Changes in functional coupling patterns during bimanual task performance

Age-Related Development of Bilateral Coordination of the Upper Limbs in Children and Adolescents

Bilateral coordination of the upper limbs (UL) is important for activities of daily living and physical activities. Motor coordination improves from childhood through adolescence. However, age-coordination trajectories for bilateral UL movements are not well-established, and it is unclear if bimanual coordination develops slower than unilateral coordination. In this study we examined age-related changes in UL coordination from childhood to late adolescence. Typically-developing children (N = 29, aged 7-17 years) performed unilateral and bilateral, antiphase cycling tasks with their ULs. Variations in cycling velocity and interlimb phase errors were computed as measures of coordination. Linear regression was used to examine age-coordination effects. Given the sensorimotor processing for bilateral movements and gradual development of the corpus callosum, we hypothesized different relationships between age and coordination for bilateral and unilateral movements. Results showed UL coordination was significantly related to age, where coordination was better in older compared to younger children (p < 0.001); however, there were similar significant effects for unilateral movements. Differences in unilateral and bilateral coordination were not significantly explained by biological sex, although power to detect sex differences was low. We conclude that bilateral and unilateral UL coordination are age-dependent; each improves at similar rates through childhood and adolescence.

The power of multivariate approach in identifying EEG correlates of interlimb coupling

Interlimb coupling refers to the interaction between movements of one limb and movements of other limbs. Understanding mechanisms underlying this effect is important to real life because it reflects the level of interdependence between the limbs that plays a role in daily activities including tool use, cooking, or playing musical instruments. Interlimb coupling involves multiple brain regions working together, including coordination of neural activity in sensory and motor regions across the two hemispheres. Traditional neuroscience research took a univariate approach to identify neural features that correspond to behavioural coupling measures. Yet, this approach reduces the complexity of the neural activity during interlimb tasks to one value. In this brief research report, we argue that identifying neural correlates of interlimb coupling would benefit from a multivariate approach in which full patterns from multiple sources are used to predict behavioural coupling. We demonstrate the feasibility of this approach in an exploratory EEG study where participants (n = 10) completed 240 trials of a well-established drawing paradigm that involves interlimb coupling. Using artificial neural network (ANN), we show that multivariate representation of the EEG signal significantly captures the interlimb coupling during bimanual drawing whereas univariate analyses failed to identify such correlates. Our findings demonstrate that analysing distributed patterns of multiple EEG channels is more sensitive than single-value techniques in uncovering subtle differences between multiple neural signals. Using such techniques can improve identification of neural correlates of complex motor behaviours.

Antagonist Muscle Prefatigue Increases the Intracortical Communication between Contralateral Motor Cortices during Elbow Extension Contraction

To investigate the cortico-cortical coupling changes related to antagonist muscle prefatigue, we recorded EEG at FC3, C3, FC4, and C4 electrodes of twelve young male volunteers during a 30-second-long, nonfatiguing isometric elbow extension contraction with a target force level of 20% MVC before and after a sustained fatiguing elbow flexion contraction until task failure. EEG-EEG phase synchronization indices in alpha and beta frequency bands were calculated for the pre- and postfatigue elbow extension contractions. The phase synchronization index in the beta frequency band was found significantly increased between EEG of FC3-C3. The increased phase synchronization index may reflect an enhanced intracortical communication or integration of the signals between contralateral motor cortices with antagonist muscle prefatigue, which may be related to the central modulation so as to compensate for the antagonist muscle prefatigue-induced joint instability.

A possible correlation between performance IQ, visuomotor adaptation ability and mu suppression

BACKGROUND

Psychometric, anatomical and functional brain studies suggest that individuals differ in the way that they perceive and analyze information and strategically control and execute movements. Inter-individual differences are also observed in neural correlates of specific and general cognitive ability. As a result, some individuals perceive and adapt to environmental conditions and perform motor activities better than others. The aim of this study was to identify a common factor that predicts adaptation of a reaching movement to a visual perturbation and suppression of movement-related brain activity (mu rhythms).

RESULTS

Twenty-eight participants participated in two different experiments designed to evaluate visuomotor adaptation and mu suppression ability. Performance intelligence quotient (IQ) was assessed using the revised Wechsler Adult Intelligence Scale. Performance IQ predicted adaptation index of visuomotor performance (r=0.43, p=0.02) and suppression of mu rhythms (r=-0.59; p<0.001). Participants with high performance IQ were faster at adapting to a visuomotor perturbation and better at suppressing mu activity than participants with low performance IQ.

CONCLUSIONS

We found a possible link between performance IQ and mu suppression, and performance IQ and the initial rate of adaptation. Individuals with high performance IQ were better in suppressing mu rhythms and were quicker at associating motor command and required movement than individuals with low performance IQ.

Motor Training-Induced Neuroplasticity

The present lab-review presents and discusses our previous and current research into motor training-induced neuroplasticity by classifying our work on the basis of two broad aspects: (1) the applied study design (i.e., cross-sectional vs. longitudinal) and (2) the complexity of the motor task subjected to training (i.e., elementary finger movements vs. highly complex physical activity). Together with others we demonstrate that training-induced anatomic and functional changes are evident for a wide range of motor tasks and for several age cohorts. Finally, we discuss our findings from a lifespan perspective and embed them in the context of research investigating the beneficial effect of motor training-induced neuroplasticity on brain aging.

Biophysical modulations of functional connectivity

Resting-state low frequency oscillations have been detected in many functional magnetic resonance imaging (MRI) studies and appear to be synchronized between functionally related areas. Converging evidence from MRI and other imaging modalities suggest that this activity has an intrinsic neuronal origin. Multiple consistent networks have been found in large populations, and have been shown to be stable over time. Further, these patterns of functional connectivity have been shown to be altered in healthy controls under various physiological challenges. This review will present the biophysical characterization of functional connectivity, and examine the effects of physical state manipulations (such as anesthesia, fatigue, and aging) in healthy controls.

Neural changes induced by learning a challenging perceptual-motor task

We studied the neural changes accompanying the learning of a perceptual-motor task involving polyrhythmic bimanual force production. Motor learning was characterized by an increase in stability of performance. To assess after-effects in the corresponding neural network, magnetoencophalographic and electromyographic signals were recorded and analyzed in terms of (event-related) amplitude changes and synchronization patterns. The topology of the network was first identified using a beamformer analysis, which revealed differential effects of activation in cortical areas and cerebellar hemispheres. We found event-related (de-)synchronization of beta-activity in bilateral cortical motor areas and alpha-modulations in the cerebellum. The alpha-modulation increased after learning and, simultaneously, the bilateral M1 coupling increased around the movement frequency reflecting improved motor timing. Furthermore, the inter-hemispheric gamma-synchronization between primary motor areas decreased, which may reflect a reduced attentional demand after learning.

Bimanual passive movement: functional activation and inter-regional coupling

The aim of this study was to investigate intra-regional activation and inter-regional connectivity during passive movement. During fMRI, a mechanic device was used to move the subject's index and middle fingers. We assessed four movement conditions (unimanual left/right, bimanual symmetric/asymmetric), plus Rest. A conventional intra-regional analysis identified the passive stimulation network, including motor cortex, primary and secondary somatosensory cortex, plus the cerebellum. The posterior (sensory) part of the sensory-motor activation around the central sulcus showed a significant modulation according to the symmetry of the bimanual movement, with greater activation for asymmetric compared to symmetric movements. A second set of fMRI analyses assessed condition-dependent changes of coupling between sensory-motor regions around the superior central sulcus and the rest of the brain. These analyses showed a high inter-regional covariation within the entire network activated by passive movement. However, the specific experimental conditions modulated these patterns of connectivity. Highest coupling was observed during the Rest condition, and the coupling between homologous sensory-motor regions around the left and right central sulcus was higher in bimanual than unimanual conditions. These findings demonstrate that passive movement can affect the connectivity within the sensory-motor network. We conclude that implicit detection of asymmetry during bimanual movement relies on associative somatosensory region in post-central areas, and that passive stimulation reduces the functional connectivity within the passive movement network. Our findings open the possibility to combine passive movement and inter-regional connectivity as a tool to investigate the functionality of the sensory-motor system in patients with very poor mobility.

The functional significance of mu rhythms: translating "seeing" and "hearing" into "doing"

Existing evidence indicates that mu and other alpha-like rhythms are independent phenomena because of differences in source generation, sensitivity to sensory events, bilateral coherence, frequency, and power. Although mu suppression and enhancement echo sensorimotor processing in frontoparietal networks, they are also sensitive to cognitive and affective influences and likely reflect more than an idling brain state. Mu rhythms are present at early stages of human development and in other mammalian species. They exhibit adaptive and dynamically changing properties, including frequency acceleration and posterior-to-anterior shifts in focus. Furthermore, individuals can learn to control mu rhythms volitionally in a very short period of time. This raises questions about the mu rhythm's open neural architecture and ability to respond to cognitive, affective, and motor imagery, implying an even greater developmental and functional role than has previously been ascribed to it. Recent studies have suggested that mu rhythms reflect downstream modulation of motor cortex by prefrontal mirror neurons, i.e., cells that may play a critical role in imitation learning and the ability to understand the actions of others. It is proposed that mu rhythms represent an important information processing function that links perception and action-specifically, the transformation of "seeing" and "hearing" into "doing." In a broader context, this transformation function results from an entrainment/gating mechanism in which multiple alpha networks (visual-, auditory-, and somatosensory-centered domains), typically producing rhythmic oscillations in a locally independent manner, become coupled and entrained. A global or 'diffuse and distributed alpha system' comes into existence when these independent sources of alpha become coherently engaged in transforming perception to action.

Functional connectivity changes with concentration of sevoflurane anesthesia

Low-frequency oscillations (<0.08 Hz) have been detected in functional magnetic resonance imaging studies, and appear to be synchronized between functionally related areas. The effect of anesthetic agents on cortical activity is not completely characterized. This study assessed the effect of anesthesia on the temporal relations in activity in the motor cortices. Resting-state magnetic resonance data were acquired on six volunteers under different anesthetic states (using 0.0%, 2.0% and 1.0% stable end-tidal sevoflurane). Across all volunteers, the number of significant voxels (p<2.5 x 10) in the functional connectivity maps was reduced by 78% for light anesthesia and by 98% for deep anesthesia, compared with the awake state. Additionally, significant correlations in the connectivity maps were bilateral in the awake state but unilateral in the light anesthesia state.