Lara A. Boyd

Explicit information interferes with implicit motor learning of both continuous and discrete movement tasks after stroke.

A large portion of the rehabilitation experience after stroke relies on implicit learning. However, our understanding of how best to facilitate motor learning after stroke is limited by a paucity of research that has explored the interaction between explicit information and implicit learning across various task domains. Previously we reported that the delivery of explicit instructions disrupted implicit motor learning after stroke that involved the sensorimotor cortical areas or basal ganglia. The purpose of this study was to determine the robustness of these findings by determining whether they could be replicated with 2 motor tasks, one discrete and one continuous, employed by the same group of participants. Then individuals with stroke in the sensorimotor cortical areas (SMC), 10 with stroke in the basal ganglia (BG), and 10 age-matched healthy controls (HC) participated in this study. Each completed 3 days of practice of both a discrete implicit motor task (the serial reaction time task) and a continuous motor task (the continuous tracking task); all returned on a fourth day for retention tests. By random designation, participants were divided into either the explicit information (EI) or no explicit information (No-EI) groups. Consistent with previous results, we found that the response to explicit information after stroke was uniformly negative regardless of task or lesion location; both stroke groups demonstrated an interference effect of explicit information while the healthy control group did not. Strengthening these findings is the fact that the interference effect of explicit information was not task dependent. This point is particularly important for rehabilitation scientists as they instruct clients during various therapeutic tasks after stroke. Our data suggest that certain forms of explicit information delivered before task practice may not be as useful for learning as discovering the solution to the motor task with practice alone, and this is regardless of the type of task being learned.

Implicit motor-sequence learning in humans following unilateral stroke: the impact of practice and explicit knowledge

Learning and memory are sub-served by two interrelated systems - explicit and implicit. Explicit memory involves facts, while one form of implicit memory involves perceptual-motor processes. The purpose of this series of experiments was to investigate the ability of individuals with stroke-related brain damage to demonstrate implicit motor-sequence learning and the relative impacts of (1) extended practice, or (2) explicit knowledge prior to practice. Implicit learning was severely impaired without explicit knowledge and even under conditions of extended practice. However, when explicit knowledge was provided prior to practice, participants with stroke demonstrated implicit motor-sequence learning. These data suggest that following unilateral stroke, providing explicit information about the task and sequence can attenuate implicit motor learning deficits.

Cerebellar stroke impairs temporal but not spatial accuracy during implicit motor learning.

Objective. Numerous studies have demonstrated cerebellar activity during implicit motor learning, but few have addressed its specific role. The purpose of this study was to determine if specific components (spatial or temporal) of an implicit motor-tracking task were affected by cerebellar stroke. Methods. The authors studied the performance of individuals with unilateral cerebellar stroke (n =7)and a control group (n = 10) across 3 acquisition days and at a delayed retention test as they practiced a unimanual tracking task with the contralesional upper extremity. Results. After cerebellar stroke, participants demonstrated reduced tracking errors for repeating sequences compared to random sequences; however, decomposition of tracking performance into temporal and spatial components revealed persistent deficits in tracking time lag despite improved spatial accuracy. A lesion analysis showed that the dentate nucleus was the only common region affected by all cerebellar strokes. Conclusions. During implicit motor learning, the cerebellum appears to participate in the formation of predictive strategies for the timing of motor responses, rather than for the accuracy of motor execution. Because deficits were found in the contralesional upper extremity, the authors suggest that this function is not lateralized to 1 hemisphere; cerebellar output may affect the formation of an internal model for timing movements in both upper extremities.

Implicit Sequence-Specific Motor Learning After Subcortical Stroke is Associated with Increased Prefrontal Brain Activations: An fMRI Study

Implicit motor learning is preserved after stroke, but how the brain compensates for damage to facilitate learning is unclear. We used a random effects analysis to determine how stroke alters patterns of brain activity during implicit sequence‐specific motor learning as compared to general improvements in motor control. Nine healthy participants and nine individuals with chronic, right focal subcortical stroke performed a continuous joystick‐based tracking task during an initial functional magnetic resonance images (fMRI) session, over 5 days of practice, and a retention test during a separate fMRI session. Sequence‐specific implicit motor learning was differentiated from general improvements in motor control by comparing tracking performance on a novel, repeated tracking sequence during early practice and again at the retention test. Both groups demonstrated implicit sequence‐specific motor learning at the retention test, yet substantial differences were apparent. At retention, healthy control participants demonstrated increased blood oxygenation level dependent (BOLD) response in left dorsal premotor cortex (PMd; BA 6) but decreased BOLD response left dorsolateral prefrontal cortex (DLPFC; BA 9) during repeated sequence tracking. In contrast, at retention individuals with stroke did not show this reduction in DLPFC during repeated tracking. Instead implicit sequence‐specific motor learning and general improvements in motor control were associated with increased BOLD response in the left middle frontal gyrus BA 8, regardless of sequence type after stroke. These data emphasize the potential importance of a prefrontal‐based attentional network for implicit motor learning after stroke. This study is the first to highlight the importance of the prefrontal cortex for implicit sequence‐specific motor learning after stroke. Hum Brain Mapp, 2011.

Motor learning after stroke: Is skill acquisition a prerequisite for contralesional neuroplastic change?

Limited data directly characterize the dynamic evolution of brain activity associated with motor learning after stroke. The current study considered whether sequence-specific motor skill learning or increasing non-specific use of the hemiparetic upper extremity drive functional reorganization of the contralesional motor cortex after stroke. Eighteen individuals with chronic middle cerebral artery stroke practiced one of two novel motor tasks; a retention test occurred on a separate fifth day. Using the hemiparetic arm, participants performed a serial targeting task during two functional MRI scans (day one and retention). Participants were randomized into either a task-specific group, who completed three additional sessions of serial targeting practice, or a general arm use group, who underwent three training sessions of increased but non-task specific use of the hemiparetic arm. Both groups performed a repeated sequence of responses that may be learned, and random sequences of movement, which cannot be learned. Change in reaction and movement time for the repeated sequence indexed motor learning; shifts in the laterality index (LI) within primary motor cortex (M1) for repeated and random sequences illustrated training effects on brain activity. Task-specific practice of the repeated sequence facilitated motor learning and shifted the LI for M1 as shown by a reduced volume of contralesional cortical activity. Random sequence performance did not stimulate motor learning or alter the LI within the task-specific training group. Further, between-group comparisons showed that increasing general arm use did not induce motor learning or alter brain activity for either random or repeated sequences. Motor skill learning of a repeated sequence altered cortical activation by inducing a more normal, contralateral pattern of brain activation. Our data suggest that task-specific motor learning may be an important stimulant for neuroplastic change and can remediate maladaptive patterns of brain activity after stroke.

Sleep to learn after stroke: Implicit and explicit off-line motor learning

After stroke, many individuals experience persistent motor impairments as well as altered patterns of sleep. Therefore, examining the role of sleep in motor skill learning following stroke is a critical issue. Other learning variables, such as type of instruction, may interact with sleep to influence sleep-dependent motor learning. Forty individuals with stroke and 40 control participants practiced a continuous motor tracking task and then either slept (sleep condition) or stayed awake (no-sleep condition) between practice and retention testing. Half were provided explicit information regarding the presence of a repeating sequence (explicit condition), while the other half were not (implicit condition). After stroke, individuals demonstrated sleep-dependent off-line motor learning of both the implicit and explicit version of the continuous tracking task; however, individuals with stroke who stayed awake between practice and retention testing did not demonstrate an improvement in motor performance at retention. Neither sleep nor instruction differentiated the performance of the healthy control participants. These data suggest that aspects of motor recovery after stroke may be modulated by sleep.

Is Health-Related Quality of Life Improving After Stroke?: A Comparison of Health Utilities Indices Among Canadians With Stroke Between 1996 and 2005

Background and Purpose— Recent innovations in diagnosis, management, and rehabilitation have resulted in measurable improvements in clinical and functional outcomes after acute stroke. However, whether gains in health-related quality of life after stroke have also occurred is not well characterized. Using 2 Canadian population surveys, the purpose of this study was to identify changes in health-related quality of life in individuals with stroke from 1996 to 2005. Methods— Data from the public use files of the National Population Health Survey, Cycle 2 (1996), and the Canadian Community Health Survey, Cycle 3.1. (2005), were used. A total of 847 individuals with stroke were included. Self-reported information on health status based on the Health Utilities Index Mark 3 was used to generate single-attribute and overall health-related quality of life scores. Analysis of covariance and multiple logistic regression were used to determine the relationship between survey year and poststroke impairment adjusting for demographic variables and clinical comorbidities. Results— A statistically significant and clinically important reduction in mean overall Health Utilities Index Mark 3 scores was observed for respondents with stroke from 1996 to 2005. In addition, 2 of the 8 single-attribute Health Utilities Index Mark 3 domains showed a significant change between survey years. Significantly more individuals with stroke reported dexterity and cognitive impairment in 2005 compared with respondents in 1996, indicating reduced health-related quality of life for these domains. Conclusion— Despite improvements in medical management, quality of life is not improving after stroke in the Canadian population. These findings are useful to generate hypotheses about the impact of advances in management on quality of life after stroke and identify specific domains that may benefit from future study in stroke populations.

Contralateral cerebellar damage impairs imperative planning but not updating of aimed arm movements in humans.

The specific motor control processes supported by the cerebellum and impaired with cerebellar damage remain unclear. The cerebellum has been implicated in both planning and updating of accurate movements. Previously, we used a statistical model to parcel aiming performance that was constrained by a timed-response paradigm into contributions attributed to a specified plan and feedforward updating. Here, we apply this procedure to determine the putative role of the cerebellum in planning and updating goal-directed aiming by comparing the performance of subjects with unilateral cerebellar stroke to controls. Subjects rapidly moved to targets in predictable or unpredictable conditions and cerebellar subjects used the contralesional limb to control for ipsilesional motor execution deficits. Displacement-derived movement velocity was used in the statistical model to determine the effect of planning and updating on accuracy. Compared to controls, the cerebellar group demonstrated errors in final position that were primarily determined by planning deficits. This finding is manifest in four ways: Cerebellar subjects (1) were less accurate than controls in both predictable and unpredictable conditions; (2) they showed minimal benefit from increased preparation time for target amplitude specification; (3) with ample time to plan direction, wrong direction response frequency was greater; and (4) final position was minimally determined by the plan. Because these deficits were found contralesional to the moving limb, the cerebellum’s role in planning is not lateralized to one hemisphere but rather our findings suggest that cerebellar output affects motor planning for both upper limbs. Indeed, a lesion analysis showed that the dentate nucleus, an area implicated in planning motor strategies and the primary cerebellar output nucleus, was the only common region affected by our patient group with contralateral cerebellar strokes.

Manipulating time-to-plan alters patterns of brain activation during the Fitts’ task

Fitts’ law predicts that there is an essential trade-off between speed and accuracy during movement. Past investigations of Fitts’ law have not characterized whether advance planning of upcoming fast and accurate movements impacts either behavior or patterns of brain activation. With an event-related functional magnetic resonance imaging (fMRI) paradigm, we investigated the neural correlates of advance planning and movement difficulty of rapid, goal-directed aimed movements using a discrete version of the classic Fitts’ task. Our behavioral data revealed strong differences in response time, initial movement velocity, and end-point accuracy based on manipulation of both time to plan movements and response difficulty. We discovered a modulation of the neural network associated with executing the Fitts’ task that was dependent on the availability of time to plan the upcoming movement and motor difficulty. Specifically, when time to plan for the upcoming movement was available, medial frontal gyrus (BA 10), pre-SMA (BA 6), putamen and cerebellar lobule VI were uniquely active to plan movements. Further, their activation correlated with behavioral measures of movement. In contrast, manipulating movement difficulty invoked a different pattern of brain activations in regions that are known to participate in motor control, including supplementary motor area (BA 6), sensory motor cortex (BA 4, 3, 2) and putamen. Our finding that medial frontal gyrus (BA 10) was important for discrete, fast and accurate movements expands the known role of this brain region, which in the past has been identified as a cognitive processing system supporting stimulus-oriented attending. We now extend this conceptualization to include motor functions such as those employed for processing for rapid, goal-directed aimed movements.

Motor sequence learning occurs despite disrupted visual and proprioceptive feedback

BackgroundRecent work has demonstrated the importance of proprioception for the development of internal representations of the forces encountered during a task. Evidence also exists for a significant role for proprioception in the execution of sequential movements. However, little work has explored the role of proprioceptive sensation during the learning of continuous movement sequences. Here, we report that the repeated segment of a continuous tracking task can be learned despite peripherally altered arm proprioception and severely restricted visual feedback regarding motor output.MethodsHealthy adults practiced a continuous tracking task over 2 days. Half of the participants experienced vibration that altered proprioception of shoulder flexion/extension of the active tracking arm (experimental condition) and half experienced vibration of the passive resting arm (control condition). Visual feedback was restricted for all participants. Retention testing was conducted on a separate day to assess motor learning.ResultsRegardless of vibration condition, participants learned the repeated segment demonstrated by significant improvements in accuracy for tracking repeated as compared to random continuous movement sequences.ConclusionThese results suggest that with practice, participants were able to use residual afferent information to overcome initial interference of tracking ability related to altered proprioception and restricted visual feedback to learn a continuous motor sequence. Motor learning occurred despite an initial interference of tracking noted during acquisition practice.