Motor learning processes in a movement-scaling task in olivopontocerebellar atrophy and Parkinson's disease

Motor Memory Consolidation Deficits in Parkinson's Disease: A Systematic Review with Meta-Analysis

BACKGROUND

The ability to encode and consolidate motor memories is essential for persons with Parkinson's disease (PD), who usually experience a progressive loss of motor function. Deficits in memory encoding, usually expressed as poorer rates of skill improvement during motor practice, have been reported in these patients. Whether motor memory consolidation (i.e., motor skill retention) is also impaired is unknown.

OBJECTIVE

To determine whether motor memory consolidation is impaired in PD compared to neurologically intact individuals.

METHODS

We conducted a pre-registered systematic review (PROSPERO: CRD42020222433) following PRISMA guidelines that included 46 studies.

RESULTS

Meta-analyses revealed that persons with PD have deficits in retaining motor skills (SMD = -0.17; 95% CI = -0.32, -0.02; p = 0.0225). However, these deficits are task-specific, affecting sensory motor (SMD = -0.31; 95% CI -0.47, -0.15; p = 0.0002) and visuomotor adaptation (SMD = -1.55; 95% CI = -2.32, -0.79; p = 0.0001) tasks, but not sequential fine motor (SMD = 0.17; 95% CI = -0.05, 0.39; p = 0.1292) and gross motor tasks (SMD = 0.04; 95% CI = -0.25, 0.33; p = 0.7771). Importantly, deficits became non-significant when augmented feedback during practice was provided, and additional motor practice sessions reduced deficits in sensory motor tasks. Meta-regression analyses confirmed that deficits were independent of performance during encoding, as well as disease duration and severity.

CONCLUSION

Our results align with the neurodegenerative models of PD progression and motor learning frameworks and emphasize the importance of developing targeted interventions to enhance motor memory consolidation in PD.

Genetically engineered mesenchymal stem cells with dopamine synthesis for Parkinson's disease in animal models

Although striatal delivery of three critical genes for dopamine synthesis by viruses is a potential clinical approach for treating Parkinson's disease (PD), the approach makes it difficult to finely control dopamine secretion amounts and brings safety concerns. Here, we generate genetically engineered mesenchymal stem cells encoding three critical genes for dopamine synthesis (DOPA-MSCs). DOPA-MSCs retain their MSC identity and stable ability to secrete dopamine during passaging. Following transplantation, DOPA-MSCs reinstate striatal dopamine levels and correct motor function in PD rats. Importantly, after grafting into the caudate and putamen, DOPA-MSCs provide homotopic reconstruction of midbrain dopamine pathways by restoring striatal dopamine levels, and safely and long-term (up to 51 months) correct motor disorders and nonmotor deficits in acute and chronic PD rhesus monkey models of PD even with advanced PD symptoms. The long-term benefits and safety results support the idea that the development of dopamine-synthesized engineered cell transplantation is an important strategy for treating PD.

Targeting thalamic circuits rescues motor and mood deficits in PD mice

Although bradykinesia, tremor and rigidity are the hallmark motor defects in patients with Parkinson's disease (PD), patients also experience motor learning impairments and non-motor symptoms such as depression¹. The neural circuit basis for these different symptoms of PD are not well understood. Although current treatments are effective for locomotion deficits in PD^2,3, therapeutic strategies targeting motor learning deficits and non-motor symptoms are lacking^4-6. Here we found that distinct parafascicular (PF) thalamic subpopulations project to caudate putamen (CPu), subthalamic nucleus (STN) and nucleus accumbens (NAc). Whereas PF→CPu and PF→STN circuits are critical for locomotion and motor learning, respectively, inhibition of the PF→NAc circuit induced a depression-like state. Whereas chemogenetically manipulating CPu-projecting PF neurons led to a long-term restoration of locomotion, optogenetic long-term potentiation (LTP) at PF→STN synapses restored motor learning behaviour in an acute mouse model of PD. Furthermore, activation of NAc-projecting PF neurons rescued depression-like phenotypes. Further, we identified nicotinic acetylcholine receptors capable of modulating PF circuits to rescue different PD phenotypes. Thus, targeting PF thalamic circuits may be an effective strategy for treating motor and non-motor deficits in PD.

Parkinson's disease: Alterations of motor plasticity and motor learning

This chapter reviews the alterations in motor learning and motor cortical plasticity in Parkinson's disease (PD), the most common movement disorder. Impairments in motor learning, which is a hallmark of basal ganglia disorders, influence the performance of motor learning-related behavioral tasks and have clinical implications for the management of disturbance in gait and posture, and for rehabilitative management of PD. Although plasticity is classically induced and assessed in sliced preparation in animal models, in this review we have concentrated on the results from non-invasive brain stimulation techniques such as transcranial magnetic stimulation (TMS), transcranial alternating current stimulation (tACS) and transcranial direct current stimulation (tDCS) in patients with PD, in addition to a few animal electrophysiologic studies. The chapter summarizes the results from different cortical and subcortical plasticity investigations. Plasticity induction protocols reveal deficient plasticity in PD and these plasticity measures are modulated by medications and deep brain stimulation. There is considerable variability in these measures that are related to inter-individual variations, different disease characteristics and methodological considerations. Nevertheless, these pathophysiologic studies expand our knowledge of cortical excitability, plasticity and the effects of different treatments in PD. These tools of modulating plasticity and motor learning improve our understanding of PD pathophysiology and help to develop new treatments for this disabling condition.

Reduced striatal dopamine release during motor skill acquisition in Parkinson's disease

Background

Striatal dopamine is functionally important for the acquisition of motor skills. However, it remains controversial as to whether intrinsic processing of motor learning is impaired in patients with Parkinson’s disease (PD), and if yes, whether the impairment is associated with altered striatal dopamine release. Additionally, most neuro-imaging studies of patients with PD have focused on motor sequence learning. In contrast, skill acquisition, specifically, the reconstruction of muscle control of isolated movements, has barely been studied.

Method

In this study, we used a repetitive skill training task to measure the peak acceleration of left thumb movement during a process to achieve fine tuning of motor skill. Using ¹¹C-raclopride (RAC) positron emission tomography, we investigated changes in striatal dopamine levels in two conditions of a skill acquisition task: initial skill training (Day 1) and acquired condition (Day 2) with eight patients with PD and age-matched healthy subjects (HS).

Result

In HS, the mean acceleration of each session improved through repeated training sessions on Day 1. However, in patients with PD, the training-associated increase was less than that for HS, and this suggests that repetitive skill training does not result in the effective improvement of motor performance. The regions of interest (ROI) analysis revealed that the RAC-binding potential (BP) was significantly reduced in the right putamen on Day 1 compared with Day 2 in HS. In patients with PD, BP within the right putamen was unchanged. Further, we found that patients with PD had increased dopamine levels within the right ventral striatum (VST) and right caudate (CAU) on Day 2, which was greater than that in HS. These results suggest the impaired activation of the putamen during skill acquisition in patients with PD and compensated hyperactivation of the VST and CAU for the reduced dopamine release within the dorsal putamen (DPU).

Conclusion

Our findings suggest that patients with PD had insufficiency in the process to improve motor skills. Different patterns of striatal dopamine release are relevant to the impairment of these motor functions in patients with PD, at the early stage of the disease.

Learning "How to Learn": Super Declarative Motor Learning Is Impaired in Parkinson's Disease

Learning new information is crucial in daily activities and occurs continuously during a subject's lifetime. Retention of learned material is required for later recall and reuse, although learning capacity is limited and interference between consecutively learned information may occur. Learning processes are impaired in Parkinson's disease (PD); however, little is known about the processes related to retention and interference. The aim of this study is to investigate the retention and anterograde interference using a declarative sequence learning task in drug-naive patients in the disease's early stages. Eleven patients with PD and eleven age-matched controls learned a visuomotor sequence, SEQ1, during Day1; the following day, retention of SEQ1 was assessed and, immediately after, a new sequence of comparable complexity, SEQ2, was learned. The comparison of the learning rates of SEQ1 on Day1 and SEQ2 on Day2 assessed the anterograde interference of SEQ1 on SEQ2. We found that SEQ1 performance improved in both patients and controls on Day2. Surprisingly, controls learned SEQ2 better than SEQ1, suggesting the absence of anterograde interference and the occurrence of learning optimization, a process that we defined as “learning how to learn.” Patients with PD lacked such improvement, suggesting defective performance optimization processes.

The many facets of motor learning and their relevance for Parkinson's disease

The final goal of motor learning, a complex process that includes both implicit and explicit (or declarative) components, is the optimization and automatization of motor skills. Motor learning involves different neural networks and neurotransmitters systems depending on the type of task and on the stage of learning. After the first phase of acquisition, a motor skill goes through consolidation (i.e., becoming resistant to interference) and retention, processes in which sleep and long-term potentiation seem to play important roles. The studies of motor learning in Parkinson's disease have yielded controversial results that likely stem from the use of different experimental paradigms. When a task's characteristics, instructions, context, learning phase and type of measures are taken into consideration, it is apparent that, in general, only learning that relies on attentional resources and cognitive strategies is affected by PD, in agreement with the finding of a fronto-striatal deficit in this disease. Levodopa administration does not seem to reverse the learning deficits in PD, while deep brain stimulation of either globus pallidus or subthalamic nucleus appears to be beneficial. Finally and most importantly, patients with PD often show a decrease in retention of newly learned skill, a problem that is present even in the early stages of the disease. A thorough dissection and understanding of the processes involved in motor learning is warranted to provide solid bases for effective medical, surgical and rehabilitative approaches in PD.

Virtual Normalization of Physical Impairment: A Pilot Study to Evaluate Motor Learning in Presence of Physical Impairment

Motor learning is a critical component of the rehabilitation process; however, it can be difficult to separate the fundamental causes of a learning deficit when physical impairment is a confounding factor. In this paper, a new technique is proposed to augment the residual ability of physically impaired patients with a robotic rehabilitation exoskeleton, such that motor learning can be studied independently of physical impairment. The proposed technique augments the velocity of an on-screen cursor relative to the restricted physical motion. Radial Basis Functions (RBFs) are used to both model velocity and derive a function to scale velocity as a function of workspace position. Two variations of the algorithm are presented for comparison. In a cross-over pilot study, healthy participants were recruited and subjected to a simulated impairment to constrain their motion, imposed by the cable-driven wrist exoskeleton. Participants then completed a sinusoidal tracking task, in which the algorithms were statistically shown to augment the cursor velocity in the constrained state such that it matched position-dependent velocities recorded in the healthy state. A kinematic task was then designed as a motor-learning case study where the algorithms were statistically shown to allow participants to achieve the same performance when their motion was constrained as when unconstrained. The results of the pilot study provide motivation for further research into the use of this technique, thus providing a tool with which motor-learning can be studied in neurologically impaired populations. This could be used to give physiotherapists greater insight into underlying causes of motor learning deficits, consequently facilitating and enhancing subject-specific therapy regimes.

Motor Learning and Parkinson Disease: Refinement of Movement Velocity and Endpoint Excursion in a Limits of Stability Balance Task

Objective. To investigate the effects of practice on performance and retention of a balance task in persons with Parkinson disease (PD).

Methods. Ten persons with PD and 10 age and gender-matched healthy control subjects were tested on an anticipatory, static base of support, limits of stability (LOS) balance task on a force plate. The motor learning paradigm utilized for all subjects included an acquisition phase and retention tests at 24 h and 1 week after acquisition. A force plate was used for testing and to collect outcome measures including movement velocity (MVL), endpoint excursion (EPE), and directional control. Data were analyzed for differences between groups and change over time.

Results.Persons with PD demonstrated performance deficits relative to controls for MVL at all testing periods ( P < 0.05), and initially for EPE ( P < 0.05), but were able to maintain significant improvements through retention testing relative to baseline ( P < 0.05).

Conclusions. Persons with PD demonstrated unimpaired capacity for motor learning in a LOS balance task for MVL and EPE, although performance deficits remained for MVL. The results concur with previous motor learning research of upper extremity tasks by suggesting that individuals with mild to moderate PD exhibit a preserved ability to benefit from practice as a means of improving balance task performance.

Differences in dopaminergic modulation to motor cortical plasticity between Parkinson's disease and multiple system atrophy

Dopamine modulates the synaptic plasticity in the primary motor cortex (M1). To evaluate whether the functioning of the cortico-striatal circuit is necessary for this modulation, we applied a paired associative stimulation (PAS) protocol that comprised an electric stimulus to the right median nerve at the wrist and subsequent transcranial magnetic stimulation of the left M1, to 10 patients with Parkinson's disease (PD) and 10 with multiple system atrophy of the parkinsonian type (MSA-P) with and without dopamine replacement therapy (-on/off). To investigate the M1 function, motor-evoked potentials (MEPs) were measured before and after the PAS. In both patient groups without medication, the PAS protocol failed to increase the averaged amplitude of MEPs. The dopamine replacement therapy in PD, but not in MSA-P effectively restored the PAS-induced MEP increase. This suggests that not the existence of dopamine itself but the activation of cortico-striatal circuit might play an important role for cortical plasticity in the human M1.

Quantitative assessment of motor abnormalities in untreated patients with major depressive disorder

The primary purpose of this study was to examine motor physiology disturbances in a group of patients with untreated major depressive disorder using sensitive instrumental procedures. The secondary aim of the study was to examine the relationship of the affective symptom state to these motor assessments. The authors studied 40 individuals meeting DSM-IV criteria for unipolar major depressive disorder and 40 healthy comparison subjects. Electromechanical measures of force steadiness (FS), simple reaction time (RT), movement time (MT) and scaling of movement velocity to distance (velocity scaling, VS) were performed. The authors found that performance on the force steadiness, movement time, and velocity scaling measures was significantly poorer in the subjects with depression. There was no difference between the groups on the measure of reaction time. The force steadiness, reaction time, movement time, and velocity scaling scores were not associated with affective state. This study demonstrates that motor abnormalities suggestive of basal ganglia dysfunction occur in many patients with major depressive disorder, and that these abnormalities may exist in the absence of current psychotropic medication treatment. The finding of impaired movement time and velocity scaling in the presence of normal reaction time suggests a neuromotor or parkinsonian pathophysiology for slowness in depression.

The influence of movement initiation deficits on the quantification of retention in Parkinson's disease

In patients with an impaired motor system, like Parkinson’s disease (PD), deficits in motor learning are expected and results of various studies seem to confirm these expectations. However, most studies in this regard are behaviorally based and quantify learning by performance changes between at least two points in time, e.g., baseline and retention. But, performance in a retention test is also dependent on other factors than learning. Especially in patients, the functional capacity of the control system might be altered unspecific to a certain task and learning episode. The aim of the study is to test whether characteristic temporal deficits exist in PD patients that affect retention performance. We tested the confounding effects of typical PD motor control deficits, here movement initiation deficits, on retention performance in the motor learning process. 12 PD patients and 16 healthy control participants practiced a virtual throwing task over 3 days with 24 h rest between sessions. Retention was tested comparing performance before rest with performance after rest. Movement initiation deficits were quantified by the timing of throwing release that should be affected by impairments in movement initiation. To scrutinize the influence of the initiation deficits on retention performance we gave participants a specific initiation intervention prior to practice on one of the three practice days. We found that only for the PD patients, post-rest performance as well as release timing was better with intervention as compared to without intervention. Their performance could be enhanced through a tuning of release initiation. Thus, we suggest that in PD patients, performance decline after rest that might be easily interpreted as learning deficits could rather result from disease-related deficiencies in motor control.

Cerebellar Ataxia Rehabilitation Trial in Degenerative Cerebellar Diseases

Objective. To investigate short- and long-term effects of intensive rehabilitation on ataxia, gait, and activities of daily living (ADLs) in patients with degenerative cerebellar disease. Methods. A total of 42 patients with pure cerebellar degeneration were randomly assigned to the immediate group or the delayed-entry control group. The immediate group received 2 hours of inpatient physical and occupational therapy, focusing on coordination, balance, and ADLs, on weekdays and 1 hour on weekends for 4 weeks. The control group received the same intervention after a 4-week delay. Short-term outcome was compared between the immediate and control groups. Long-term evaluation was done in both groups at 4, 12, and 24 weeks after the intervention. Outcome measures included the assessment and rating of ataxia, Functional Independence Measure, gait speed, cadence, functional ambulation category, and number of falls. Results. The immediate group showed significantly greater functional gains in ataxia, gait speed, and ADLs than the control group. Improvement of truncal ataxia was more prominent than limb ataxia. The gains in ataxia and gait were sustained at 12 weeks and 24 weeks, respectively. At least 1 measure was better than at baseline at 24 weeks in 22 patients. Conclusions. Short-term benefit of intensive rehabilitation was evident in patients with degenerative cerebellar diseases. Although functional status tended to decline to the baseline level within 24 weeks, gains were maintained in more than half of the participants.

Motor Skill Learning, Retention, and Control Deficits in Parkinson's Disease

Parkinson's disease, which affects the basal ganglia, is known to lead to various impairments of motor control. Since the basal ganglia have also been shown to be involved in learning processes, motor learning has frequently been investigated in this group of patients. However, results are still inconsistent, mainly due to skill levels and time scales of testing. To bridge across the time scale problem, the present study examined de novo skill learning over a long series of practice sessions that comprised early and late learning stages as well as retention. 19 non-demented, medicated, mild to moderate patients with Parkinson's disease and 19 healthy age and gender matched participants practiced a novel throwing task over five days in a virtual environment where timing of release was a critical element. Six patients and seven control participants came to an additional long-term retention testing after seven to nine months. Changes in task performance were analyzed by a method that differentiates between three components of motor learning prominent in different stages of learning: Tolerance, Noise and Covariation. In addition, kinematic analysis related the influence of skill levels as affected by the specific motor control deficits in Parkinson patients to the process of learning. As a result, patients showed similar learning in early and late stages compared to the control subjects. Differences occurred in short-term retention tests; patients' performance constantly decreased after breaks arising from poorer release timing. However, patients were able to overcome the initial timing problems within the course of each practice session and could further improve their throwing performance. Thus, results demonstrate the intact ability to learn a novel motor skill in non-demented, medicated patients with Parkinson's disease and indicate confounding effects of motor control deficits on retention performance.

Learning and consolidation of visuo-motor adaptation in Parkinson's disease

We have previously shown in normal subjects that motor adaptation to imposed visual rotation is significantly enhanced when tested few days later. This occurs through a process of sleep-dependent memory consolidation. Here we ascertained whether patients with Parkinson's disease (PD) learn, improve, and retain new motor skills in the same way as normal subjects. We tested 16 patients in early stages of PD and 21 control subjects over two days. All subjects performed reaching movements on a digitizing tablet. Vision of the limb was precluded with an opaque screen; hand paths were shown on the screen with the targets' position. Unbeknownst to the subjects, the hand path on the screen was rotated by 30 degrees . In experiment 1, patients taking dopaminergic treatment and controls adapted to rotation with targets appearing in an unpredictable order. In experiment 2, drug-naïve patients and controls adapted to rotation in a less challenging task where target's appearance was predictable. Patients and controls made similar movements and adapted to rotation in the same way. However, when tested again over the following days, controls' performance significantly improved compared to training, while patients' performance did not. This lack of consolidation, which is present in the early stages of the disease and is independent from therapy, may be due to abnormal homeostatic processes that occur during sleep.

Sequence skill learning in persons who stutter: implications for cortico-striato-thalamo-cortical dysfunction

The basal ganglia and cortico-striato-thalamo-cortical connections are known to play a critical role in sequence skill learning and increasing automaticity over practice. The current paper reviews four studies comparing the sequence skill learning and the transition to automaticity of persons who stutter (PWS) and fluent speakers (PNS) over practice. Studies One and Two found PWS to have poor finger tap sequencing skill and nonsense syllable sequencing skill after practice, and on retention and transfer tests relative to PNS. Studies Three and Four found PWS to be significantly less accurate and/or significantly slower after practice on dual tasks requiring concurrent sequencing and colour recognition over practice relative to PNS. Evidence of PWS' deficits in sequence skill learning and automaticity development support the hypothesis that dysfunction in cortico-striato-thalamo-cortical connections may be one etiological component in the development and maintenance of stuttering.

EDUCATIONAL OBJECTIVES

As a result of this activity, the reader will: (1) be able to articulate the research regarding the basal ganglia system relating to sequence skill learning; (2) be able to summarize the research on stuttering with indications of sequence skill learning deficits; and (3) be able to discuss basal ganglia mechanisms with relevance for theory of stuttering.

Predictors of driving assessment outcome in Parkinson's disease

This study evaluated selected clinical and functional tests as predictors of driving safety outcomes in Parkinson's disease (PD) patients. A total of 25 PD patients and 21 age-matched controls, all regular drivers, underwent neurological evaluation and assessment of cognitive, visual, and motor function and a standardized, on-road driving assessment. The capacity of the tests to predict pass/fail driving outcomes was determined by selecting a subset with the highest predictive value from each domain and then subjecting these subsets to discriminant function analysis. Accuracy, sensitivity, specificity, and positive and negative predictive values were determined. Three relatively simple tests from the larger battery predicted passes with relatively high sensitivity (PD, 72.7%; controls, 93.8%; both combined, 85.2%); and moderate specificity (PD, 64.3%; controls, 60.0%; both combined. 63.2%). These tests assessed motor performance (Purdue Pegboard test), contrast sensitivity (Pelli-Robson test), and cognitive function (verbal version of Symbol Digit Modalities test). Adding time since diagnosis for the PD group increased sensitivity to 90.9% and specificity to 71.4%. These simple tests confer more objectivity and predictive power to clinical recommendations for driving, they reflect distinct functions that are necessary for safe driving, and they may be especially useful when on-road assessments are not feasible.

TMS-assisted neurophysiological profiling of the dopamine receptor agonist cabergoline in human motor cortex

Dopamine plays a broad role in motor control and practice-dependent plasticity. Here we tested, in eight healthy subjects, the effects of the dopamine receptor agonist cabergoline on motor cortical excitability because the state of motor cortex can strongly influence practice-dependent plasticity. Cabergoline enhances practice-dependent plasticity but the mechanisms are unknown. We used transcranial magnetic stimulation for testing of motor cortical excitability. A single dose of 2 mg of cabergoline increased short-interval intracortical inhibition, a measure of excitability of GABA-dependent inhibitory neural circuits, and decreased various excitatory measures (motor evoked potential amplitude and short-interval intracortical facilitation). Other measures of motor cortical (motor threshold, cortical silent period duration), spinal (peripheral silent period duration, F-wave) and neuromuscular excitability (maximum M-wave) remained unchanged. This shift in the balance from excitation to inhibition may assist, by improving the 'signal-to-noise ratio' in motor cortex, in the positive modulating effect of cabergoline on practice-dependent plasticity.

Speech and nonspeech sequence skill learning in adults who stutter

Two studies compared the speech and nonspeech sequence skill learning of nine persons who stutter (PWS) and nine matched fluent speakers (PNS). Sequence skill learning was defined as a continuing process of stable improvement in speed and/or accuracy of sequencing performance over practice and was measured by comparing PWS's and PNS's performance curves of accuracy, reaction time, and sequence duration, as well as retention and transfer. In experiment one, participants completed a 30-trial finger tapping sequence and in experiment two, a 30-trial read-aloud sequence of nonsense syllables. Significant between-group differences were found in the speed of sequencing performance after practice, and on retention and transfer tests. These results partially supported the inference that PWS demonstrated differences in early stages of sequence skill learning compared to PNS.

EDUCATIONAL OBJECTIVES

As a result of this activity the participant will be able to: (1) define skill learning and the important indicators of skill learning; (2) summarize the reviewed literature concerning the performance of PWS on speech and nonspeech sequencing tasks over practice; and (3) explain the implication of reaction time differences over practice between PWS and PNS.

Learning and retention of movement sequences in Parkinson's disease

The purpose of this study was to examine motor learning and retention given extensive practice in two fundamentally different movement sequences. One sequence was a memory-driven task (performing a series of whole body positions from memory) and the other a context-driven task (buttoning). Practice took place over 3 weeks, with performance measured weekly; retention was measured weekly for 3 weeks after practice. There were 7 people with Parkinson's disease (PD) and 7 age-matched neurologically healthy people who participated in this study. Both groups improved performance on both tasks with practice, with the majority of the change for the PD group occurring between 1 and 2 weeks of practice. Although those with PD did not necessarily perform as well as age-matched controls, they learned both sequences in a manner similar to age-matched controls, and exhibited retention across the 3-week retention interval. If people with PD are given sufficient practice they can learn and retain both memory-based and context-driven movement sequences as well as age-matched controls. The results provide support for maintaining physical activity and for intervention through movement therapy.

The transition to increased automaticity during finger sequence learning in adult males who stutter

The present study compared the automaticity levels of persons who stutter (PWS) and persons who do not stutter (PNS) on a practiced finger sequencing task under dual task conditions. Automaticity was defined as the amount of attention required for task performance. Twelve PWS and 12 control subjects practiced finger tapping sequences under single and then dual task conditions. Control subjects performed the sequencing task significantly faster and less variably under single versus dual task conditions while PWS' performance was consistently slow and variable (comparable to the dual task performance of control subjects) under both conditions. Control subjects were significantly more accurate on a colour recognition distracter task than PWS under dual task conditions. These results suggested that control subjects transitioned to quick, accurate and increasingly automatic performance on the sequencing task after practice, while PWS did not. Because most stuttering treatment programs for adults include practice and automatization of new motor speech skills, findings of this finger sequencing study and future studies of speech sequence learning may have important implications for how to maximize stuttering treatment effectiveness.

EDUCATIONAL OBJECTIVES

As a result of this activity, the participant will be able to: (1) Define automaticity and explain the importance of dual task paradigms to investigate automaticity; (2) Relate the proposed relationship between motor learning and automaticity as stated by the authors; (3) Summarize the reviewed literature concerning the performance of PWS on dual tasks; and (4) Explain why the ability to transition to automaticity during motor learning may have important clinical implications for stuttering treatment effectiveness.

Learning a high-precision locomotor task in patients with Parkinson's disease

We evaluated the acquisition and performance of a high-precision locomotor task in patients with Parkinson's disease (PD) and healthy subjects. All subjects walked on a treadmill and had to step repetitively as low as possible over an obstacle without touching it. During blocks 1 and 2, the subjects had full vision and received additional acoustic warning and feedback signals. During block 3, vision became restricted. Changes in foot clearance and the number of obstacle hits were evaluated. Initially, PD patients performed poorer and improved foot clearance slower. After task repetition, the groups performed similarly. Restricting vision deteriorated performance in both groups. The similar performance of PD patients after task repetition might indicate that adequate training could improve adaptive locomotor behavior in PD patients.

Altered plasticity of the human motor cortex in Parkinson's disease

Interventional paired associative stimulation (IPAS) to the contralateral peripheral nerve and cerebral cortex can enhance the primary motor cortex (M1) excitability with two synchronously arriving inputs. This study investigated whether dopamine contributed to the associative long-term potentiation-like effect in the M1 in Parkinson's disease (PD) patients. Eighteen right-handed PD patients and 11 right-handed age-matched healthy volunteers were studied. All patients were studied after 12 hours off medication with levodopa replacement (PD-off). Ten patients were also evaluated after medication (PD-on). The IPAS comprised a single electric stimulus to the right median nerve at the wrist and subsequent transcranial magnetic stimulation of the left M1 with an interstimulus interval of 25 milliseconds (240 paired stimuli every 5 seconds for 20 minutes). The motor-evoked potential amplitude in the right abductor pollicis brevis muscle was increased by IPAS in healthy volunteers, but not in PD patients. IPAS did not affect the motor-evoked potential amplitude in the left abductor pollicis brevis. The ratio of the motor-evoked potential amplitude before and after IPAS in PD-off patients increased after dopamine replacement. Thus, dopamine might modulate cortical plasticity in the human M1, which could be related to higher order motor control, including motor learning.