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Increasing evidence suggests a considerable role of pre-movement beta bursts for motor control and its impairment in Parkinson's disease. However, whether beta bursts occur during precise and prolonged movements and if they affect fine motor control remains unclear. To investigate the role of within-movement beta bursts for fine motor control, we here combine invasive electrophysiological recordings and clinical deep brain stimulation in the subthalamic nucleus in 19 patients with Parkinson's disease performing a context-varying task that comprised template-guided and free spiral drawing. We determined beta bursts in narrow frequency bands around patient-specific peaks and assessed burst amplitude, duration, and their immediate impact on drawing speed. We reveal that beta bursts occur during the execution of drawing movements with reduced duration and amplitude in comparison to rest. Exclusively when drawing freely, they parallel reductions in acceleration. Deep brain stimulation increases the acceleration around beta bursts in addition to a general increase in drawing velocity and improvements of clinical function. These results provide evidence for a diverse and task-specific role of subthalamic beta bursts for fine motor control in Parkinson's disease; suggesting that pathological beta bursts act in a context dependent manner, which can be targeted by clinical deep brain stimulation. How movement speed is neurally modulated remains poorly understood. Here, the authors recorded invasive brain signals in Parkinson's disease patients during drawing and deep brain stimulation, showing a context-dependent relationship between reductions of movement acceleration and dynamic activity of the basal ganglia. [ABSTRACT FROM AUTHOR]

Essential tremor is a common neurological disorder, characterised by involuntary shaking of a limb. Patients are usually treated using medications which have limited effects on tremor and may cause side-effects. Surgical therapies are effective in reducing essential tremor, however, the invasive nature of these therapies together with the high cost, greatly limit the number of patients benefiting from them. Non-invasive therapies have gained increasing traction to meet this clinical need. Here, we test a non-invasive and closed-loop electrical stimulation paradigm which tracks peripheral tremor and targets thalamic afferents to modulate the central oscillators underlying tremor. To this end, 9 patients had electrical stimulation delivered to the median nerve locked to different phases of tremor. Peripheral stimulation induced a subtle but significant modulation in five out of nine patients—this modulation consisted mainly of amplification rather than suppression of tremor amplitude. Modulatory effects of stimulation were more pronounced when patient's tremor was spontaneously weaker at stimulation onset, when significant modulation became more frequent amongst subjects. This data suggests that for selected individuals, a more sophisticated control policy entailing an online estimate of both tremor phase and amplitude, should be considered in further explorations of the treatment potential of tremor phase-locked peripheral stimulation. [ABSTRACT FROM AUTHOR]

Low-frequency oscillations in the basal ganglia are prominent in patients with Parkinson's disease off medication. Correlative and more recent interventional studies potentially implicate these rhythms in the pathophysiology of Parkinson's disease. However, effect sizes have generally been small and limited to bradykinesia. In this study, we investigate whether these effects extend to rigidity and are maintained in the on-medication state. We studied 24 sides in 12 patients on levodopa during bilateral stimulation of the STN at 5, 10, 20, 50, 130 Hz and in the off-stimulation state. Passive rigidity at the wrist was assessed clinically and with a torque-based mechanical device. Low-frequency stimulation at ≤20 Hz increased rigidity by 24 % overall ( p = 0.035), whereas high-frequency stimulation (130 Hz) reduced rigidity by 18 % ( p = 0.033). The effects of low-frequency stimulation (5, 10 and 20 Hz) were well correlated with each other for both flexion and extension ( r = 0.725 ± SEM 0.016 and 0.568 ± 0.009, respectively). Clinical assessments were unable to show an effect of low-frequency stimulation but did show a significant effect at 130 Hz ( p = 0.002). This study provides evidence consistent with a mechanistic link between oscillatory activity at low frequency and Parkinsonian rigidity and, in addition, validates a new method for rigidity quantification at the wrist. [ABSTRACT FROM AUTHOR]

Could task performance be constrained by our ability to fully engage necessary neural processing through effort of will? The StartReact phenomenon suggests that this might be the case, as voluntary reaction times are substantially reduced by loud sounds. Here, we show that loud auditory stimulation can also be associated with an improvement in the force and speed of force development when 18 healthy subjects are repeatedly asked to make a maximal grip as fast and as strongly as possible. Peak grip force was increased by 7.2 ± 1.4% (SEM) ( P < 0.0001), and the rate of force development was increased by 17.6 ± 2.0% ( P ≪ 0.00001), when imperative visual cues were accompanied by a loud auditory stimulus rather than delivered alone. This implies that loud auditory stimuli may allow motor pathways to be optimised beyond what can be achieved by effort of will alone. [ABSTRACT FROM AUTHOR]

We investigated the neural correlates of dual task performance using EEG coherence as a measure of the functional coupling between cortical regions. Nine healthy participants performed a rhythmical movement with the right hand and an isometric contraction with the left hand, either initiated simultaneously or successively. EEG data revealed that dual task performance was associated with stronger coherence in left hemispheric and mesial areas than the sum of the tasks performed separately in the beta (>12–30 Hz), but not alpha (8–12 Hz), band. This effect was more pronounced when the two assignments were initiated simultaneously, as opposed to successively. The data demonstrate that the pattern of cortico-cortical coupling during bimanual actions is not just the sum of that associated with its component parts, but is increased according to coordinative demands and processing load. [ABSTRACT FROM AUTHOR]

Working memory is implicated in various higher-order cognitive operations. We hypothesized that the availability of a temporal representation in working memory would limit the extent of cortico-cortical coupling necessary to undertake a self-paced rhythmic movement. To this end we examined modulations in cortico-cortical interactions as determined by EEG coherence during a delay interval and subsequent movement reproduction. Right hand movement was initially paced by a metronome beat every 0.9 s, followed by a delay interval, after which hand movement was repeated in an unpaced manner. Movement reproduction after a long (22.5 s, corresponding to 25 movement cycles) compared to a short (5.4 s, corresponding to 6 movement cycles) delay interval was associated with an increased degree of functional coupling in the beta frequency band (12–30 Hz) of the left (movement-driving) hemisphere (F3-FC3, F3-C3 and F3-P3 connections) as well as mesial regions (FCz-FC3, FCz-C3 and Cz-FC3 connections) even though overall behavioral characteristics were not influenced. In addition, analysis of the EEG coherence in the delay period revealed a bilateral frontal network (F3-F4, F3-FC4, F4-FC3 and FC3-FC4 connections). Activity in the latter tended to be synchronized in the theta band (4–8 Hz) and was significantly less strong at 22.5 s than 5.4 s. These data suggest that working memory may be partly subserved by synchronization in a bilateral frontal network and may provide an intrinsic contextual influence that shapes the pattern of cortico-cortical interaction during a given task. [ABSTRACT FROM AUTHOR]

Cognitive regulation enables a subject to plan actions according to context and to respond in a flexible manner to environmental conditions. This implies that foreknowledge about a change in system configuration will trigger preparatory activity in anticipation of the impending transformation. In the present study, we evaluate a unimanual task under two performance conditions that affected the cognitive context, and examine modulations in cortico-cortical interactions as determined by EEG coherence. The right hand movement was performed in an experimental paradigm that necessitated in some trials a voluntary and predictable switch towards a left hand movement, whereas in other trials no switch was required and movement of the right hand continued. The data showed that execution of the right hand movement was associated with an increased degree of task-related coherence in the alpha frequency band (8–12 Hz) in the switching as compared to the no switching condition, and this was most apparent for fronto-parietal connections of the movement-driving (left) as well as for the primed (right) hemisphere. For the primed hemisphere, we observed that the information flow was driven from the F4 electrode overlying the prefrontal area, which suggests that anticipatory preplanning occurred. These data indicate that higher-order cognitive operations bias cortico-cortical interactions in respect of an upcoming switch of the task settings between effectors by recruiting neural resources proactively. Dynamic adjustments in the alpha band suggest that low frequency activity is a characteristic of distributed information processing related to movement planning. [ABSTRACT FROM AUTHOR]