Basal ganglia contribution to the initiation of corrective submovements

Role of the Cerebellum in the Construction of Functional and Geometrical Spaces

The perceptual and motor systems appear to have a set of movement primitives that exhibit certain geometric and kinematic invariances. Complex patterns and mental representations can be produced by (re)combining some simple motor elements in various ways using basic operations, transformations, and respecting a set of laws referred to as kinematic laws of motion. For example, point-to-point hand movements are characterized by straight hand paths with single-peaked-bell-shaped velocity profiles, whereas hand speed profiles for curved trajectories are often irregular and more variable, with speed valleys and inflections extrema occurring at the peak curvature. Curvature and speed are generically related by the 2/3 power law. Mathematically, such laws can be deduced from a combination of Euclidean, affine, and equi-affine geometries, whose neural correlates have been partially detected in various brain areas including the cerebellum and the basal ganglia. The cerebellum has been found to play an important role in the control of coordination, balance, posture, and timing over the past years. It is also assumed that the cerebellum computes forward internal models in relationship with specific cortical and subcortical brain regions but its motor relationship with the perceptual space is unclear. A renewed interest in the geometrical and spatial role of the cerebellum may enable a better understanding of its specific contribution to the action-perception loop and behavior's adaptation. In this sense, we complete this overview with an innovative theoretical framework that describes a possible implementation and selection by the cerebellum of geometries adhering to different mathematical laws.

Distinct neural representations during a brain-machine interface and manual reaching task in motor cortex, prefrontal cortex, and striatum

Although brain-machine interfaces (BMIs) are directly controlled by the modulation of a select local population of neurons, distributed networks consisting of cortical and subcortical areas have been implicated in learning and maintaining control. Previous work in rodents has demonstrated the involvement of the striatum in BMI learning. However, the prefrontal cortex has been largely ignored when studying motor BMI control despite its role in action planning, action selection, and learning abstract tasks. Here, we compare local field potentials simultaneously recorded from primary motor cortex (M1), dorsolateral prefrontal cortex (DLPFC), and the caudate nucleus of the striatum (Cd) while nonhuman primates perform a two-dimensional, self-initiated, center-out task under BMI control and manual control. Our results demonstrate the presence of distinct neural representations for BMI and manual control in M1, DLPFC, and Cd. We find that neural activity from DLPFC and M1 best distinguishes control types at the go cue and target acquisition, respectively, while M1 best predicts target-direction at both task events. We also find effective connectivity from DLPFC → M1 throughout both control types and Cd → M1 during BMI control. These results suggest distributed network activity between M1, DLPFC, and Cd during BMI control that is similar yet distinct from manual control.

Age-related decline of online visuomotor adaptation: a combined effect of deteriorations of motor anticipation and execution

The literature has established that the capability of visuomotor adaptation decreases with aging. However, the underlying mechanisms of this decline are yet to be fully understood. The current study addressed this issue by examining how aging affected visuomotor adaptation in a continuous manual tracking task with delayed visual feedback. To distinguish separate contributions of the declined capability of motor anticipation and deterioration of motor execution to this age-related decline, we recorded and analyzed participants' manual tracking performances and their eye movements during tracking. Twenty-nine older people and twenty-three young adults (control group) participated in this experiment. The results showed that the age-related decline of visuomotor adaptation was strongly linked to degraded performance in predictive pursuit eye movement, indicating that declined capability motor anticipation with aging had critical influences on the age-related decline of visuomotor adaptation. Additionally, deterioration of motor execution, measured by random error after controlling for the lag between target and cursor, was found to have an independent contribution to the decline of visuomotor adaptation. Taking these findings together, we see a picture that the age-related decline of visuomotor adaptation is a joint effect of the declined capability of motor anticipation and the deterioration of motor execution with aging.

Distinct neural representations during a brain-machine interface and manual reaching task in motor cortex, prefrontal cortex, and striatum

Although brain-machine interfaces (BMIs) are directly controlled by the modulation of a select local population of neurons, distributed networks consisting of cortical and subcortical areas have been implicated in learning and maintaining control. Previous work in rodent BMI has demonstrated the involvement of the striatum in BMI learning. However, the prefrontal cortex has been largely ignored when studying motor BMI control despite its role in action planning, action selection, and learning abstract tasks. Here, we compare local field potentials simultaneously recorded from the primary motor cortex (M1), dorsolateral prefrontal cortex (DLPFC), and the caudate nucleus of the striatum (Cd) while nonhuman primates perform a two-dimensional, self-initiated, center-out task under BMI control and manual control. Our results demonstrate the presence of distinct neural representations for BMI and manual control in M1, DLPFC, and Cd. We find that neural activity from DLPFC and M1 best distinguish between control types at the go cue and target acquisition, respectively. We also found effective connectivity from DLPFC→M1 throughout trials across both control types and Cd→M1 during BMI control. These results suggest distributed network activity between M1, DLPFC, and Cd during BMI control that is similar yet distinct from manual control.

Decision heuristics in contexts integrating action selection and execution

Heuristics can inform human decision making in complex environments through a reduction of computational requirements (accuracy-resource trade-off) and a robustness to overparameterisation (less-is-more). However, tasks capturing the efficiency of heuristics typically ignore action proficiency in determining rewards. The requisite movement parameterisation in sensorimotor control questions whether heuristics preserve efficiency when actions are nontrivial. We developed a novel action selection-execution task requiring joint optimisation of action selection and spatio-temporal skillful execution. State-appropriate choices could be determined by a simple spatial heuristic, or by more complex planning. Computational models of action selection parsimoniously distinguished human participants who adopted the heuristic from those using a more complex planning strategy. Broader comparative analyses then revealed that participants using the heuristic showed combined decisional (selection) and skill (execution) advantages, consistent with a less-is-more framework. In addition, the skill advantage of the heuristic group was predominantly in the core spatial features that also shaped their decision policy, evidence that the dimensions of information guiding action selection might be yoked to salient features in skill learning.

When intercepting moving targets, mid-movement error corrections reflect distinct responses to visual and haptic perturbations

We examined a key aspect of sensorimotor skill: the capability to correct performance errors that arise mid-movement. Participants grasped the handle of a robot that imposed a nominal viscous resistance to hand movement. They watched a target move pseudo-randomly just above the horizontal plane of hand motion and initiated quick interception movements when cued. On some trials, the robot's viscosity or the target's speed changed without warning coincident with the GO cue. We fit a sum-of-Gaussians model to mechanical power measured at the handle to determine the number, magnitude, and relative timing of submovements occurring in each interception attempt. When a single submovement successfully intercepted the target, capture times averaged 410 ms. Sometimes, two or more submovements were required. Initial error corrections typically occurred before feedback could indicate the target had been captured or missed. Error corrections occurred sooner after movement onset in response to mechanical viscosity increases (at 154 ms) than to unprovoked errors on control trials (215 ms). Corrections occurred later (272 ms) in response to viscosity decreases. The latency of corrections for target speed changes did not differ from those in control trials. Remarkably, these early error corrections accommodated the altered testing conditions; speed/viscosity increases elicited more vigorous corrections than in control trials with unprovoked errors; speed/viscosity decreases elicited less vigorous corrections. These results suggest that the brain monitors and predicts the outcome of evolving movements, rapidly infers causes of mid-movement errors, and plans and executes corrections-all within 300 ms of movement onset.

An fMRI meta-analysis of the role of the striatum in everyday-life vs laboratory-developed habits

The dorsolateral striatum plays a critical role in the acquisition and expression of stimulus-response habits that are learned in experimental laboratories. Here, we use meta-analytic procedures to contrast the neural circuits activated by laboratory-acquired habits with those activated by stimulus-response behaviours acquired in everyday-life. We confirmed that newly learned habits rely more on the anterior putamen with activation extending into caudate and nucleus accumbens. Motor and associative components of everyday-life habits were identified. We found that motor-dominant stimulus-response associations developed outside the laboratory primarily engaged posterior dorsal putamen, supplementary motor area (SMA) and cerebellum. Importantly, associative components were also represented in the posterior putamen. Thus, common neural representations for both naturalistic and laboratory-based habits were found in the left posterior and right anterior putamen. These findings suggest a partial common striatal substrate for habitual actions that are performed predominantly by stimulus-response associations represented in the posterior striatum. The overlapping neural substrates for laboratory and everyday-life habits supports the use of both methods for the analysis of habitual behaviour.

Reaching and Grasping Movements in Parkinson's Disease: A Review

Parkinson's disease (PD) is known to affect the brain motor circuits involving the basal ganglia (BG) and to induce, among other signs, general slowness and paucity of movements. In upper limb movements, PD patients show a systematic prolongation of movement duration while maintaining a sufficient level of endpoint accuracy. PD appears to cause impairments not only in movement execution, but also in movement initiation and planning, as revealed by abnormal preparatory activity of motor-related brain areas. Grasping movement is affected as well, particularly in the coordination of the hand aperture with the transport phase. In the last fifty years, numerous behavioral studies attempted to clarify the mechanisms underlying these anomalies, speculating on the plausible role that the BG-thalamo-cortical circuitry may play in normal and pathological motor control. Still, many questions remain open, especially concerning the management of the speed-accuracy tradeoff and the online feedback control. In this review, we summarize the literature results on reaching and grasping in parkinsonian patients. We analyze the relevant hypotheses on the origins of dysfunction, by focusing on the motor control aspects involved in the different movement phases and the corresponding role played by the BG. We conclude with an insight into the innovative stimulation techniques and computational models recently proposed, which might be helpful in further clarifying the mechanisms through which PD affects reaching and grasping movements.

Articulatory Gain Predicts Motor Cortex and Subthalamic Nucleus Activity During Speech

Speaking precisely is important for effective verbal communication, and articulatory gain is one component of speech motor control that contributes to achieving this goal. Given that the basal ganglia have been proposed to regulate the speed and size of limb movement, that is, movement gain, we explored the basal ganglia contribution to articulatory gain, through local field potentials (LFP) recorded simultaneously from the subthalamic nucleus (STN), precentral gyrus, and postcentral gyrus. During STN deep brain stimulation implantation for Parkinson's disease, participants read aloud consonant-vowel-consonant syllables. Articulatory gain was indirectly assessed using the F2 Ratio, an acoustic measurement of the second formant frequency of/i/vowels divided by/u/vowels. Mixed effects models demonstrated that the F2 Ratio correlated with alpha and theta activity in the precentral gyrus and STN. No correlations were observed for the postcentral gyrus. Functional connectivity analysis revealed that higher phase locking values for beta activity between the STN and precentral gyrus were correlated with lower F2 Ratios, suggesting that higher beta synchrony impairs articulatory precision. Effects were not related to disease severity. These data suggest that articulatory gain is encoded within the basal ganglia-cortical loop.

Grasping and Manipulation: Neural Bases and Anatomical Circuitry in Humans

Neurophysiological and neuroimaging evidence suggests a significant contribution of several brain areas, including subdivisions of the parietal and the premotor cortex, during the processing of different components of hand and arm movements. Many investigations improved our knowledge about the neural processes underlying the execution of reaching and grasping actions, while few studies have directly investigated object manipulation. Most studies on the latter topic concern the use of tools to achieve specific goals. Yet, there are very few studies on pure manipulation performed in order to explore and recognize objects, as well as on manipulation performed with a high level of manual dexterity. Another dimension that is quite neglected by the available studies on grasping and manipulation is, on the one hand, the contribution of the subcortical nodes, first of all the basal ganglia and cerebellum, to these functions, and, on the other hand, recurrent connections of these structures with cortical areas. In the first part, we have reviewed the parieto-premotor and subcortical circuits underlying reaching and grasping in humans, with a focus on functional neuroimaging data. Then, we have described the main structures recruited during object manipulation. We have also reported the contribution of recent structural connectivity techniques whereby the cortico-cortical and cortico-subcortical connections of grasping-related and manipulation-related areas in the human brain can be determined. Based on our review, we have concluded that studies on cortical and subcortical circuits involved in grasping and manipulation might be promising to provide new insights about motor learning and brain plasticity in patients with motor disorders.

Variability of Voluntary Cough Airflow in Healthy Adults and Parkinson's Disease

Cough is an important airway protective behavior responsible for ejecting material from the airway to prevent pneumonia, a leading cause of death in older adults and individuals with Parkinson's disease (PD). Variability of motor performance for both spinal and bulbar functions has been documented; however, there are no studies examining variability of cough motor control in PD and healthy controls. The present study examined the effects of age and PD on variability of voluntary cough performance. Twenty-five healthy younger adults (HYA), 26 healthy older adults (HOA), and 16 participants with PD completed three trials of sequential voluntary cough with spirometry. Coefficients of variation were used to examine variability between groups. Increased variability of cough expired volume (p = 0.012) and inspiratory volume (p = 0.006) was appreciated in HOAs compared to HYAs. Participants with PD demonstrated increased variability of cough expired volume (p = 0.029), peak expiratory flow rise time (p = 0.016), and cough volume acceleration (p = 0.034) compared to HOAs. Though participants with PD descriptively demonstrated increased peak expiratory flow rate compared to HOAs, this finding was statistically nonsignificant after adjusting for multiple comparisons (p = 0.072). This study identified that variability in cough airflow increases in healthy aging and Parkinson's disease. These motor control impairments may be attributed to age and disease-related sensorimotor changes in the peripheral and central nervous system. Future research will be necessary to examine the relationship between inconsistent cough motor output, airway invasion, and aspiration pneumonia in PD.

Automatic Online Motor Control Is Intact in Parkinson's Disease With and Without Perceptual Awareness

In the double-step paradigm, healthy human participants automatically correct reaching movements when targets are displaced. Motor deficits are prominent in Parkinson's disease (PD) patients. In the lone investigation of online motor correction in PD using the double-step task, a recent study found that PD patients performed unconscious adjustments appropriately but seemed impaired for consciously-perceived modifications. Conscious perception of target movement was achieved by linking displacement to movement onset. PD-related bradykinesia disproportionately prolonged preparatory phases for movements to original target locations for patients, potentially accounting for deficits. Eliminating this confound in a double-step task, we evaluated the effect of conscious awareness of trajectory change on online motor corrections in PD. On and off dopaminergic therapy, PD patients (n = 14) and healthy controls (n = 14) reached to peripheral visual targets that remained stationary or unexpectedly moved during an initial saccade. Saccade latencies in PD are comparable to controls'. Hence, target displacements occurred at equal times across groups. Target jump size affected conscious awareness, confirmed in an independent target displacement judgment task. Small jumps were subliminal, but large target displacements were consciously perceived. Contrary to the previous result, PD patients performed online motor corrections normally and automatically, irrespective of conscious perception. Patients evidenced equivalent movement durations for jump and stay trials, and trajectories for patients and controls were identical, irrespective of conscious perception. Dopaminergic therapy had no effect on performance. In summary, online motor control is intact in PD, unaffected by conscious perceptual awareness. The basal ganglia are not implicated in online corrective responses.

Altered Functional Connectivity of Striatal Subregions in Patients with Multiple Sclerosis

Abnormal corticostriatal resting-state functional connectivity (rsFC) has been implicated in the neuropathology of multiple sclerosis. The striatum, a component of the basal ganglia, is involved in diverse functions including movement, cognition, emotion, and limbic information processing. However, the brain circuits of the striatal subregions contributing to the changes in rsFC in relapsing–remitting multiple sclerosis (RRMS) patients remain unknown. We used six subdivisions of the striatum in each hemisphere as seeds to investigate the rsFC of striatal subregions between RRMS patients and matched healthy controls (HCs). In addition, we also scanned a subcohort of RRMS patients after an average of 7 months to test the reliability of our findings. Compared to HCs, we found significantly increased dorsal caudal putamen (DCP) connectivity with the premotor area, dorsal lateral prefrontal cortex (DLPFC), insula, precuneus, and superior parietal lobule, and significantly increased connectivity between the superior ventral striatum and posterior cingulate cortex (PCC) in RRMS patients following both scans. Furthermore, we found significant associations between the Expanded Disability Status Scale and the rsFC of the left DCP with the DLPFC and parietal areas in RRMS patients. Our results suggest that the DCP may be a critical striatal subregion in the pathophysiology of RRMS.

The Use of Open- and Closed-Loop Control During Goal-Directed Force Responses by Children with Heavy Prenatal Alcohol Exposure

BACKGROUND

Many daily functional activities involve goal-directed responses based on open-loop and closed-loop motor control, yet little is known about how children with heavy prenatal alcohol exposure organize and regulate these 2 types of control systems when completing a goal-directed force response.

METHODS

Children with (n = 19) or without (n = 23) heavy prenatal alcohol exposure were required to match a target force (25 and 50% of maximum voluntary force) in a specified target time (200, 800, and 2,000 ms). Target force and produced force were visually displayed on a computer monitor. The analog force-time record was parsed into 2 segments: the period beginning from force initiation to the first reversal in force was designated the open-loop phase, and the remainder of the response was the closed-loop phase.

RESULTS

Compared to controls, alcohol-exposed children produced a significantly shorter duration of open-loop control, a higher open-loop phase rate of force development, a shorter time to reach maximum force during the closed-loop phase, and greater absolute target force error. Increasing target force magnitude did not differentially alter the performance of the clinical group.

CONCLUSIONS

The results indicate that alcohol-exposed children experience deficits in completing goal-directed force responses that likely stem from an alcohol-related insult to the central nervous system. Therapeutic exercises should be designed to recalibrate internal timing systems and improve visuomotor integration.

Impact of Parkinson's disease on proprioceptively based on-line movement control

Evidence suggests that Parkinson's disease (PD) patients produce large spatial errors when reaching to proprioceptively defined targets. Here, we examined whether these movement inaccuracies result mainly from impaired use of proprioceptive inputs for movement planning mechanisms or from on-line movement guidance. Medicated and non-medicated PD patients and healthy controls performed three-dimensional reaching movements in four sensorimotor conditions that increase proprioceptive processing requirements. We assessed the influence of these sensorimotor conditions on the final accuracy and initial kinematics of the movements. If the patterns of final errors are primarily determined by planning processes before the initiation of the movement, the initial kinematics of reaching movements should show similar trends and predict the pattern of final errors. Medicated and non-medicated PD patients showed a greater mean level of final 3D errors than healthy controls when proprioception was the sole source of information guiding the movement, but this difference reached significance only for medicated PD patients. However, the pattern of initial kinematics and final spatial errors were markedly different both between sensorimotor conditions and between groups. Furthermore, medicated and non-medicated PD patients were less efficient than healthy controls in compensating for their initial spatial errors (hand distance from target location at peak velocity) when aiming at proprioceptively defined compared to visually defined targets. Considered together, the results are consistent with a selective deficit in proprioceptively based movement guidance in PD. Furthermore, dopaminergic medication did not improve proprioceptively guided movements in PD patients, indicating that dopaminergic dysfunction within the basal ganglia is not solely responsible for these deficits.

The role of prediction and outcomes in adaptive cognitive control

Humans adaptively perform actions to achieve their goals. This flexible behaviour requires two core abilities: the ability to anticipate the outcomes of candidate actions and the ability to select and implement actions in a goal-directed manner. The ability to predict outcomes has been extensively researched in reinforcement learning paradigms, but this work has often focused on simple actions that are not embedded in hierarchical and sequential structures that are characteristic of goal-directed human behaviour. On the other hand, the ability to select actions in accordance with high-level task goals, particularly in the presence of alternative responses and salient distractors, has been widely researched in cognitive control paradigms. Cognitive control research, however, has often paid less attention to the role of action outcomes. The present review attempts to bridge these accounts by proposing an outcome-guided mechanism for selection of extended actions. Our proposal builds on constructs from the hierarchical reinforcement learning literature, which emphasises the concept of reaching and evaluating informative states, i.e., states that constitute subgoals in complex actions. We develop an account of the neural mechanisms that allow outcome-guided action selection to be achieved in a network that relies on projections from cortical areas to the basal ganglia and back-projections from the basal ganglia to the cortex. These cortico-basal ganglia-thalamo-cortical 'loops' allow convergence - and thus integration - of information from non-adjacent cortical areas (for example between sensory and motor representations). This integration is essential in action sequences, for which achieving an anticipated sensory state signals the successful completion of an action. We further describe how projection pathways within the basal ganglia allow selection between representations, which may pertain to movements, actions, or extended action plans. The model lastly envisages a role for hierarchical projections from the striatum to dopaminergic midbrain areas that enable more rostral frontal areas to bias the selection of inputs from more posterior frontal areas via their respective representations in the basal ganglia.

Higher landing accuracy in expert pilots is associated with lower activity in the caudate nucleus

The most common lethal accidents in General Aviation are caused by improperly executed landing approaches in which a pilot descends below the minimum safe altitude without proper visual references. To understand how expertise might reduce such erroneous decision-making, we examined relevant neural processes in pilots performing a simulated landing approach inside a functional MRI scanner. Pilots (aged 20-66) were asked to "fly" a series of simulated "cockpit view" instrument landing scenarios in an MRI scanner. The scenarios were either high risk (heavy fog-legally unsafe to land) or low risk (medium fog-legally safe to land). Pilots with one of two levels of expertise participated: Moderate Expertise (Instrument Flight Rules pilots, n = 8) or High Expertise (Certified Instrument Flight Instructors or Air-Transport Pilots, n = 12). High Expertise pilots were more accurate than Moderate Expertise pilots in making a "land" versus "do not land" decision (CFII: d' = 3.62 ± 2.52; IFR: d' = 0.98 ± 1.04; p<.01). Brain activity in bilateral caudate nucleus was examined for main effects of expertise during a "land" versus "do not land" decision with the no-decision control condition modeled as baseline. In making landing decisions, High Expertise pilots showed lower activation in the bilateral caudate nucleus (0.97 ± 0.80) compared to Moderate Expertise pilots (1.91 ± 1.16) (p<.05). These findings provide evidence for increased "neural efficiency" in High Expertise pilots relative to Moderate Expertise pilots. During an instrument approach the pilot is engaged in detailed examination of flight instruments while monitoring certain visual references for making landing decisions. The caudate nucleus regulates saccade eye control of gaze, the brain area where the "expertise" effect was observed. These data provide evidence that performing "real world" aviation tasks in an fMRI provide objective data regarding the relative expertise of pilots and brain regions involved in it.

Neural correlates of progressive reduction of bradykinesia in de novo Parkinson's disease

BACKGROUND

A progressive reduction in the speed and amplitude of repetitive action is an essential component of bradykinesia, which is called sequence effect (SE). Because SE is specific to Parkinson's disease (PD) and is suggested to be associated with motor arrest, its features are of great interest. The aim of this study was, for the first time, to find the neural correlates of SE and to demonstrate whether dopaminergic deficit is correlated with SE.

METHODS

We enrolled 12 patients with de novo PD at a tertiary referral hospital. Correlations between SE severity and alterations in gray and white matter were studied. The association between severity of the SE and striatal dopaminergic deficits was also analyzed.

RESULTS

There was a significant negative correlation between the volumetric changes in the anterior cingulate cortex (ACC) and the inferior semilunar lobule of the cerebellum and the degree of SE. There was a significant correlation between the long association fibers (the superior longitudinal fasciculus, the uncinate fasciculus, and the inferior fronto-occipital fasciculus) connecting the frontal lobes to the temporal, parietal, and occipital lobes and SE. There was a significant negative correlation between SE in the more affected hand and the caudate dopamine transporter binding in the more affected hemisphere.

CONCLUSIONS

Our results suggest that the ACC and the cerebellum (inferior semilunar lobule) are associated with the severity of SE. Taken together with DTI findings, the present study proposes that ACC may have an important role. Our data show that the caudate dopaminergic activity may be related to SE.

Spatiotemporal dynamics of online motor correction processing revealed by high-density electroencephalography

The ability to control online motor corrections is key to dealing with unexpected changes arising in the environment with which we interact. How the CNS controls online motor corrections is poorly understood, but evidence has accumulated in favor of a submovement-based model in which apparently continuous movement is segmented into distinct submovements. Although most studies have focused on submovements' kinematic features, direct links with the underlying neural dynamics have not been extensively explored. This study sought to identify an electroencephalographic signature of submovements. We elicited kinematic submovements using a double-step displacement paradigm. Participants moved their wrist toward a target whose direction could shift mid-movement with a 50% probability. Movement kinematics and cortical activity were concurrently recorded with a low-friction robotic device and high-density electroencephalography. Analysis of spatiotemporal dynamics of brain activation and its correlation with movement kinematics showed that the production of each kinematic submovement was accompanied by (1) stereotyped topographic scalp maps and (2) frontoparietal ERPs time-locked to submovements. Positive ERP peaks from frontocentral areas contralateral to the moving wrist preceded kinematic submovement peaks by 220-250 msec and were followed by positive ERP peaks from contralateral parietal areas (140-250 msec latency, 0-80 msec before submovement peaks). Moreover, individual subject variability in the latency of frontoparietal ERP components following the target shift significantly predicted variability in the latency of the corrective submovement. Our results are in concordance with evidence for the intermittent nature of continuous movement and elucidate the timing and role of frontoparietal activations in the generation and control of corrective submovements.

Characterizing and predicting submovements during human three-dimensional arm reaches

We have demonstrated that 3D target-oriented human arm reaches can be represented as linear combinations of discrete submovements, where the submovements are a set of minimum-jerk basis functions for the reaches. We have also demonstrated the ability of deterministic feed-forward Artificial Neural Networks (ANNs) to predict the parameters of the submovements. ANNs were trained using kinematic data obtained experimentally from five human participants making target-directed movements that were decomposed offline into minimum-jerk submovements using an optimization algorithm. Under cross-validation, the ANNs were able to accurately predict the parameters (initiation-time, amplitude, and duration) of the individual submovements. We also demonstrated that the ANNs can together form a closed-loop model of human reaching capable of predicting 3D trajectories with VAF >95.9% and RMSE ≤4.32 cm relative to the actual recorded trajectories. This closed-loop model is a step towards a practical arm trajectory generator based on submovements, and should be useful for the development of future arm prosthetic devices that are controlled by brain computer interfaces or other user interfaces.

Aging associated changes in the motor control of ankle movements in the brain

Although age-related gait changes have been well characterized, little is known regarding potential functional changes in central motor control of distal lower limb movements with age. We hypothesized that there are age-related changes in brain activity associated with the control of repetitive ankle movements, an element of gait feasible for study with functional magnetic resonance imaging. We analyzed standardized functional magnetic resonance imaging data from 102 right-foot dominant healthy participants aged 20-83 years for age-associated effects using FSL and a meta-analysis using coordinate-based activation likelihood estimation. For the first time, we have confirmed age-related changes in brain activity with this gait-related movement of the lower limb in a large population. Increasing age correlated strongly with increased movement-associated activity in the cerebellum and precuneus. Given that task performance did not vary with age, we interpret these changes as potentially compensatory for other age-related changes in the sensorimotor network responsible for control of limb function.

Automatic online control of motor adjustments in reaching and grasping

Following the princeps investigations of Marc Jeannerod on action-perception, specifically, goal-directed movement, this review article addresses visual and non-visual processes involved in guiding the hand in reaching or grasping tasks. The contributions of different sources of correction of ongoing movements are considered; these include visual feedback of the hand, as well as the often-neglected but important spatial updating and sharpening of goal localization following gaze-saccade orientation. The existence of an automatic online process guiding limb trajectory toward its goal is highlighted by a series of princeps experiments of goal-directed pointing movements. We then review psychophysical, electrophysiological, neuroimaging and clinical studies that have explored the properties of these automatic corrective mechanisms and their neural bases, and established their generality. Finally, the functional significance of automatic corrective mechanisms-referred to as motor flexibility-and their potential use in rehabilitation are discussed.

Age- and gender-related metabonomic alterations in striatum and cerebellar cortex in rats

In order to identify the neurochemical alterations in motor associated subcortical nuclei, and enhance our understanding of neurophysiology of progressive reduction in fine motor control with aging, the metabolic changes in striatum and cerebellar cortex in SD rats along with aging were investigated using a metabonomic approach based on high resolution "magic angle spinning" 1H-NMR spectroscopy and partial least squares-discriminant analysis. It was found that there were increased myo-inositol and lactate, and decreased taurine in these two brain regions of old rats. The above changes may be a marker for alterations of neuronal cells, which reduce fine motor control. Besides, some of the metabolites are gender-related and region-specific. Old female rats had decreased glutamate and increased creatine in striatum, while old male rats had increased choline in striatum, and increased GABA in cerebellar cortex, respectively. However, further analyses showed that most of the metabolites in male rats were not distinctively different with those of female ones except choline, which was in a relative lower level in striatum of male rats. All this results suggest that energy metabolism is an important indication of age-related change, which is not only in male, but also in female rats.

Involvement of human internal globus pallidus in the early modulation of cortical error-related activity

The detection and assessment of errors are a prerequisite to adapt behavior and improve future performance. Error monitoring is afforded by the interplay between cortical and subcortical neural systems. Ample evidence has pointed to a specific cortical error-related evoked potential, the error-related negativity (ERN), during the detection and evaluation of response errors. Recent models of reinforcement learning implicate the basal ganglia (BG) in early error detection following the learning of stimulus-response associations and in the modulation of the cortical ERN. To investigate the influence of the human BG motor output activity on the cortical ERN during response errors, we recorded local field potentials from the sensorimotor area of the internal globus pallidus and scalp electroencephalogram representing activity from the posterior medial frontal cortex in patients with idiopathic dystonia (hands not affected) during a flanker task. In error trials, a specific pallidal error-related potential arose 60 ms prior to the cortical ERN. The error-related changes in pallidal activity-characterized by theta oscillations-were predictive of the cortical error-related activity as assessed by Granger causality analysis. Our findings show an early modulation of error-related activity in the human pallidum, suggesting that pallidal output influences the cortex at an early stage of error detection.

Brain activity in adults who stutter: similarities across speaking tasks and correlations with stuttering frequency and speaking rate

Many differences in brain activity have been reported between persons who stutter (PWS) and typically fluent controls during oral reading tasks. An earlier meta-analysis of imaging studies identified stutter-related regions, but recent studies report less agreement with those regions. A PET study on adult dextral PWS (n=18) and matched fluent controls (CONT, n=12) is reported that used both oral reading and monologue tasks. After correcting for speech rate differences between the groups the task-activation differences were surprisingly small. For both analyses only some regions previously considered stutter-related were more activated in the PWS group than in the CONT group, and these were also activated during eyes-closed rest (ECR). In the PWS group, stuttering frequency was correlated with cortico-striatal-thalamic circuit activity in both speaking tasks. The neuroimaging findings for the PWS group, relative to the CONT group, appear consistent with neuroanatomic abnormalities being increasingly reported among PWS.

The centre of the brain: topographical model of motor, cognitive, affective, and somatosensory functions of the basal ganglia

The basal ganglia have traditionally been viewed as motor processing nuclei; however, functional neuroimaging evidence has implicated these structures in more complex cognitive and affective processes that are fundamental for a range of human activities. Using quantitative meta-analysis methods we assessed the functional subdivisions of basal ganglia nuclei in relation to motor (body and eye movements), cognitive (working-memory and executive), affective (emotion and reward) and somatosensory functions in healthy participants. We document affective processes in the anterior parts of the caudate head with the most overlap within the left hemisphere. Cognitive processes showed the most widespread response, whereas motor processes occupied more central structures. On the basis of these demonstrated functional roles of the basal ganglia, we provide a new comprehensive topographical model of these nuclei and insight into how they are linked to a wide range of behaviors.

Mechanisms of neural reorganization in chronic stroke subjects after virtual reality training

This study investigates patterns of brain reorganization in chronic stroke subjects after two weeks of robot-assisted arm and hand training in virtual reality (VR). Four subjects were studied with event-related fMRI while doing simple paretic hand finger movements before (double baseline) and after training. Bilateral hand movements were recorded and used to provide real-time feedback to subjects during scanning to eliminate performance confounds on fMRI results. The kinematic parameters of each movement were also used in the general linear model with the BOLD signal to investigate training-induced changes in neuromotor coupling. Univariate analysis showed an increase in BOLD signal in the ipsilesional hemisphere in two subjects and a decrease in activity in the other two subjects. Seed voxel based functional connectivity analysis revealed an increase in connectivity between ipsilesional motor cortex and bilateral sensorimotor cortex during finger movements in all four subjects. Hemispheric laterality index values showed a tendency to decrease reflecting a reduction in the over-dominance of the contralesional hemisphere. The study is novel in terms of 1) tracking finger movement during a motor task in the scanner, 2) monitoring motor performance during the experiment and 3) giving online visual feedback of subjects' movement. This pilot study introduces a novel approach to study neural plasticity by combining measures of regional intensity, interregional interactions (using functional connectivity analysis and hemispheric laterality index), and modulation in the strength of neuromotor coupling.

A longitudinal study of motor performance and striatal [18F]fluorodopa uptake in Parkinson's disease

Although [(18)F]fluoro-L: -dopa [FDOPA] positron emission tomography (PET) has been used as a surrogate outcome measure in Parkinson's disease therapeutic trials, this biomarker has not been proven to reflect clinical status longitudinally. We completed a retrospective analysis of relationships between computerized sampling of motor performance, FDOPA PET, and clinical outcome scales, repeated over 4 years, in 26 Parkinson's disease (PD) patients and 11 healthy controls. Mixed effects analyses showed that movement time and tongue strength best differentiated PD from control subjects. In the treated PD cohort, motor performance measures changed gradually in contrast to a steady decline in striatal FDOPA uptake. Prolonged reaction and movement time were related to lower caudate nucleus FDOPA uptake, and abnormalities in hand fine force control were related to mean striatal FDOPA uptake. These findings provide evidence that regional loss of nigrostriatal inputs to frontostriatal networks affects specific aspects of motor function.

Neural processes of preparatory control for stop signal inhibition

This study investigated the preparatory control of motor inhibition and motor execution using a stop signal task (SST) and functional magnetic resonance imaging (fMRI). In the SST, a frequent "go" signal triggered a prepotent response and a less frequent "stop" signal prompted the inhibition of this response. Preparatory control of motor inhibition and execution in the stop signal trials were examined by contrasting brain activation between stop success and stop error trials during the fore-period, in which participants prepared to respond to go or to stop. Results from 91 healthy adults showed greater activation in the right prefrontal cortex and inferior parietal lobule during preparatory motor inhibition. Preparatory motor execution activated bilateral putamen, primary motor cortices, posterior cingulate cortex, ventromedial prefrontal cortex, and superior temporal/intraparietal sulci. Furthermore, the extents of these inhibition and execution activities were inversely correlated across subjects. On the basis of a median split of the stop signal reaction time (SSRT), subjects with short SSRT showed greater activity in the right orbital frontal cortex during preparatory inhibition. These new findings suggest that the go and stop processes interact prior to target presentation in the SST, in accord with recent computational models of stop signal inhibition.

Remembering forward: neural correlates of memory and prediction in human motor adaptation

We used functional MR imaging (FMRI), a robotic manipulandum and systems identification techniques to examine neural correlates of predictive compensation for spring-like loads during goal-directed wrist movements in neurologically-intact humans. Although load changed unpredictably from one trial to the next, subjects nevertheless used sensorimotor memories from recent movements to predict and compensate upcoming loads. Prediction enabled subjects to adapt performance so that the task was accomplished with minimum effort. Population analyses of functional images revealed a distributed, bilateral network of cortical and subcortical activity supporting predictive load compensation during visual target capture. Cortical regions--including prefrontal, parietal and hippocampal cortices--exhibited trial-by-trial fluctuations in BOLD signal consistent with the storage and recall of sensorimotor memories or "states" important for spatial working memory. Bilateral activations in associative regions of the striatum demonstrated temporal correlation with the magnitude of kinematic performance error (a signal that could drive reward-optimizing reinforcement learning and the prospective scaling of previously learned motor programs). BOLD signal correlations with load prediction were observed in the cerebellar cortex and red nuclei (consistent with the idea that these structures generate adaptive fusimotor signals facilitating cancelation of expected proprioceptive feedback, as required for conditional feedback adjustments to ongoing motor commands and feedback error learning). Analysis of single subject images revealed that predictive activity was at least as likely to be observed in more than one of these neural systems as in just one. We conclude therefore that motor adaptation is mediated by predictive compensations supported by multiple, distributed, cortical and subcortical structures.

Human basal ganglia and the dynamic control of force during on-line corrections

Natural movements are corrected in part by the generation of submovements, occurring early in a movement such that they amend an ongoing action. Submovements are associated with activity of the basal ganglia, implying a role for the structures in error correction. In parallel, the basal ganglia are linked to the generation and control of force amplitude, change, and duration. Here, we tested whether activity in human basal ganglia is associated with submovements generally, or was specific to a condition where the submovements only occurred in the face of unexpected proprioceptive error. Submovements were induced by introducing unexpected and variable viscous loads (augmenting the need for trial-specific grip forces) or by reducing target size (augmenting the need for visually guided on-line control) in a one-dimensional target-capture task. In both cases, subjects compensated for the increased task difficulty by generating corrective submovements, which were closely matched in frequency and type. Activity in the internal segment of the globus pallidus and subthalamic nucleus correlated strongly with the number of submovements during the viscous challenge but not with the target challenge. The effects could not be explained by kinematic differences, i.e., movement amplitude or average number of submovements. The results support a specific role for the basal ganglia in error correction under conditions of variable load where there is a need for the dynamic control of force within an ongoing movement.

Basal ganglia contributions to motor control: a vigorous tutor

The roles of the basal ganglia (BG) in motor control are much debated. Many influential hypotheses have grown from studies in which output signals of the BG were not blocked, but pathologically disturbed. A weakness of that approach is that the resulting behavioral impairments reflect degraded function of the BG per se mixed together with secondary dysfunctions of BG-recipient brain areas. To overcome that limitation, several studies have focused on the main skeletomotor output region of the BG, the globus pallidus internus (GPi). Using single-cell recording and inactivation protocols these studies provide consistent support for two hypotheses: the BG modulates movement performance ('vigor') according to motivational factors (i.e. context-specific cost/reward functions) and the BG contributes to motor learning. Results from these studies also add to the problems that confront theories positing that the BG selects movement, inhibits unwanted motor responses, corrects errors on-line, or stores and produces well-learned motor skills.

The cognitive neuroscience of prehension: recent developments

Prehension, the capacity to reach and grasp, is the key behavior that allows humans to change their environment. It continues to serve as a remarkable experimental test case for probing the cognitive architecture of goal-oriented action. This review focuses on recent experimental evidence that enhances or modifies how we might conceptualize the neural substrates of prehension. Emphasis is placed on studies that consider how precision grasps are selected and transformed into motor commands. Then, the mechanisms that extract action relevant information from vision and touch are considered. These include consideration of how parallel perceptual networks within parietal cortex, along with the ventral stream, are connected and share information to achieve common motor goals. On-line control of grasping action is discussed within a state estimation framework. The review ends with a consideration about how prehension fits within larger action repertoires that solve more complex goals and the possible cortical architectures needed to organize these actions.

Changing views of basal ganglia circuits and circuit disorders

The basal ganglia (BG) have long been considered to play an important role in the control of movement and the pathophysiology of movement disorders, such as Parkinson's disease (PD). Studies over the past decades have considerably broadened this view, indicating that the BG participate in multiple, parallel, largely segregated, cortico-subcortical reentrant pathways involving motor, associative and limbic functions. Research has shown that dysfunction within individual circuits is associated not only with movement disorders, but also with neuropsychiatric disorders. Accordingly, a number of movement disorders and neuropsychiatric disorders such as obsessive compulsive disorder and Tourette's syndrome are viewed as "circuit disorders." We here discuss the changes in our current understanding of the anatomic and functional organization of BG circuits and related circuit disorders.

Update on models of basal ganglia function and dysfunction

Circuit models of basal ganglia function and dysfunction have undergone significant changes over time. The previous view that the basal ganglia are centers in which massive convergence of cortical information occurred has now been replaced by a view in which these structures process information in a highly specific manner, participating in anatomical and functional modules that also involve cortex and thalamus. In addition, much has been learned about the intrinsic connections of the basal ganglia. While the basal ganglia-thalamocortical circuitry was originally seen almost exclusively in its relationship to the control of movement, these structures are now viewed as essential for higher level behavioral control, for instance in the regulation of habit learning or action selection. Probably the greatest benefit of these models has been that they have motivated a wealth of studies of the pathophysiology of movement disorders of basal ganglia origin, such as Parkinson's disease. Such studies, in turn, have helped to reshape the existing circuit models. In this paper we review these fascinating changes of our appreciation of the basal ganglia circuitry, and comment on the current state of our knowledge in this field.

Performance degradation and altered cerebral activation during dual performance: evidence for a bottom-up attentional system

Subjects performed a continuous tracking concurrently with an intermittent visual detection task to investigate the existence of competition for a capacity-limited stage (a bottleneck stage). Both perceptual and response-related processes between the two tasks were examined behaviorally and the changes in brain activity during dual-tasking relative to single-task were also assessed. Tracking error and joystick speed were analyzed for changes that were time-locked to visual detection stimuli. The associated brain activations were examined with functional magnetic resonance imaging (fMRI). These were analyzed using mixed block and event-related models to tease apart sustained neural activity and activations associated with individual events. Increased tracking error and decreased joystick speed were observed relative to the target stimuli in the dual-task condition only, which supports the existence of a bottleneck stage in response-related processes. Neuroimaging data show decreased activation to target relative to non-target stimuli in the dual-task condition in the left primary motor and somatosensory cortices controlling right-hand tracking, consistent with the tracking interference observed in behavioral data. Furthermore, the ventral attention system, rather than the dorsal attention system, was found to mediate task coordination between tracking and visual detection.