Cerebral peak alpha frequency predicts individual differences in pain sensitivity.

The identification of neurobiological markers that predict individual predisposition to pain are not only important for development of effective pain treatments, but would also yield a more complete understanding of how pain is implemented in the brain. In the current study using electroencephalography (EEG), we investigated the relationship between the peak frequency of alpha activity over sensorimotor cortex and pain intensity during capsaicin-heat pain (C-HP), a prolonged pain model known to induce spinal central sensitization in primates. We found that peak alpha frequency (PAF) recorded during a pain-free period preceding the induction of prolonged pain correlated with subsequent pain intensity reports: slower peak frequency at pain-free state was associated with higher pain during the prolonged pain condition. Moreover, the degree to which PAF decreased between pain-free and prolonged pain states was correlated with pain intensity. These two metrics were statistically uncorrelated and in combination were able to account for 50% of the variability in pain intensity. Altogether, our findings suggest that pain-free state PAF over relevant sensory systems could serve as a marker of individual predisposition to prolonged pain. Moreover, slowing of PAF in response to prolonged pain could represent an objective marker for subjective pain intensity. Our findings potentially lead the way for investigations in clinical populations in which alpha oscillations and the brain areas contributing to their generation are used in identifying and formulating treatment strategies for patients more likely to develop chronic pain.

Determining Levels of Upper Extremity Movement Impairment by Applying a Cluster Analysis to the Fugl-Meyer Assessment of the Upper Extremity in Chronic Stroke.

OBJECTIVE: To quantitatively determine levels of upper extremity movement impairment by using a cluster analysis of the Fugl-Meyer Assessment of the Upper Extremity (FMA-UE) with and without reflex items. DESIGN: Secondary analysis. SETTING: University and research centers. PARTICIPANTS: Individuals (N=247) with chronic stroke (>6mo poststroke). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Cutoff scores defined by FMA-UE total scores of clusters identified by 2 hierarchical cluster analyses performed on the full sample of FMA-UE individual item scores (with and without reflexes). Patterns of motor function defined by aggregate item scores of clusters. RESULTS: FMA-UE scores ranged from 2 to 63 (mean, 26.9±15.7) with reflex items and from 0 to 57 (mean, 22.1±15.3) without reflex items. Three clusters were identified. The distributions of the FMA-UE scores revealed considerable overlap between the clusters; therefore, 4 distinct stroke impairment levels were derived. CONCLUSIONS: For chronic stroke, the cluster analysis of the FMA-UE supports either a 3- or a 4-impairment level classification scheme.

Increased reward in ankle robotics training enhances motor control and cortical efficiency in stroke.

Robotics is rapidly emerging as a viable approach to enhance motor recovery after disabling stroke. Current principles of cognitive motor learning recognize a positive relationship between reward and motor learning. Yet no prior studies have established explicitly whether reward improves the rate or efficacy of robotics-assisted rehabilitation or produces neurophysiologic adaptations associated with motor learning. We conducted a 3 wk, 9-session clinical pilot with 10 people with chronic hemiparetic stroke, randomly assigned to train with an impedance-controlled ankle robot (anklebot) under either high reward (HR) or low reward conditions. The 1 h training sessions entailed playing a seated video game by moving the paretic ankle to hit moving onscreen targets with the anklebot only providing assistance as needed. Assessments included paretic ankle motor control, learning curves, electroencephalograpy (EEG) coherence and spectral power during unassisted trials, and gait function. While both groups exhibited changes in EEG, the HR group had faster learning curves (p = 0.05), smoother movements (p

Psychophysiological support of increasing attentional reserve during the development of a motor skill.

The aim of this study was to determine the relationship between motor skill and attentional reserve. Participants practiced a reaching task with the dominant upper extremity, to which a distortion of the visual feedback was applied, while a control group performed the same task without distortion. Event-related brain potentials (ERPs), elicited by auditory stimuli were recorded throughout practice. Performance, as measured by initial directional error, was initially worse relative to controls and improved over trials. Analyses of the ERPs revealed that exogenous components, N1 and P2, were undifferentiated between the groups and did not change with practice. Notably, amplitude of the novelty P3 component, an index of the involuntary orienting of attention, was initially attenuated relative to controls, but progressively increased in amplitude over trials in the learning group only. The results provide psychophysiological evidence that attentional reserve increases as a function of motor skill acquisition.

Stress, emotion regulation and cognitive performance: the predictive contributions of trait and state relative frontal EEG alpha asymmetry.

The relationship between trait and state measures of frontal lobe EEG alpha-band asymmetry in regard to indexing the approach-withdrawal dimension of emotion is unclear. The comparative predictive power of these constructs to explain emotion regulation and cognitive performance was examined under varying degrees of emotional challenge. The Capability Model posits the neural underpinnings of the relative difference in electrical activity between the left and right frontal lobes as a situational mechanism possibly indexing prefrontal-amygdalar interactions and psychological state. EEG, skin conductance, heart rate and acoustic startle amplitude were collected during a working memory task under three increasing levels of stress (final level was threat of shock). During threat of shock participants with higher state asymmetry exhibited greater emotion regulation compared to those with lower scores as indexed by significant attenuation of eyeblink startle magnitudes. The trait measure of frontal EEG asymmetry failed to account for significant variability in emotion regulation. Results implicate state-specific relative left frontal lobe activity as having an adaptive role in the regulation of emotion during cognitive challenge, but only under conditions of sufficient stress.

Clinical application of a modular ankle robot for stroke rehabilitation.

BACKGROUND: Advances in our understanding of neuroplasticity and motor learning post-stroke are now being leveraged with the use of robotics technology to enhance physical rehabilitation strategies. Major advances have been made with upper extremity robotics, which have been tested for efficacy in multi-site trials across the subacute and chronic phases of stroke. In contrast, use of lower extremity robotics to promote locomotor re-learning has been more recent and presents unique challenges by virtue of the complex multi-segmental mechanics of gait. OBJECTIVES: Here we review a programmatic effort to develop and apply the concept of joint-specific modular robotics to the paretic ankle as a means to improve underlying impairments in distal motor control that may have a significant impact on gait biomechanics and balance. METHODS: An impedance controlled ankle robot module (anklebot) is described as a platform to test the idea that a modular approach can be used to modify training and measure the time profile of treatment response. RESULTS: Pilot studies using seated visuomotor anklebot training with chronic patients are reviewed, along with results from initial efforts to evaluate the anklebot's utility as a clinical tool for assessing intrinsic ankle stiffness. The review includes a brief discussion of future directions for using the seated anklebot training in the earliest phases of sub-acute therapy, and to incorporate neurophysiological measures of cerebro-cortical activity as a means to reveal underlying mechanistic processes of motor learning and brain plasticity associated with robotic training. CONCLUSIONS: Finally we conclude with an initial control systems strategy for utilizing the anklebot as a gait training tool that includes integrating an Internal Model-based adaptive controller to both accommodate individual deficit severities and adapt to changes in patient performance.

The influence of social evaluation on cerebral cortical activity and motor performance: a study of "Real-Life" competition.

Motor performance in a social evaluative environment was examined in participants (N = 19) who completed a pistol shooting task under both performance-alone (PA) and competitive (C) conditions. Electroencephalographic (EEG), autonomic, and psychoendocrine activity were recorded in addition to kinematic measures of the aiming behavior. State anxiety, heart rate, and cortisol were modestly elevated during C and accompanied by relative desynchrony of high-alpha power, increased cortico-cortical communication between motor and non-motor regions, and degradation of the fluency of aiming trajectory, but maintenance of performance outcome (i.e., score). The findings reveal that performance in a complex social-evaluative environment characterized by competition results in elevated cortical activity beyond that essentially required for motor performance that translated as less efficient motor behavior.

Cerebral-cortical networking and activation increase as a function of cognitive-motor task difficulty.

Excessive increases in task difficulty typically result in marked attenuation of cognitive-motor performance. The psychomotor efficiency hypothesis suggests that poor performance is mediated by non-essential neural activity and cerebral cortical networking (inefficient cortical dynamics). This phenomenon may underlie the inverse relationship between excessive task difficulty and performance. However, investigation of the psychomotor efficiency hypothesis as it relates to task difficulty has not been conducted. The present study used electroencephalography (EEG) to examine cerebral cortical dynamics while participants were challenged with both Easy and Hard conditions during a cognitive-motor task (Tetris(®)). In accord with the psychomotor efficiency hypothesis, it was predicted that with increases in task difficulty, participants would demonstrate greater 'neural effort,' as indexed by EEG spectral power and cortical networking (i.e., EEG coherence) between the premotor (motor planning) region and sensory, executive, and motor regions. Increases in neural activation and cortical networking were observed during the Hard condition relative to the Easy condition, thus supporting the psychomotor efficiency hypothesis. To further determine the unique contributions of cognitive versus sensory-motor demands, a control experiment was conducted in which cognitive demand was increased while sensory-motor demand was held constant. This experiment revealed that regionally specific neural activation was influenced by changes in cognitive demand, whereas cortical networking to the motor planning region was sensitive only to changes in sensory-motor demand. Crucially, the present study is the first, to our knowledge, to characterize the separate impact of cognitive versus sensory-motor demands on cerebral cortical dynamics. The findings further inform the dynamics of the cortical processes that underlie the quality of cognitive-motor performance particularly with regard to task difficulty. A broader understanding of the brain and muscle interactions during varying levels of challenge may inform the design of effective training protocols aimed at optimizing cognitive-motor performance.

Cerebral cortical dynamics and the quality of motor behavior during social evaluative challenge.

To determine the influence of arousal on cerebral cortical dynamics and motor behavior, 58 channels of EEG were recorded in 13 college-age men (n=6) and women during an aiming task performed alone and in a social evaluation condition. Moderate arousal, as measured by heart rate, skin conductance, and self-reported mood, was induced during the social evaluation. In accord with the Yerkes-Dodson Hypothesis, which posits optimal performance during moderate arousal, improved performance (i.e., quality of the aiming trajectories) was observed. During social evaluation, changes in electroencephalogram dynamics included decreased coherence between the motor planning (Fz) and right temporal region (T4), increased coherence in the sensorimotor networks subserving the task, and increased local processing (gamma, 30-44 Hz) in the temporal regions. The results imply that moderate arousal promotes specific alterations in cortical dynamics that facilitate motor performance.