Maximilian J. Wessel

Non-invasive brain stimulation: an interventional tool for enhancing behavioral training after stroke.

Stroke is the leading cause of disability among adults. Motor deficit is the most common impairment after stroke. Especially, deficits in fine motor skills impair numerous activities of daily life. Re-acquisition of motor skills resulting in improved or more accurate motor performance is paramount to regain function, and is the basis of behavioral motor therapy after stroke. Within the past years, there has been a rapid technological and methodological development in neuroimaging leading to a significant progress in the understanding of the neural substrates that underlie motor skill acquisition and functional recovery in stroke patients. Based on this and the development of novel non-invasive brain stimulation (NIBS) techniques, new adjuvant interventional approaches that augment the response to behavioral training have been proposed. Transcranial direct current, transcranial magnetic, and paired associative (PAS) stimulation are NIBS techniques that can modulate cortical excitability, neuronal plasticity and interact with learning and memory in both healthy individuals and stroke patients. These techniques can enhance the effect of practice and facilitate the retention of tasks that mimic daily life activities. The purpose of the present review is to provide a comprehensive overview of neuroplastic phenomena in the motor system during learning of a motor skill, recovery after brain injury, and of interventional strategies to enhance the beneficial effects of customarily used neurorehabilitation after stroke.

Parietofrontal motor pathways and their association with motor function after stroke

Corticocortical interactions between the primary motor cortex, the ventral premotor cortex and posterior parietal motor areas, such as the anterior and caudal intraparietal sulcus, are relevant for skilled voluntary hand function. It remains unclear to what extent these brain regions and their interactions also contribute to basic motor functions after stroke. We hypothesized that white matter integrity of the underlying parietofrontal motor pathways between these brain regions might relate to residual motor function after stroke. Twenty-five chronic stroke patients were recruited (aged 64 ± 8.8 years, range 46-75, 17 males, one left-handed) and evaluated 34 months after stroke (range 12-169 months) by means of grip force, pinch force and the Fugl-Meyer assessment of the upper extremity. Based on these measures, motor function was estimated applying a factor analysis with principal component extraction. Using diffusion tensor imaging and probabilistic tractography we reconstructed probable intrahemispheric trajectories between the primary motor cortex, the ventral premotor cortex and the anterior and caudal intraparietal sulcus in each patient. White matter integrity was estimated for each individual tract by means of fractional anisotropy. Generalized linear modelling was used to relate tract-related fractional anisotropy to the motor function. We found that the white matter integrity of the fibre tracts connecting the ventral premotor cortex and the primary motor cortex (P < 0.001) and the anterior intraparietal sulcus and the ventral premotor cortex (P < 0.01) positively correlated with motor function. The other tracts investigated did not show a similar structure-behaviour association. Providing first structural connectivity data for parietofrontal connections in chronic stroke patients, the present results indicate that both the ventral premotor cortex and the posterior parietal cortex might play a relevant role in generating basic residual motor output after stroke.

Enhancing Consolidation of a New Temporal Motor Skill by Cerebellar Noninvasive Stimulation

Cerebellar transcranial direct current stimulation (tDCS) has the potential to modulate cerebellar outputs and visuomotor adaptation. The cerebellum plays a pivotal role in the acquisition and control of skilled hand movements, especially its temporal aspects. We applied cerebellar anodal tDCS concurrently with training of a synchronization-continuation motor task. We hypothesized that anodal cerebellar tDCS will enhance motor skill acquisition. Cerebellar tDCS was applied to the right cerebellum in 31 healthy subjects in a double-blind, sham-controlled, parallel design. During synchronization, the subjects tapped the sequence in line with auditory cues. Subsequently, in continuation, the learned sequence was reproduced without auditory cuing. Motor task performance was evaluated before, during, 90 min, and 24 h after training. Anodal cerebellar tDCS, compared with sham, improved the task performance in the follow-up tests (F1,28 = 5.107, P = 0.032) of the synchronization part. This effect on retention of the skill was most likely mediated by enhanced motor consolidation. We provided first evidence that cerebellar tDCS can enhance the retention of a fine motor skill. This finding supports the promising approach of using noninvasive brain stimulation techniques to restore impaired motor functions in neurological patients, such after a stroke.

White Matter Integrity of Specific Dentato-Thalamo-Cortical Pathways is Associated with Learning Gains in Precise Movement Timing

The dentato-thalamo-cortical tract (DTCT) connects the lateral cerebellum with contralateral motor and nonmotor areas, such as the primary motor cortex (M1), the ventral premotor cortex (PMv), and the dorsolateral prefrontal cortex (DLPFC). As the acquisition of precisely timed finger movements requires the interplay between these brain regions, the structural integrity of the underlying connections might explain variance in behavior. Diffusion tensor imaging was used to 1) reconstruct the DTCT connecting the dentate nucleus with M1, PMv, and DLPFC and 2) examine to which extent their microstructural integrity (tract-related fractional anisotropy) relates to learning gains in a motor-sequence learning paradigm consisting of a synchronization and continuation part. Continuous DTCT were reconstructed from the dentate nucleus to all cortical target areas. We found that the microstructural integrity of the DTCT connecting the left dentate nucleus with the right DLPFC was associated with better early consolidation in rhythm continuation (R = -0.69, P = 0.02). The present data further advances the knowledge about a right-hemispheric timing network in the human brain with the DLPFC as an important node contributing to learning gains in precise movement timing.

White matter integrity of motor connections related to training gains in healthy aging

Impaired motor skill acquisition is a feature of older age. Acquisition of new motor skills requires the interplay between different cortical motor areas. Using diffusion tensor imaging we reconstructed cortico-cortical connections between the primary motor cortex (M1) and secondary motor areas in 11 older and 11 young participants who took part in a motor skill acquisition paradigm with the nondominant left hand. Examining the extent to which tract-related integrity correlated with training gains we found that white matter integrity of fibers connecting contralateral M1 with both contralateral (r = 0.85) and ipsilateral supplementary motor areas (r = 0.92) were positively associated in old participants. Also, fibers connecting contralateral M1 with ipsilateral dorsal premotor (r = 0.82) and fibers connecting ipsilateral dorsal premotor and supplementary motor area (r = 0.88) were positively related to skill acquisition (all p < 0.05). A similar structure-behavior relationship was not present in the young control subjects suggesting a critical role of brain structural integrity for motor learning in healthy aging.

Impairment of Procedural Learning and Motor Intracortical Inhibition in Neurofibromatosis Type 1 Patients

Background Cognitive difficulties are the most common neurological complications in neurofibromatosis type 1 (NF1) patients. Recent animal models proposed increased GABA-mediated inhibition as one underlying mechanism directly affecting the induction of long-term potentiation (LTP) and learning. In most adult NF1 patients, apparent cognitive and attentional deficits, tumors affecting the nervous system and other confounding factors for neuroscientific studies are difficult to control for. Here we used a highly specific group of adult NF1 patients without cognitive or nervous system impairments. Such selected NF1 patients allowed us to address the following open questions: Is the learning process of acquiring a challenging motor skill impaired in NF1 patients? And is such an impairment in relation to differences in intracortical inhibition? Methods We used an established non-invasive, double-pulse transcranial magnetic stimulation (dp-TMS) paradigm to assess practice-related modulation of intracortical inhibition, possibly mediated by gamma-minobutyric acid (GABA)ergic-neurotransmission. This was done during an extended learning paradigm in a group of NF1 patients without any neuropsychological deficits, functioning normally in daily life and compared them to healthy age-matched controls. Findings NF1 patients experienced substantial decline in motor skill acquisition (F = 9.2, p = 0.008) over five-consecutives training days mediated through a selective reduction in the early acquisition (online) and the consolidation (offline) phase. Furthermore, there was a consistent decrease in task-related intracortical inhibition as a function of the magnitude of learning (T = 2.8, p = 0.014), especially evident after the early acquisition phase. Interpretations Collectively, the present results provide evidence that learning of a motor skill is impaired even in clinically intact NF1 patients based, at least partially, on a GABAergic-cortical dysfunctioning as suggested in previous animal work.

Non-invasive Cerebellar Stimulation: a Promising Approach for Stroke Recovery?

Non-invasive brain stimulation (NIBS) combined with behavioral training is a promising strategy to augment recovery after stroke. Current research efforts have been mainly focusing on primary motor cortex (M1) stimulation. However, the translation from proof-of-principle to clinical applications is not yet satisfactory. Possible reasons are the heterogeneous properties of stroke, generalization of the stimulation protocols, and hence the lack of patient stratification. One strategy to overcome these limitations could be the evaluation of alternative stimulation targets, like the cerebellum. In this regard, first studies provided evidence that non-invasive cerebellar stimulation can modulate cerebellar processing and linked behavior in healthy subjects. The cerebellum provides unique plasticity mechanisms and has vast connections to interact with neocortical areas. Moreover, the cerebellum could serve as a non-lesioned entry to the motor or cognitive system in supratentorial stroke. In the current article, we review mechanisms of plasticity in the cortico-cerebellar system after stroke, methods for non-invasive cerebellar stimulation, and possible target symptoms in stroke, like fine motor deficits, gait disturbance, or cognitive impairments, and discuss strategies for multi-focal stimulation.

Eyelid myokymia in an older subject after repetitive sessions of anodal transcranial direct current stimulation.

Note: Letter Reference EPFL-ARTICLE-223949doi:10.1016/j.brs.2012.09.002 Record created on 2016-12-27, modified on 2016-12-27

Iterative Design of an Upper Limb Rehabilitation Game with Tangible Robots

Rehabilitation aims to ameliorate deficits in motor control via intensive practice with the affected limb. Current strategies, such as one-on-one therapy done in rehabilitation centers, have limitations such as treatment frequency and intensity, cost and requirement of mobility. Thus, a promising strategy is home-based therapy that includes task specific exercises. However, traditional rehabilitation tasks may frustrate the patient due to their repetitive nature and may result in lack of motivation and poor rehabilitation. In this article, we propose the design and verification of an effective upper extremity rehabilitation game with a tangible robotic platform named Cellulo as a novel solution to these issues. We first describe the process of determining the design rationales to tune speed, accuracy and challenge. Then we detail our iterative participatory design process and test sessions conducted with the help of stroke, brachial plexus and cerebral palsy patients (18 in total) and 7 therapists in 4 different therapy centers. We present the initial quantitative results, which support several aspects of our design rationales and conclude with our future study plans.

Non-invasive brain stimulation to enhance cognitive rehabilitation after stroke

Stroke is a main cause for long-term disability. Stroke symptoms cover various domains, e.g., motor, sensory, language, or other cognitive functions. In clinical practice and rehabilitation research, especially motor impairment attracts much attention. However, also cognitive impairments are common after stroke, effecting approximately two-thirds of stroke patients in the acute phase. Although 30% of stroke patients spontaneously recover from their cognitive impairments, large amounts of patients remain cognitively impaired. These patients have more problems reintegrating in personal and professional life. To date, cognitive rehabilitation strategies are not yet satisfactory. One promising strategy is combining non-invasive brain stimulation (NIBS) with cognitive training. In the current review, we will discuss the relevance of cognitive impairment after stroke and innovative interventional strategies to improve cognition, such as NIBS. Furthermore, we will address the potential of using cognitive training to enhance recovery in other behavioural domains, such as the motor domain.