The subthalamic nucleus modulates the early phase of probabilistic classification learning.

Previous models proposed that the subthalamic nucleus (STN) is critical in the early phase of skill acquisition. We hypothesized that subthalamic deep brain stimulation modulates the learning curve in early classification learning. Thirteen idiopathic Parkinson's disease patients (iPD) with subthalamic deep brain stimulation (STN-DBS), 9 medically treated iPD, and 21 age-matched healthy controls were tested with a probabilistic classification task. STN-DBS patients were tested with stimulation OFF and ON, and medically treated patients with medication OFF and ON, respectively. Performance and reaction time were analyzed on the first 100 consecutive trials as early learning phase. Moreover, data were separated for low and high-probability patterns, and more differentiated strategy analyses were used. The major finding was a significant modulation of the learning curve in DBS patients with stimulation ON: although overall learning was similar to healthy controls, only the stimulation ON group showed a transient significant performance dip from trials '41-60' that rapidly recovered. Further analysis indicated that this might be paralleled by a modulation of the learning strategy, particularly on the high-probability patterns. The reaction time was unchanged during the dip. Our study supports that the STN serves as a relay in early classification learning and directs attention toward unacquainted content. The STN might play a role in balancing the short-term success against strategy optimization for improved long-term outcome.

Predictive value and reward in implicit classification learning.

Learning efficacy depends on its emotional context. The contents learned and the feedback received during training tinges this context. The objective here was to investigate the influence of content and feedback on the efficacy of implicit learning and to explore using functional imaging how these factors are processed in the brain. Twenty-one participants completed 150 trials of a probabilistic classification task (predicting sun or rain based on combinations of playing cards). Smileys or frowneys were presented as feedback. In 10 of these subjects, the task was performed during functional magnetic resonance imaging. Card combinations predicting sun were remembered better than those predicting rain. Similarly, positive feedback fortified learning more than negative feedback. The presentation of smileys recruited bilateral nucleus accumbens, sensorimotor cortex, and posterior cingulum more than negative feedback did. The higher the predictive value of a card combination, the more activation was found in the lateral cerebellum. Both context and feedback influence implicit classification learning. Similar to motor skill acquisition, positive feedback during classification learning is processed in part within the sensorimotor cortex, potentially reflecting the activation of a dopaminergic projection to motor cortex (Hosp et al., 2011). Activation of the lateral cerebellum during learning of combinations with high predictive value may reflect the formation of an internal model.

Chronic stroke survivors benefit from high-intensity aerobic treadmill exercise: a randomized control trial.

BACKGROUND AND OBJECTIVE: Ambulatory subjects after stroke may benefit from gait-oriented cardiovascular fitness training, but trials to date have not primarily assessed older persons. METHODS: Thirty-eight subjects (age >60 years) with residual hemiparetic gait were enrolled >6 months after stroke. Participants were randomized to receive 3 months (3×/week) progressive graded, high-intensity aerobic treadmill exercise (TAEX) or conventional care physiotherapy. Primary outcome measures were peak exercise capacity (Vo(2peak)) and sustained walking capacity in 6-minute walks (6MW). Secondary measures were gait velocity in 10-m walks, Berg Balance Scale, functional leg strength (5 chair-rise), self-rated mobility (Rivermead Mobility Index), and quality of life (SF-12). RESULTS: Thirty-six participants completed the study (18 TAEX, 18 controls). TAEX but not conventional care improved Vo(2peak) (difference 6.4 mL/kg/min, P < .001) and 6MW (53 m, P < .001). Likewise, maximum walking speed (0.13 m/s, P = .01), balance (P < .05), and the mental subscore of the SF-12 (P < .01) improved more after TAEX. Gains in Vo(2peak) correlated with the degree at which training intensity could be progressed in the individual participant (P < .01). Better walking was related to progression in treadmill velocity and training duration (P < .001). Vo(2peak) and 6MW performances were still higher 1 year after the end of training when compared with the baseline, although endurance walking (6MW) at 1 year was lower than immediately after training (P < .01). CONCLUSION: This trial demonstrates that TAEX effectively improves cardiovascular fitness and gait in persons with chronic stroke.

Mesencephalic corticospinal atrophy predicts baseline deficit but not response to unilateral or bilateral arm training in chronic stroke.

OBJECTIVE: Stroke survivors with motor deficits often have pyramidal tract atrophy caused by degeneration of corticospinal fibers. The authors hypothesized that the degree of atrophy correlates with severity of motor impairment in patients with chronic stroke and predicts the response to rehabilitation training. METHODS: They performed a post hoc analysis of 42 hemiparetic patients (>6 months) who had been randomized to either 6 weeks of bilateral arm training with rhythmic auditory cueing (BATRAC) or dose-matched therapeutic exercise (DMTE). Arm function was measured using the Fugl-Meyer (FM) and modified Wolf Motor Function Test (WMFT). Structural MRI and diffusion tensor imaging (DTI) on the pontine level measured corticospinal tract (CST) atrophy by planimetric measurement of the mesencephalon (mesencephalic atrophy ratio) and fractional anisotropy (FA), respectively. Voxel-based lesion symptom mapping (VLSM) was used to determine the lesions associated with highest degrees of atrophy. The predictive value of CST atrophy for impairment and training response was analyzed. RESULTS: CST atrophy predicted baseline motor arm function measured by the FM and WMFT. The authors found only a trend for the correlation with FA. No measure of atrophy predicted response to either BATRAC or DMTE. CST atrophy was higher with larger lesions and those that affected the CST. VLSM identified internal capsule lesions as being associated with highest CST atrophy. CONCLUSION: Larger lesions, internal capsule lesions, and those overlapping the pyramidal tract are associated with greater CST atrophy. CST atrophy explains in part the variability of baseline deficits but does not seem to predict the response to BATRAC or unilateral arm training on upper-extremity function.

Predictors of response to treadmill exercise in stroke survivors.

BACKGROUND: Aerobic treadmill exercise (T-EX) therapy has been shown to benefit walking and cardiorespiratory fitness in stroke survivors with chronic gait impairment even long after their stroke. The response, however, varies between individuals. OBJECTIVE: The purpose of this post hoc analysis of 2 randomized controlled T-EX trials was to identify predictors for therapy response. METHODS: In all, 52 participants received T-EX for 3 (Germany) or 6 (United States) months. Improvements in overground walking velocity (10 m/6-min walk) and fitness (peak VO(2)) were indicators of therapy response. Lesion location and volume were measured on T1-weighted magnetic resonance scans. RESULTS: T-EX significantly improved gait and fitness, with gains in 10-m walk tests ranging between +113% and -25% and peak VO(2) between -12% and 88%. Baseline walking impairments or fitness deficits were not predictive of therapy response; 10-m walk velocity improved more in those with subcortical rather than cortical lesions and in patients with smaller lesions. Improvements in 6-minute walk velocity were greater in those with more recent strokes and left-sided lesions. No variable other than training intensity, which was different between trials, predicted fitness gains. CONCLUSIONS: Despite proving overall effectiveness, the response to T-EX varies markedly between individuals. Whereas intensity of aerobic training seems to be an important predictor of gains in cardiovascular fitness, lesion size and location as well as interval between stroke onset and therapy delivery likely affect therapy response. These findings may be used to guide the timing of training and identify subgroups of patients for whom training modalities could be optimized.

Bayesian motion estimation accounts for a surprising bias in 3D vision.

Determining the approach of a moving object is a vital survival skill that depends on the brain combining information about lateral translation and motion-in-depth. Given the importance of sensing motion for obstacle avoidance, it is surprising that humans make errors, reporting an object will miss them when it is on a collision course with their head. Here we provide evidence that biases observed when participants estimate movement in depth result from the brain's use of a "prior" favoring slow velocity. We formulate a Bayesian model for computing 3D motion using independently estimated parameters for the shape of the visual system's slow velocity prior. We demonstrate the success of this model in accounting for human behavior in separate experiments that assess both sensitivity and bias in 3D motion estimation. Our results show that a surprising perceptual error in 3D motion perception reflects the importance of prior probabilities when estimating environmental properties.

Neural coding of global form in the human visual cortex.

Extensive psychophysical and computational work proposes that the perception of coherent and meaningful structures in natural images relies on neural processes that convert information about local edges in primary visual cortex to complex object features represented in the temporal cortex. However, the neural basis of these mid-level vision mechanisms in the human brain remains largely unknown. Here, we examine functional MRI (fMRI) selectivity for global forms in the human visual pathways using sensitive multivariate analysis methods that take advantage of information across brain activation patterns. We use Glass patterns, parametrically varying the perceived global form (concentric, radial, translational) while ensuring that the local statistics remain similar. Our findings show a continuum of integration processes that convert selectivity for local signals (orientation, position) in early visual areas to selectivity for global form structure in higher occipitotemporal areas. Interestingly, higher occipitotemporal areas discern differences in global form structure rather than low-level stimulus properties with higher accuracy than early visual areas while relying on information from smaller but more selective neural populations (smaller voxel pattern size), consistent with global pooling mechanisms of local orientation signals. These findings suggest that the human visual system uses a code of increasing efficiency across stages of analysis that is critical for the successful detection and recognition of objects in complex environments.