Reaction Time Task Performance in Concussed Athletes over a 30-Day Period: An Observational Study.

OBJECTIVE: Reaction time is a common deficit following concussion, making its evaluation critical during return-to-play protocol. Without proper evaluation, an athlete may return-to-play prematurely, putting them at risk of further injury. Although often assessed, we propose that current clinical testing may not be challenging enough to detect lingering deficits. Thus, the aim of this study was to examine reaction time in concussed individuals three times over a 30-day period through the use of a novel reaction time device consisting of simple, complex, and go/no-go reaction time tasks. METHODS: Twenty-three concussed subjects completed simple, complex, and go/no-go reaction time tests at three different timepoints: within 7-, 14-, and 30-days of injury, and 21 healthy controls completed the three reaction time tasks during a single session. RESULTS: Independent t-tests revealed that for the simple reaction time task, concussed participants were only significantly slower at session 1 (p = .002) when compared to controls. Complex reaction time task results showed concussed participants to be significantly slower at session 1 (p = .0002), session 2 (p = .001), and session 3 (p = .002). Go/no-go results showed concussed participants to be significantly slower than controls at session 1 (p = .003), session 2 (p = .001), and session 3 (p = .001). CONCLUSIONS: Concussed individuals display prolonged reaction time deficits beyond the acute phase of injury, illustrated using increasingly complex tasks.

Residual alterations of brain electrical activity in clinically asymptomatic concussed individuals: an EEG study.

OBJECTIVE: To examine the neural substrates underlying performance on Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) and HeadRehab Virtual Reality (VR) balance and spatial modules in a concussed and control group. METHODS: Thirteen controls and seven concussed participants were fitted with a Geodesic 128-channel EEG cap and completed three assessments: EEG baseline, ImPACT testing, and VR balance and spatial modules. Concussed participants completed were tested within 8 (5 ± 1) days after injury. RESULTS: EEG power was significantly (p < .05) decreased in the concussed group over all testing modalities. EEG coherence was significantly (p < .05) increased in the concussed group during EEG baseline and ImPACT. For VR testing, two conditions showed significant (p < .05) increases in EEG coherence between ROIs, while two different conditions showed significant (p < .05) decreases in coherence levels. CONCLUSIONS: Concussed participants passed all clinical concussion testing tools, but showed pathophysiological dysfunction when evaluating EEG variables. SIGNIFICANCE: Concussed participants are able to compensate and achieve normal functioning due to recruiting additional brain networks. This allows concussed participants to pass clinical tests while still displaying electrophysiological deficits and clinicians must consider this information when making return-to-play decisions.

Alteration of brain functional network at rest and in response to YMCA physical stress test in concussed athletes: RsFMRI study.

There is still controversy in the literature whether a single episode of mild traumatic brain injury (mTBI) results in short- and/or long-term functional and structural deficits in the concussed brain. With the inability of traditional brain imaging techniques to properly assess the severity of brain damage induced by a concussive blow, there is hope that more advanced applications such as resting state functional magnetic resonance imaging (rsFMRI) will be more specific in accurately diagnosing mTBI. In this rsFMRI study, we examined 17 subjects 10±2 days post-sports-related mTBI and 17 age-matched normal volunteers (NVs) to investigate the possibility that the integrity of the resting state brain network is disrupted following a single concussive blow. We hypothesized that advanced brain imaging techniques may reveal subtle alterations of functional brain connections in asymptomatic mTBI subjects. There are several findings of interest. All mTBI subjects were asymptomatic based upon clinical evaluation and neuropsychological (NP) assessments prior to the MRI session. The mTBI subjects revealed a disrupted functional network both at rest and in response to the YMCA physical stress test. Specifically, interhemispheric connectivity was significantly reduced in the primary visual cortex, hippocampal and dorsolateral prefrontal cortex networks (p<0.05). The YMCA physical stress induced nonspecific and similar changes in brain network connectivity patterns in both the mTBI and NV groups. These major findings are discussed in relation to underlying mechanisms, clinical assessment of mTBI, and current debate regarding functional brain connectivity in a clinical population. Overall, our major findings clearly indicate that functional brain alterations in the acute phase of injury are overlooked when conventional clinical and neuropsychological examinations are used.

Practice-related modulations of force enslaving and cortical activity as revealed by EEG.

OBJECTIVE: To examine the role of practice in the modification of force enslaving and motor-related cortical potentials using finger force production tasks. This study follows-up previous studies in our laboratory using experienced piano players. METHODS: Two experiments were performed. In Expt. 1, 6 subjects participated in a pre and post EEG session separated by 12 practice sessions which were conducted 3 days a week for 4 weeks. With visual feedback regarding the accuracy of force output, subjects produced one of two force levels with either their ring or index finger. Experiment 2 followed a similar procedure to that of Expt. 1 with additional visual feedback to the degree of finger independency. Both behavioral (isometric force output) and EEG data preceding and accompanying force responses were measured. RESULTS: In Expt. 1 we found that forced enslaving increased along with improved accuracy following 4 weeks of practice. We found a reduction of motor potential (MP) amplitude for the index but not the ring finger following practice. Experiment 2 showed an increase in accuracy and reduction in force enslaving after practice with adequate feedback. The amplitude of MP for the index finger also decreased after practice as in Expt. 1. In contrast, the amplitude of MP for the ring finger increased after practice. CONCLUSIONS: The present study extends our earlier work with piano players and shows the role of practice in modifying behavioral and cortical measures. The concluding theme emergent from our studies is that individuated finger control is not hard-wired, but rather plastic and greatly influenced by deliberate practice. SIGNIFICANCE: This research supports the idea that experience and practice are associated with changes in behavioral and EEG correlates of task performance and have clinical implications in disorders such as stroke or dystonia. Practice-related procedures offer useful approaches to rehabilitation strategies.

Feedback-dependent modulation of isometric force control: an EEG study in visuomotor integration.

The primary purpose of this investigation was to examine the cortical mechanisms underlying visuomotor integration in an experiment directly manipulating visual feedback (control-signal gain) as participants executed a grasping task. This was accomplished by assessing human electroencephalograms in both time and frequency domains and relating these measures to the performance accuracy of isometric force control. The basic experimental manipulation consisted of subjects controlling a grip dynamometer and the subsequent force trace displayed on a computer monitor at various magnitudes of force output and control-signal gain. Several findings from this study were of interest. First, the effects of control-signal gain and its interplay with the magnitude of force were most evident across the parietal and frontocentral electrode locations--areas specifically related to multi-modal sensory evaluation (parietal lobe) and higher-order movement control (supplementary and mesial premotor areas). Second, electroencephalography (EEG) measures in the time domain, i.e., slow-wave potentials, were sensitive to control-signal gain only during the ramp phase of force production (period of reaching the target force), not the static phase (period of maintaining the target force level). Third, EEG measures within the frequency domain (event-related desynchronization), unlike the slow-wave potential measures, were sensitive to control-signal gain during the static phase of force production--a sensitivity that was directly related to improvements in the accuracy of isometric force control. The findings of this investigation are described in relation to the existent literature on human visuomotor integration with special attention paid to the distinct spatial and temporal electrocortical patterns exhibited under varying degrees of visual feedback and magnitudes of force output during grasping.

Movement-related potentials are task or end-effector dependent: evidence from a multifinger experiment.

In a number of recent studies, the specific sensitivity of movement-related EEG potentials toward experimental manipulations of motor tasks using the index finger as a primary end-effector is well documented. The major question in this study was whether different movement-related EEG components are primarily end-effector or task dependent. Accordingly, the experimental task (i.e., the rate of force development - a ratio of peak force to time-to-peak force) was systematically manipulated and the effects of this manipulation on movement-related potentials were examined while subjects used either the index, middle, ring or little finger. Significant effects observed in this study were due mainly to the sensitivity of movement-related potentials preceding movement onset (Bereit shafts potential and motor potential) toward the specific finger performing the task and the sensitivity of components accompanying the task (movement-monitoring potential) toward the rate of force development. In addition, both movement-related potentials preceding and accompanying movement significantly changed as a function of the finger performing the slow task (lower rate of force development) with maximum values observed for the ring finger and minimal values observed for the index finger. Behaviorally subjects were less accurate during slow tasks regardless of the finger performing the task. In contrast, the amplitude of neither early nor late components of movement-related potentials changed as a function of the finger performing the fast task (higher rate of force development). Overall, our results are consistent with the notion that the whole complex of movement-related EEG potentials reflect a combination of factors including the selection of corresponding general motor programs as reflected in the amplitude of potentials preceding movement and specific elements of the task including rate of force development as reflected in the amplitude of potentials accompanying movement execution.

Negative cortical d.c. shifts associated with coordination and control in a prehensile force task.

Movement-related cortical d.c. shifts accompanying the execution of four different prehensile tasks were investigated using six normal adult subjects. The goal was to identify patterns of brain electrical activity that differentiated a precision grip configuration (thumb and index finger or 2f) from a full precision grip configuration (thumb and all fingers or 5f) at different total force levels. As such, this was the first study to systematically manipulate both grip configuration and force level while also measuring movement-related potentials (MRP) during the control phase of an isometric prehensile task. This investigation focused on assessing the sustained, performance-related negativity (N-P) associated with the execution of particular grip configurations at different total force levels (percentage maximum voluntary force, MVF). The results from this study demonstrated significant interactions between grip configuration, force level and amplitude of the N-P. First, an overall increase in force output does not correspond to larger N-P amplitudes under these task conditions. Second, force level and grip configuration interact significantly in determining the peak N-P, especially in low-force conditions. Overall, the findings reveal a task-specific sensitivity of movement-related potentials associated with the control phase of a prehensile force task while humans execute different grip configurations and force levels.

Neurophysiological and behavioral indices of time pressure effects on visuomotor task performance.

Using a video game format, this study examined the effects of time pressure (TP) on behavioral and electrocortical indices. The behavioral results were consistent with previous time pressure research in that TP reduced time to perform a task and increases behavioral errors. In addition, electroencephalogram (EEG) measures showed distinctive patterns associated with TP in the theta, mu, and gamma bands along the midline. Site specific changes in the success vs. failure trials were also seen in midline theta at Fz, gamma at Fz, and mu at Cz. Right parietal alpha also differentiated TP and success vs. failure trials. In specific TP (1) increased frontal midline theta activity and (2) increased gamma at midline (frontal, central, and partietal) and in right frontal areas. The results of these findings are discussed in terms of the formation of specific neurocognitive strategies as evidenced by the topographic distribution of task-related modulation of the EEG within certain frequency bands. It is suggested that the effect of TP on visuomotor performance is mediated by adopting either task-relevant or task-irrelevant neurocognitive strategies as evidenced by successful or failed trials, respectively. Whether these strategies are formulated prior to performance or appear spontaneously during task performance remains unclear and is awaiting further experimentation.

Movement-related potentials with reference to isometric force output in discrete and repetitive tasks.

This study investigates whether different speed and accuracy constraints in discrete and repetitive index finger isometric force-production tasks influence the characteristics of the movement-related potentials (MRP) preceding and accompanying these tasks. Three components of MRP (Bereitschaftspotential, BP, motor potential, MP, and movement-monitoring potential, MMP) associated with isometric force output were identified and examined. Our principal finding for the MRP amplitude showed that only MMP, not BP and MP, was enhanced at higher rates of force development for both speed and accuracy tasks. That is to say, there was a high correlation between MMP peak amplitude and the rate of force development for both repetitive and discrete force-production tasks. Additionally, the amplitude of MMP was consistently higher for fast, rather than accurate, force outputs. Moreover, the results from analysis of MRP onset times suggest that, in general, the MRP begin earlier for the fast force output than for the accurate force output.

Movement-related potentials accompanying unilateral finger movements with special reference to rate of force development.

The aim of this study was to examine the relationship between force and rate of force development with electroencephalogram correlates. The primary question was whether the different components of movement related potentials (MRPs) were related to specific properties of force output while subjects performed index finger force production tasks. The peak force and rate of force development (e.g., a product of peak force over time-to-peak force) were manipulated, and the effects of these manipulations on components of MRPs preceding and accompanying force production tasks were examined. The hypothesis was that the rate of force development, rather than level of force itself, would directly influence the later component of MRPs. Consistent with this hypothesis was the finding that the amplitudes of MRP components preceding (MP) and accompanying (MMP, MTP) finger force production movements were significantly correlated with force development rate.

Aging and time to instability in posture.

Two experiments are reported that were set up to examine the spatial-temporal boundaries of postural instability in upright stance as a function of age (60-96 years) and postural conditions. Subjects stood on a force platform under different experimental conditions (vision/no vision and arms up/down) so that the effect of age on key dynamic properties of postural stability could be determined. The findings showed that the ratio of the area of the motion of the center of pressure to the area within the stability boundary increased with age. Also, the virtual time-to-contact with the postural stability boundary decreased with age. Collectively, the findings show that the margins to the spatial-temporal boundaries of postural stability decrease with advancing age in the elderly. These reduced margins of dynamic stability may be a factor contributing to the progressive instability of posture with aging in the elderly.

Stochastic processes in postural center-of-pressure profiles.

The stochastic processes of postural center-of-pressure profiles were examined in 3- and 5-year-old children, young adult students (mean 20 years), and an elderly age group (mean 67 years). Subjects stood still in an upright bipedal stance on a force platform under vision and nonvision conditions. The time evolutionary properties of the center-of-pressure dynamic were examined using basic stochastic process models. The amount of motion of the center of pressure decreased with increments of age from 3 to 5 years to young adult but increased again in the elderly age group. The availability of vision decreased the amount of motion of the center of pressure in all groups except the 3-year-old group, where there was less motion of the center of pressure with no vision. The stochastic properties of the center-of-pressure dynamic were assessed using both a two-process, random-walk model of Collins and De Luca and an Ornstein-Uhlenbeck model that is linear and has displacement governed only by a single stiffness term in the random walk. The two-process open- and closed-loop model accounted for about 96% and the Ornstein-Uhlenbeck model 92% of the variance of the diffusion term. Diffusion parameters in both models showed that the data were correlated and that they varied with age in a fashion consistent with developmental accounts of the changing regulation of the degrees of freedom in action. The findings suggest that it is premature to consider the trajectory of the center-of-pressure as a two-process, open- and closed-loop random-walk model given that: (a) the linear Ornstein-Uhlenbeck dynamic equation with only two parameters accommodates almost as much of the variance of the random walk; and (b) the linkage of a discontinuity in the diffusion process with the transition of open- to closed-loop processes is poorly founded. It appears that the nature of the stochastic properties of the random walk of the center-of-pressure trajectory in quiet, upright standing remains to be elucidated.

Virtual Time-to-Collision and Human Postural Control.

This article is a report on 3 experiments designed so that the role of virtual time-to-collision (VTC), which specifies the spatiotemporal proximity of the center of pressure to the postural stability boundary in the regulation of posture in upright stances, could be examined. Virtual time-to-collision was estimated for normal upright stance with different bases of support, and for postural oscillations in which the speed of movement and instructional constraints on the coordination mode used were manipulated. The results showed that virtual time-to-collision was predictably reduced as (a) the base of support was reduced, (b) the speed of the postural oscillation was increased, and (c) the number of biomechanical degrees of freedom regulated in the coordination mode increased. Over a range of task conditions, the coefficients of variation of the VTC time-series were significantly lower than the coefficients of variation for the velocity and acceleration time-series of the center of pressure. The absolute values of VTC increased with the increment of the ground reaction forces a performer generated to avoid falling while approaching the stability boundary. These findings are consistent with the proposition that VTC may serve as an organizing informational control parameter for posture.

Facial stereotypic movements and tardive dyskinesia in a mentally retarded population.

The facial stereotypies of adults diagnosed as having mental retardation and tardive dyskinesia were examined through a kinematic analysis of video-taped lip and tongue motions. A control group of healthy adult subjects without mental retardation was also examined in the production of preferred rates of lip and tongue oscillatory motions to provide a basis to assess the degree of movement variability in the stereotypies. The inter- and intraindividual variability of the movement form characteristics of the lip and tongue stereotypic motions was higher in the subjects with mental retardation. Results suggest that the low variability of discrete properties of movement kinematics may not be a defining feature of stereotypies. The concept of invariance in stereotypies may relate only to the topological kinematic properties of the movement sequence that provide the basis to infer that the same stereotypic movement sequence was reproduced from observation to observation.