Paul van Donkelaar

Preprogramming vs. on-line control in simple movement sequences

In the present experiment the acceleration traces produced during a repetitive arm extension/flexion movement were measured in addition to the RT required to initiate such a movement. The speed at which this task was completed as well as the number of extension/flexion segments were varied to allow for either preprogramming or on-line control. Evidence from the acceleration traces and the RT data suggested that the movements completed as quickly as possible were preprogrammed; whereas, those completed more slowly were controlled on-line. Furthermore, the topologies of the power spectral density functions from the acceleration traces of each type of movement displayed characteristics typical of these forms of control.

The potential for animal models to provide insight into mild traumatic brain injury: Translational challenges and strategies.

HighlightsMild traumatic brain injuries (mTBI) are common and in need of scientific research.There are confounding variables and limitations in mTBI patient studies.The use of animal models of may complement mTBI patient studies.Strengths/limitations of each model should be considered in study design and interpretation.Combined patient and animal model approach may allow for evidence‐based translation to clinical management. ABSTRACT Mild traumatic brain injury (mTBI) is a common health problem. There is tremendous variability and heterogeneity in human mTBI, including mechanisms of injury, biomechanical forces, injury severity, spatial and temporal pathophysiology, genetic factors, pre‐injury vulnerability and resilience factors, and clinical outcomes. Animal models greatly reduce this variability and heterogeneity, and provide a means to study mTBI in a rigorous, controlled, and efficient manner. Rodent models, in particular, are time‐ and cost‐efficient, and they allow researchers to measure morphological, cellular, molecular, and behavioral variables in a single study. However, inter‐species differences in anatomy, morphology, metabolism, neurobiology, and lifespan create translational challenges. Although the term “mild” TBI is used often in the pre‐clinical literature, clearly defined criteria for mild, moderate, and severe TBI in animal models have not been agreed upon. In this review, we introduce current issues facing the mTBI field, summarize the available research methodologies and previous studies in mTBI animal models, and discuss how a translational research approach may be useful in advancing our understanding and management of mTBI.

Myelin Water Fraction Is Transiently Reduced after a Single Mild Traumatic Brain Injury – A Prospective Cohort Study in Collegiate Hockey Players

Impact-related mild traumatic brain injuries (mTBI) are a major public health concern, and remain as one of the most poorly understood injuries in the field of neuroscience. Currently, the diagnosis and management of such injuries are based largely on patient-reported symptoms. An improved understanding of the underlying pathophysiology of mTBI is urgently needed in order to develop better diagnostic and management protocols. Specifically, dynamic post-injury changes to the myelin sheath in the human brain have not been examined, despite ‘compromised white matter integrity’ often being described as a consequence of mTBI. In this preliminary cohort study, myelin water imaging was used to prospectively evaluate changes in myelin water fraction, derived from the T2 decay signal, in two varsity hockey teams (45 players) over one season of athletic competition. 11 players sustained a concussion during competition, and were scanned at 72 hours, 2 weeks, and 2 months post-injury. Results demonstrated a reduction in myelin water fraction at 2 weeks post-injury in several brain areas relative to preseason scans, including the splenium of the corpus callosum, right posterior thalamic radiation, left superior corona radiata, left superior longitudinal fasciculus, and left posterior limb of the internal capsule. Myelin water fraction recovered to pre-season values by 2 months post-injury. These results may indicate transient myelin disruption following a single mTBI, with subsequent remyelination of affected neurons. Myelin disruption was not apparent in the athletes who did not experience a concussion, despite exposure to repetitive subconcussive trauma over a season of collegiate hockey. These findings may help to explain many of the metabolic and neurological deficits observed clinically following mTBI.

Cerebrovascular reactivity assessed by transcranial Doppler ultrasound in sport-related concussion: a systematic review

Background Traumatic brain injury influences regulation of cerebral blood flow in animal models and in human studies. We reviewed the use of transcranial Doppler ultrasound (US) to monitor cerebrovascular reactivity following sport-related concussion. Review method A narrative and systematic review of articles published in the English language, from December 1982 to October 2013. Data sources Articles were retrieved via numerous databases using relevant key terms. Observational, cohort, correlational, cross-sectional and longitudinal studies were included. Results Three publications met the criteria for inclusion; these provided data from 42 athletes and 33 controls. All three studies reported reductions in cerebrovascular reactivity via transcranial Doppler US. Conclusions These initial results support the use of cerebrovascular reactivity as a research tool for identifying altered neurophysiology and monitoring recovery in adult athletes. Larger cross-sectional, prospective and longitudinal studies are required to understand the sensitivity and prognostic value of cerebrovascular reactivity in sport-related concussion.

The effects of demanding temporal accuracy on the programming of simple tapping sequences

Abstract This experiment was undertaken in order to determine the effects of movement complexity and the demand for temporal accuracy on simple reaction time (SRT). Subjects listened to 2 to 5 tones separated by intertone intervals of 400 msec and attempted to initiate as quickly as possible, after an imperative stimulus, an accurate temporal reproduction of these tones by tapping on a single response key. Half of the subjects were allowed to vary from the 400 msec criterion without penalty (lenient temporal demands); and half were required to be within ±10% of the 400 msec criterion (360–440 msec) (stringent temporal demands). Increasing the number of taps within a sequence had no effect on SRT when the demands for temporal accuracy were lenient; but caused a nonlinear increase in SRT when stringent temporal demands were imposed. The results indicate that the additional requirement of accuracy had an effect on the manner in which the subjects prepared and initiated their responses. A rule-based approach is suggested as a possible explanation for the differences which occured.

Tactile gating in a reaching and grasping task

A multitude of events bombard our sensory systems at every moment of our lives. Thus, it is important for the sensory cortex to gate unimportant events. Tactile suppression is a well‐known phenomenon defined as a reduced ability to detect tactile events on the skin before and during movement. Previous experiments found detection rates decrease just prior to and during finger abduction, and decrease according to the proximity of the moving effector. This study examined how tactile detection changes during a reach to grasp. Fourteen human participants used their right hand to reach and grasp a cylinder. Tactors were attached to the index finger, the fifth digit, and the forearm of both the right and left arm and vibrated at various epochs relative to a “go” tone. Results showed that detection rates at the forearm decreased before movement onset; whereas at the right index finger, right fifth digit and at the left index finger, left fifth digit, and forearm sites did not decrease like in the right forearm. These results indicate that the task affects gating dynamics in a temporally‐ and contextually dependent manner and implies that feed‐forward motor planning processes can modify sensory signals.

Distracting visuospatial attention while approaching an obstacle reduces the toe‑obstacle clearance

Obstacle crossing during walking requires visuospatial attention to identify the obstacle, so that individuals can integrate visual and somatosensory information for raising the foot with appropriate height and timing without being tripped. However, the interaction between control of foot trajectory and orientation of visuospatial attention during obstacle crossing is complicated and remains unclear. This study probed where attention is directed when approaching and stepping over an obstacle during gait and examined how the presence of the obstacle affects the distribution of attention during walking. Eleven young healthy adults performed a visuospatial attention task while standing (Stand), crossing over an obstacle placed either before (ObsBefore) or after (ObsAfter) the visual target, or crossing without the visual target (ObsOnly). Toe-obstacle clearance was reduced for the trailing leg in the ObsAfter condition but remained the same for the ObsBefore and ObsOnly conditions. In addition, the accuracy rate of the visuospatial attention task tended to be higher at the locations closer to the obstacle. Taken together, these results demonstrate that visuospatial attention and the processes underlying obstacle crossing during locomotion interact in both a spatially and temporally dependent manner.

Executive Dysfunction Assessed with a Task-Switching Task following Concussion

Concussion frequently results in executive function deficits that can be specifically probed using task-switching tasks. The current study examined in detail the influence of concussion on task switching performance using both spatial and numerical stimuli. Individuals with concussion (nu200a=u200a16) were tested within 48 hours of injury and 7, 14, and 28 days later. Healthy sex-, age-, height-, weight- and activity-matched controls (nu200a=u200a16) were also tested at the same intervals. Switch costs were significantly greater in the participants with concussion than in the controls for both types of stimuli. By contrast, the global costs on non-switching trials were unaffected by concussion. We conclude that concussion has pronounced negative effects on the ability to switch task sets that generalize across task combinations (spatial or numerical) and that persist across at least a month after injury.

Explicit knowledge and real-time action control: anticipating a change does not make us respond more quickly

When the target of a goal-directed reach changes location, people normally respond rapidly and automatically to the target shift. Here, we investigate whether explicit knowledge about a moving target (knowing whether a location change is likely/unlikely) improves responsiveness, with the goal of understanding top-down effects on real-time reaching. In Experiment 1, we presented participants with pre-cues that indicated a 20 or 80xa0% likelihood of a target perturbation on that trial. When participants made pro-pointing responses to the target perturbations, their online response occurred later for 20xa0% trials than for 80xa0% trials, but this effect may have been due to suppression of the online response on 20xa0% trials, rather than enhancement of the response on 80xa0% trials. In Experiment 2, we presented participants with 50 and 100xa0% likelihood pre-cues, and observed no shortening of the latency on 100xa0% trials compared to 50xa0% trials, which suggests that expectation does not enhance the automatic response to a perturbation. However, we did observe more vigorous responses to the perturbation on the 100xa0% trials, and this contributed to shorter movement times relative to the 50xa0% trials. We also examined, in Experiment 2, whether prior knowledge about the direction of the target perturbation would shorten the latency of the online response, but we did not observe any reduction in latency. In sum, the onset of the automatic response appears to be suppressible, but not augmentable by top-down input. The possibility that the forcefulness of the automatic response is modifiable by expectation is examined, but not resolved.

Where's Waldo? The utility of a complicated visual search paradigm for transcranial Doppler-based assessments of neurovascular coupling.

BACKGROUNDnThe concept of neurovascular coupling has been postulated since the late 1800s and has been demonstrated most commonly in humans using visual stimuli (e.g. reading, checkerboards). These traditional paradigms evoke only a moderate cerebral blood flow response due to the relative simplicity of the visual stimuli.nnnNEW METHODnForty subjects completed three visual paradigms each challenging the visual processing areas to a different extent: reading text, complicated visual searching (new method: Wheres Waldo) and viewing coloured dots. Posterior and middle cerebral artery (PCA, MCA) velocities were recorded using transcranial Doppler ultrasound during each visual paradigm.nnnRESULTSnPrior to the presentation of the visual stimuli there were no differences in mean arterial pressure, or PCA or MCA velocities for the three paradigms. All three paradigms led to an elevation in PCA and MCA velocities after a delay (∼1.1s). Whereas velocity elevation was consistent across the three paradigms in the MCA, it was markedly larger during the Wheres Waldo task in the PCA. Thus, although the onset of the neurovascular coupling response was similar across the three visual paradigms, its overall magnitude was stimulus-dependent.nnnCOMPARISON WITH EXISTING METHODSnGiven that PCA velocity can be affected by blood pressure or carbon dioxide alterations, traditional neurovascular coupling paradigms (e.g. reading, checkerboards) appear to have a lower signal-to-noise ratio than that observed in complicated visual search tasks such as Wheres Waldo.nnnCONCLUSIONSnWe recommend complicated visual search paradigms such as Wheres Waldo be considered for future transcranial Doppler-based neurovascular coupling studies.