behavioural status quo at time of stimulation.

Motor learning is an essential skill allowing the acquisition of new movement patterns. Transcranial direct current stimulation (tDCS) has been shown to modulate neuronal excitability along with behavioural performance in a polarity-dependent manner. Besides polarity, the effects of tDCS on motor learning also vary with the timing of stimulation. In order to gain a better understanding regarding the optimal timing of tDCS application to modulate implicit motor sequence learning, motor-cortical tDCS was applied prior to and during training on a serial reaction time task (SRTT). The SRTT employs a fixed sequential pattern of button presses allowing the assessment of implicit motor sequence learning. A random pattern served as control condition. 36 healthy subjects were assigned to one of two experiments: tDCS was applied prior to (experiment 1) or during (experiment 2) SRTT training. Anodal vs. cathodal vs. sham tDCS was applied to the left primary motor cortex (M1) for ten minutes in a counterbalanced order. Reaction times of the right hand were measured at Baseline and after SRTT training (End of Acquisition (EoA)). Anodal tDCS prior to SRTT training yielded a beneficial effect on the acquisition of the motor sequence, i.e. reaction times decreased significantly from Baseline to EoA in the sequential pattern. Moreover, at EoA, reaction times were significantly faster following anodal as compared to cathodal tDCS. Reaction times of the random pattern were not differentially modulated by stimulation polarity indicating a sequence-specific effect. In contrast, tDCS applied during SRTT training did not differentially modulate the acquisition of the motor sequence. These results indicate that the timing of tDCS is a crucial parameter yielding distinct effects on implicit motor sequence learning. Anodal tDCS prior to SRTT training resulted in a facilitation emphasising a beneficial effect of increased left M1 excitability for the subsequent acquisition of a new motor sequence. In contrast, modulation of motor-cortical excitability by tDCS during SRTT training yielded no differential effects. This finding implies that tDCS effects may vary with the activation level during stimulation (rest vs. movement).

Motor learning results from practice but also between practice sessions. After skill acquisition early consolidation results in less interference with other motor tasks and even improved performance of the newly learned skill. A specific significance of the primary motor cortex (M1) for early consolidation has been suggested. Since synchronized oscillatory activity is assumed to facilitate neuronal plasticity, we here investigate alterations of motor-cortical oscillations by means of event-related desynchronization (ERD) at alpha (8-12 Hz) and beta (13-30 Hz) frequencies in healthy humans. Neuromagnetic activity was recorded using a 306-channel whole-head magnetoencephalography (MEG) system. ERD was investigated in 15 subjects during training on a serial reaction time task and 10 min after initial training. The data were compared with performance during a randomly varying sequence serving as control condition. The data reveal a stepwise decline of alpha-band ERD associated with faster reaction times replicating previous findings. The amount of beta-band suppression was significantly correlated with reduction of reaction times. While changes of alpha power have been related to lower cognitive control after initial skill acquisition, the present data suggest that the amount of beta suppression represents a neurophysiological marker of early cortical reorganization associated with motor learning. (C) 2014 IBRO. Published by Elsevier Ltd. All rights reserved.

For music and language processing, memory for relative pitches is highly important. Functional imaging studies have shown activation of a complex neural system for pitch memory. One region that has been shown to be causally involved in the process for nonmusicians is the supramarginal gyrus (SMG). The present study aims at replicating this finding and at further examining the role of the SMG for pitch memory in musicians. Nonmusicians and musicians received cathodal transcranial direct current stimulation (tDCS) over the left SMG, right SMG, or sham stimulation, while completing a pitch recognition, pitch recall, and visual memory task. Cathodal tDCS over the left SMG led to a significant decrease in performance on both pitch memory tasks in nonmusicians. In musicians, cathodal stimulation over the left SMG had no effect, but stimulation over the right SMG impaired performance on the recognition task only. Furthermore, the results show a more pronounced deterioration effect for longer pitch sequences indicating that the SMG is involved in maintaining higher memory load. No stimulation effect was found in both groups on the visual control task. These findings provide evidence for a causal distinction of the left and right SMG function in musicians and nonmusicians.

Objectives: Motor learning occurs during practice but also between practice sessions. A specific significance of the primary motor cortex (M1) for early consolidation has been suggested. We here investigate alterations of motor-cortical oscillations associated with acquisition and early consolidation of a newly learned motor sequence.

Synchronized oscillatory activity at alpha (8-12 Hz) and beta (13-30 Hz) frequencies plays a key role in motor control. Nevertheless, its exact functional significance has yet to be solved. Transcranial alternating current stimulation (tACS) allows the frequency-specific modulation of ongoing oscillatory activity. The goal of the present study was to investigate the effect of 10 and 20 Hz tACS over left primary motor cortex (M1) on motor functions and cortical excitability in healthy subjects. To this end, tACS was applied for 10 min. Sham stimulation served as control condition. Movement speed and accuracy of the right hand were assessed in 15 right-handed subjects before and after (0,30 and 60 min) tACS of M1. Cortical silent period (CSP) and motor evoked potentials (MEPs) were determined as measures of M1 excitability. While 10 Hz tACS particularly increased movement variability, especially in tasks requiring internal pacing, 20 Hz tACS resulted in movement slowing. Behavioural effects occurred in distinct time windows. While 10 Hz effects developed over 30 min after stimulation, 20 Hz tACS effects were found immediately after stimulation. Following 10 Hz tACS these effects were significantly correlated with CSP duration, indicating interference with inhibitory pathways. The present findings suggest differential effects of stimulation frequency on motor behaviour and M1 excitability. (C) 2012 Elsevier B.V. All rights reserved.

Fragestellung: Synchronisierte oszillatorische Aktivität im Alpha- (8–12 Hz) und Beta- (13–30 Hz) Band spielt eine zentrale Rolle für die Bewegungssteuerung, wobei die genaue Bedeutung dieser Oszillationen noch ungeklärt ist. Mithilfe der transkraniellen Wechselstromstimulation (engl. transcranial alternating current stimulation, tACS) kann die oszillatorische Hirnaktivität in frequenzspezifischer Weise moduliert werden. Die vorliegende Studie untersuchte die Effekte von 10 und 20 Hz tACS über dem primären motorischen Areal (M1) auf motorische Funktionen und kortikale Exzitabilität.

Fragestellung: Im fortgeschrittenen Stadium von Morbus Parkinson (MP) kommt es zu Veränderungen der lokalen oszillatorischen Aktivität und der funktionellen Interaktion in einem zentralen Netzwerk der Bewegungssteuerung. Es ist jedoch unklar, ob diese bereits im Frühstadium der Erkrankung auftreten oder sich erst im Krankheitsverlauf entwickeln. Methode: Neuromagnetische Aktivität wurde bei 10 de novo Patienten, 10 Patienten mit medikamentöser Therapie und 10 gesunden Kontrollprobanden (KG) mithilfe eines 306-Kanal Ganzkopf-Magnetenzephalographen (MEG) untersucht. Die Ableitung erfolgte unter Ruhe und während einer isometrischen Halteaufgabe des stärker betroffenen Arms. Ergebnisse: Die Analyse der zerebro-muskulären Kohärenz (ZMK) im Betaband (13–30 Hz) zeigte – im Gegensatz zu fortgeschrittenen Stadien–keinen Unterschied zwischen den Gruppen. Die oszillatorische Aktivität des primären motorischen Kortex (M1) im Betaband war in beiden Konditionen bei den Patienten im Vergleich zur Kontrollstichprobe erhöht. In der KG zeigte sich während der Halteaufgabe eine Suppression der kontralateralen Hemisphäre. In der denovo Gruppe zeigte sich kein Unterschied zwischen den Hemisphären, während in der Gruppe der medizierten Patienten die ipsilaterale Hemisphäre stärker supprimiert wurde. Darüber hinaus korrelierte das Verhältnis zwischen ipsi- und kontralateraler Aktivierung signifikant mit der Krankheitsschwere. Schlussfolgerung: Die Abnahme der ZMK stellt kein Korrelat des initialen Erkrankungsstadiums dar. Die lokale oszillatorische Aktivität von M1 im Betaband ist allerdings bereits zu Beginn der Erkrankung erhöht. Mit zunehmender Krankheitsschwere entwickelt sich eine motor-kortikale Hemisphären-Asymmetrie, die sich ausschließlich während der Bewegungsausführung zeigt. Ein Kennzeichen des Frühstadiums von MP scheint somit die verminderte Fähigkeit von M1 zu sein, sich während der Bewegungsausführung von pathologisch verstärkten Oszillationen zu entkoppeln.

Key points Parkinson's disease (PD) is a common movement disorder due to dopaminergic denervation of the basal ganglia. It is characterized by exaggerated oscillatory activity within central motor‐control loops, while cerebro‐muscular coherence is reduced at frequencies below 30 Hz. So far, studies investigating the neurophysiological alterations of PD have focused on patients with advanced PD. It remains open to what extent changes of oscillatory activity might occur at early disease stages, representing a characteristic feature of the disease. Using magnetoencephalography we show that cerebro‐muscular coherence is unaffected in early PD while beta band oscillations of bilateral primary sensori‐motor cortices are already increased at the earliest stages of PD and, as the disease progresses, evolve a hemispheric imbalance associated with movement execution. Abstract Pathophysiological changes in basal ganglia‐thalamo‐cortical circuits are well established in idiopathic Parkinson's disease (PD). However, it remains open whether such alterations already occur at early stages representing a characteristic neurophysiological marker of PD. Therefore, the present study aims at elucidating changes of synchronised oscillatory activity in early PD patients. In this study, we performed whole‐head magnetoencephalography (MEG) in a resting condition and during steady state contraction of the more severely affected forearm in 10 drug–naive, de novo patients, in 10 early‐stage patients with chronic medication and in 10 age‐matched control subjects. While cortico‐muscular coherence (CMC) did not differ between groups, patients showed increased sensori‐motor cortical power at beta frequency (13–30 Hz) during rest as well as during isometric contraction compared to controls. In healthy control subjects the power of the contralateral hemisphere was significantly suppressed during isometric contraction. By contrast, both hemispheres were activated equally strongly in de novo patients. In medicated patients, the pattern was found to be reversed. Contralateral beta power was significantly correlated with motor impairment during isometric contraction but not during rest. The present results suggest that the reduced ability of the primary motor cortex to disengage from increased beta band oscillations during the execution of movements is an early marker of PD.

Fragestellung: Der zeitlichen Steuerung von Bewegungen liegt auf zentraler Ebene ein zerebello-thalamo-kortikales Netzwerk zugrunde. Der posteriore parietale Kortex (PPC) scheint hierbei eine zentrale Rolle zu spielen. Seine genaue Funktion ist jedoch unklar: Neben der Bewegungsantizipation könnte er der Integration multisensorischer Informationen dienen.

Synchronizing one's own movement with respect to a temporally predictable structure of events appears in various contexts of life. A precise coordination of perception and action is herefore required. Though synchronization with respect to an auditory pacing signal seems to be simple, a systematic bias occurs: Typically, the tap precedes the pacing signal by several milliseconds despite the subjective impression of synchrony. Since it has been argued that this so-called negative asynchrony might be due to sensory processing rather than to a systematic bias in the motor system, the present study aims at elucidating whether the same bias occurs in a sensory discrimination task. Additionally, the study aims at investigating whether discrimination abilities might vary with synchronization abilities. To this end, we investigated 60 healthy, right-handed subjects differing according to their musical experience. We observed superior synchronization abilities of drummers in comparison to professional and amateur pianists, singers and non-musicians. In all subjects we found an order-dependent bias of cross-modal discrimination: The discrimination threshold was higher for a tactile stimulus preceding an auditory one than vice versa. This indicates a higher error tolerance for this order of stimulation which is comparable to the synchronization bias. The drummers with the most accurate synchronization performance showed the lowest discrimination threshold. These data imply that synchronization performance does not only rely on motor but also on perceptual components. A behavioural advantage in synchronization tasks is accompanied by a perceptual advantage or maybe even caused by it.