Shaun G. Boe

Perturbation-evoked cortical activity reflects both the context and consequence of postural instability

The cerebral cortex may play a role in the control of compensatory balance reactions by optimizing these responses to suit the task conditions and/or to stimulus (i.e. perturbation) characteristics. These possible contributions appear to be reflected by pre-perturbation and post-perturbation cortical activity. While studies have explored the characteristics and possible meaning of these different events (pre- vs. post-) there is little insight into the possible association between them. The purpose of this study was to explore whether pre- and post-perturbation cortical events are associated or whether they reflect different control processes linked to the control of balance. Twelve participants were presented temporally-predictable postural perturbations under four test conditions. The Block/Random tasks were designed to assess modifiability in CNS gain prior to instability, while the Unconstrained/Constrained tasks assessed responsiveness to the magnitude of instability. Perturbations were evoked by releasing a cable which held the participant in a forward lean position. The magnitude of pre-perturbation cortical activity scaled to perturbation amplitude when the magnitude of the perturbation was predictable [F(3,11)=2.906, P<0.05]. The amplitude of pre-perturbation cortical activity was large when the size of the forthcoming perturbation was unknown (13.8 + or - 7.9, 11.4 + or - 9.9, 16.9 + or - 9.3, and 16.1 + or - 10.6 muV for the Block Unconstrained and Constrained and Random Unconstrained and Constrained, respectively). In addition, N1 amplitude scaled to perturbation amplitude regardless of whether the size of the forthcoming perturbation was known (30.1 + or - 17.7, 11.4 + or - 7.1, 30.9 + or - 18.4, 12.4 + or - 6.1 muV). This is the first work to examine modifiability in the pre-perturbation cortical activity related to postural set alterations. The cerebral cortex differentially processes independent components prior to and following postural instability to generate compensatory responses linked to the conditions under which instability is experienced.

Laterality of brain activity during motor imagery is modulated by the provision of source level neurofeedback.

Motor imagery (MI) may be effective as an adjunct to physical practice for motor skill acquisition. For example, MI is emerging as an effective treatment in stroke neurorehabilitation. As in physical practice, the repetitive activation of neural pathways during MI can drive short- and long-term brain changes that underlie functional recovery. However, the lack of feedback about MI performance may be a factor limiting its effectiveness. The provision of feedback about MI-related brain activity may overcome this limitation by providing the opportunity for individuals to monitor their own performance of this endogenous process. We completed a controlled study to isolate neurofeedback as the factor driving changes in MI-related brain activity across repeated sessions. Eighteen healthy participants took part in 3 sessions comprised of both actual and imagined performance of a button press task. During MI, participants in the neurofeedback group received source level feedback based on activity from the left and right sensorimotor cortex obtained using magnetoencephalography. Participants in the control group received no neurofeedback. MI-related brain activity increased in the sensorimotor cortex contralateral to the imagined movement across sessions in the neurofeedback group, but not in controls. Task performance improved across sessions but did not differ between groups. Our results indicate that the provision of neurofeedback during MI allows healthy individuals to modulate regional brain activity. This finding has the potential to improve the effectiveness of MI as a tool in neurorehabilitation.

Motor imagery-based brain activity parallels that of motor execution: Evidence from magnetic source imaging of cortical oscillations

Motor imagery (MI) is a form of practice in which an individual mentally performs a motor task. Previous research suggests that skill acquisition via MI is facilitated by repetitive activation of brain regions in the sensorimotor network similar to that of motor execution, however this evidence is conflicting. Further, many studies do not control for overt muscle activity and thus the activation patterns reported for MI may be driven in part by actual movement. The purpose of the current research is to further establish MI as a secondary modality of skill acquisition by providing electrophysiological evidence of an overlap between brain areas recruited for motor execution and imagery. Non-disabled participants (N=18; 24.7±3.8 years) performed both execution and imagery of a unilateral sequence button-press task. Magnetoencephalography (MEG) was utilized to capture neural activity, while electromyography used to rigorously monitor muscle activity. Event-related synchronization/desynchronization (ERS/ERD) analysis was conducted in the beta frequency band (15-30 Hz). Whole head dual-state beamformer analysis was applied to MEG data and 3D t-tests were conducted after Talairach normalization. Source-level analysis showed that MI has similar patterns of spatial activity as ME, including activation of contralateral primary motor and somatosensory cortices. However, this activation is significantly less intense during MI (p<0.05). As well, activation during ME was more lateralized (i.e., within the contralateral hemisphere). These results confirm that ME and MI have similar spatial activation patterns. Thus, the current research provides direct electrophysiological evidence to further establish MI as a secondary form of skill acquisition.

Mild Traumatic Brain Injury (mTBI) and chronic cognitive impairment: A scoping review

Mild traumatic brain injury (mTBI), or concussion, is the most common type of traumatic brain injury. With mTBI comes symptoms that include headaches, fatigue, depression, anxiety and irritability, as well as impaired cognitive function. Symptom resolution is thought to occur within 3 months post-injury, with the exception of a small percentage of individuals who are said to experience persistent post-concussion syndrome. The number of individuals who experience persistent symptoms appears to be low despite clear evidence of longer-term pathophysiological changes resulting from mTBI. In light of the incongruency between these longer-term changes in brain pathology and the number of individuals with longer-term mTBI-related symptoms, particularly impaired cognitive function, we performed a scoping review of the literature that behaviourally assessed short- and long-term cognitive function in individuals with a single mTBI, with the goal of identifying the impact of a single concussion on cognitive function in the chronic stage post-injury. CINAHL, Embase, and Medline/Ovid were searched July 2015 for studies related to concussion and cognitive impairment. Data relating to the presence/absence of cognitive impairment were extracted from 45 studies meeting our inclusion criteria. Results indicate that, in contrast to the prevailing view that most symptoms of concussion are resolved within 3 months post-injury, approximately half of individuals with a single mTBI demonstrate long-term cognitive impairment. Study limitations notwithstanding, these findings highlight the need to carefully examine the long-term implications of a single mTBI.

Specific Brain Lesions Impair Explicit Motor Imagery Ability: A Systematic Review of the Evidence

OBJECTIVE To determine which neurologic disorders/lesions impair or restrict motor imagery (MI) ability. DATA SOURCES CINAHL, Cochrane, Embase, MEDLINE, Web of Science, PsychINFO, Physiotherapy Evidence Database, and Grey Literature were searched between May 8 and May 14, 2014. Keywords and Medical Subject Headings from 2 concepts (MI and lesion) were exploded to include related search terms (eg, mental practice/mental imagery, neurologic damage/lesion). STUDY SELECTION Two independent reviewers assessed the 3861 studies that resulted from the database search. The studies were assessed for relevancy using the following inclusion criteria: use of explicit kinesthetic MI; neurologic lesion location identified; and use of an MI ability assessment tool. DATA EXTRACTION Twenty-three studies encompassing 196 participants were included. The 23 studies used 8 different methods for assessing MI ability. MI assessment scores were then normalized to facilitate comparison across studies. DATA SYNTHESIS Lesion locations comprised many brain areas, including cortical (eg, parietal and frontal lobes), subcortical (eg, basal ganglia, thalamus), and cerebellum. Lesion etiology primarily was comprised of stroke and Parkinson disease. Several participants presented with lesions resulting from other pathologies. Subjects with parietal lobe damage were most impaired on their ability to perform MI. Subjects with frontal lobe and basal ganglia damage also consistently showed impairment in MI ability. CONCLUSIONS Subjects with damage to specific brain structures, including the parietal and frontal lobes, showed impaired MI ability. As such, MI-based neurorehabilitation may not be efficacious in all patient populations. Therefore, decisions related to the use of MI in neurorehabilitation should, in part, be based on the patients underlying pathophysiology.

State-Related Changes in MEG Functional Connectivity Reveal the Task-Positive Sensorimotor Network

Functional connectivity measures applied to magnetoencephalography (MEG) data have the capacity to elucidate neuronal networks. However, the task-related modulation of these measures is essential to identifying the functional relevance of the identified network. In this study, we provide evidence for the efficacy of measuring “state-related” (i.e., task vs. rest) changes in MEG functional connectivity for revealing a sensorimotor network. We investigate changes in functional connectivity, measured as cortico-cortical coherence (CCC), between rest blocks and the performance of a visually directed motor task in a healthy cohort. Task-positive changes in CCC were interpreted in the context of any concomitant modulations in spectral power. Task-related increases in whole-head CCC relative to the resting state were identified between areas established as part of the sensorimotor network as well as frontal eye fields and prefrontal cortices, predominantly in the beta and gamma frequency bands. This study provides evidence for the use of MEG to identify task-specific functionally connected sensorimotor networks in a non-invasive, patient friendly manner.

Modified constraint-induced movement therapy for upper extremity recovery post stroke: what is the evidence?

Abstract Background: Constraint-induced movement therapy (CIMT) is an effective treatment for upper extremity (UE) recovery post stroke. Difficulties implementing a traditional CIMT approach have led to development of protocols featuring varying practice schedules, including a 10-week, 3 times per week intervention, termed modified CIMT (mCIMT). To date, systematic reviews of CIMT have grouped the various protocols, precluding the ability to ascertain the level of evidence (LOE) of specific CIMT protocols. Knowing the LOE for various protocols and their relative effectiveness may facilitate decision making regarding which protocol to implement. Objective: The aim of this study was to determine the LOE of mCIMT in promoting UE recovery post stroke. Methods: A comprehensive literature search and subsequent analysis identified studies of a range of designs that investigated the mCIMT protocol. Two independent reviewers assigned an LOE to each of the identified studies, which were then examined collectively to determine the overall LOE for mCIMT. Study results were reviewed to assess the effectiveness of mCIMT for improving UE recovery. Results: Of 473 studies identified, 15 utilized mCIMT. The lack of randomized controlled trials (RCT) resulted in assigning an intermediate LOE (C). Study results indicated that participants receiving mCIMT experienced clinically significant improvements in UE impairment and activity-level attributes. Conclusion: The mCIMT protocol is an effective intervention for UE recovery post stroke. Future research including large RCTs could potentially increase the LOE for mCIMT. Additional investigation into the effectiveness of mCIMT in acute and subacute stroke populations is warranted given the limited number of studies performed to date.

Characterizing skill acquisition through motor imagery with no prior physical practice.

Motor learning depends upon plasticity in neural networks involved in the planning and execution of movement. Physical practice (PP) is the primary means of motor learning, but it can be augmented with nonphysical forms of practice including motor imagery (MI)-the mental rehearsal of movement. It is unknown if MI alone, without prior PP of a movement, can produce robust learning. Here the authors used an implicit sequence learning task to explore motor learning via MI alone or PP. Participants underwent implicit sequence learning training via MI (n = 31) or PP (n = 33). Posttraining reaction time was faster for implicit versus random sequences for both the MI group (M = 583 ± 84 ms; 632 ± 86 ms, d = 0.59) and PP group (M = 532 ± 73 ms; 589 ± 70 ms, d = 0.80), demonstrating that MI without PP facilitated skill acquisition. Relative to MI alone, PP led to reduced reaction time for both random (d = 0.65) and implicit sequences (d = 0.55) consistent with a nonspecific motor benefit favoring PP over MI. These results have broad implication for theories of MI and support the use of MI as a form of practice to acquire implicit motor skills. (PsycINFO Database Record

High inter-rater reliability in analyzing results of decomposition-based quantitative electromyography in subjects with or without neuromuscular disorder

Decomposition-based quantitative electromyography (DQEMG) comprises a group of methods used to obtain information related to the health of the neuromuscular system. Although primarily objective, aspects of the data analysis protocol include operator decisions that may impact its reliability and reduce the applicability of the technique among multiple users. Thus, the objective of this study was to establish the inter-rater reliability of the protocol used for DQEMG analysis among five raters. Seventy data files previously obtained using DQEMG from healthy control subjects and patients with disorders of the neuromuscular system were analyzed by four novice and one experienced rater. Values obtained from this analysis were then evaluated for reliability within the novice raters and in contrast to the results of the experienced rater to examine the influence of the level of rater experience on the results obtained. The majority of the parameters associated with the number of motor unit potentials and their physiological characteristics were found to be reliable among all raters, with moderate-high ICC values observed for both the biceps brachii and first dorsal interosseous muscles. The data suggest that the level of rater experience does not greatly influence the results obtained and that the analysis can be reliably performed by a rater who is given suitable instruction. These findings are important particularly given the potential use of DQEMG as an outcome measure in multi-center studies.

Skill acquisition via motor imagery relies on both motor and perceptual learning.

Motor imagery (MI), the mental rehearsal of movement, is an effective means for acquiring a novel skill, even in the absence of physical practice (PP). The nature of this learning, be it perceptual, motor, or both, is not well understood. Understanding the mechanisms underlying MI-based skill acquisition has implications for its use in numerous disciplines, including informing best practices regarding its use. Here we used an implicit sequence learning (ISL) task to probe whether MI-based skill acquisition can be attributed to perceptual or motor learning. Participants (n = 60) randomized to 4 groups were trained through MI or PP, and were then tested in either perceptual (altering the sensory cue) or motor (switching the hand) transfer conditions. Control participants (n = 42) that did not perform a transfer condition were utilized from previous work. Learning was quantified through effect sizes for reaction time (RT) differences between implicit and random sequences. Generally, PP-based training led to lower RTs compared with MI-based training for implicit and random sequences. All groups demonstrated learning (p < .05), the magnitude of which was reduced by transfer conditions relative to controls. For MI-based training perceptual transfer disrupted performance more than for PP. Motor transfer disrupted performance equally for MI- and PP-based training. Our results suggest that MI-based training relies on both perceptual and motor learning, while PP-based training relies more on motor processes. These results reveal details regarding the mechanisms underlying MI, and inform its use as a modality for skill acquisition. (PsycINFO Database Record