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Traditional measurement of multisensory facilitation in tasks such as speeded motor reaction tasks (MRT) consistently show age-related improvement during early childhood. However, the extent to which motor function increases with age and hence contribute to multisensory motor reaction times in young children has seldom been examined. Thus, we aimed to investigate the contribution of motor development to measures of multisensory (auditory, visual, and audiovisual) and visuomotor processing tasks in three young school age groups of children (n = 69) aged (5−6, n = 21; 7−8, n = 25.; 9−10 n = 18 years). We also aimed to determine whether age-related sensory threshold times for purely visual inspection time (IT) tasks improved significantly with age. Bayesian results showed decisive evidence for age-group differences in multisensory MRT and visuo-motor processing tasks, though the evidence showed that threshold time for visual identification IT performance was only slower in the youngest age group children (5−6) compared to older groups. Bayesian correlations between performance on the multisensory MRT and visuo-motor processing tasks indicated moderate to decisive evidence in favor of the alternative hypothesis (BF10 = 4.71 to 91.346), though not with the threshold IT (BF10 < 1.35). This suggests that visual sensory system development in children older than 6 years makes a less significant contribution to the measure of multisensory facilitation, compared to motor development. In addition to this main finding, multisensory facilitation of MRT within race-model predictions was only found in the oldest group of children (9−10), supporting previous suggestions that multisensory integration is likely to continue into late childhood/early adolescence at least. [ABSTRACT FROM AUTHOR]

Chewing gum and caffeine when used independently and concurrently increase neural activity ultimately improving reaction time but less is known about how caffeinated gum influences distinct phases of the reaction time response. Physically active college females (n=14) completed a 60-second reaction time test on a visuomotor board under the following counterbalanced conditions: 1) Baseline, 2) Non-caffeinated gum, 3) Caffeinated gum (300 mg caffeine). Point of application #1: Chewing gum improved premotor reaction time compared to baseline, but caffeine did not provide additional benefit. Point of application #2: Neither non-caffeinated nor caffeinated gum improved motor reaction times from baseline. Point of application #3: Chewing gum improved overall reaction time compared to baseline, but caffeine did not provide additional benefit. [ABSTRACT FROM AUTHOR]

Objectives: Aging is associated with cognitive decline, including visuomotor and memory concerns, and with motor system changes, including gait slowing and stooped posture. We investigated the associations of visuomotor performance and episodic memory with motor system characteristics in healthy older adults. Methods: Neurologically healthy older adults (N = 160, aged 50-89) completed a battery of cognitive and motor tasks. Cognitive variables were grouped by principal components analysis (PCA) into two components: visuomotor performance and verbal episodic memory. Our primary predictor variables were two aspects of motor function: timed-up-and-go (TUG) speed and neck angle. Additional predictor variables included demographic factors (age, sex and education) and indicators of physical fitness (body mass index/BMI and grip strength). All seven predictor variables were entered stepwise into a multiple regression model for each cognitive component. Results: Poor visuomotor performance was best predicted by a combination of advanced age, high BMI and slow TUG, whereas poor verbal memory performance was best predicted by a combination of advanced age, male sex, low education and acute neck angle. Conclusions: Upright posture and mobility were associated with different cognitive processes, suggesting different underlying neural mechanisms. These results provide the first evidence for a link between postural alignment and cognitive functioning in healthy older adults. Possible causal relationships are discussed. [ABSTRACT FROM AUTHOR]

Sensorimotor adaptation has traditionally been viewed as a purely error-based process. There is, however, growing appreciation for the idea that performance changes in these tasks can arise from the interplay of error-based adaptation with other learning processes. The challenge is to specify constraints on these different processes, elucidating their respective contributions to performance, as well as the manner in which they interact. We address this question by exploring constraints on savings, the phenomenon in which people show faster performance gains when the same learning task is repeated. In a series of five experiments, we demonstrate that error-based learning associated with sensorimotor adaptation does not contribute to savings. Instead, savings reflects improvements in action selection, rather than motor execution. [ABSTRACT FROM AUTHOR]

Driver behavior and vehicle-road kinematics have been shown to change over prolonged periods of driving; however, the interaction between these two indices has not been examined. Here we develop a measure that examines how drivers turn the steering wheel relative to heading error velocity, which the authors call the relative steering wheel compensation (RSWC). The RSWC transiently changes on a short time scale coincident with a verbal query embedded within the study paradigm. In contrast, more traditional variables are dynamic over longer time scales consistent with previous research. The results suggest drivers alter their behavioral output (steering wheel correction) relative to sensory input (vehicle heading error velocity) on a distinct temporal scale and may reflect an interaction of alerting and control. [ABSTRACT FROM AUTHOR]

Given that visual estimation of an object's size is affected by an illusory figure, the present study investigates the Ebbinghaus size-illusion effect on visuomotor performance within different preview durations for viewing an object (no preview, 300, 700, 1500, and 3000 ms) before initiating the movement. Twenty participants performed the following actions: (a) grasping the object and (b) matching the perceived object size with the finger aperture configuration as in the grasping task. The illusion affected the grasping aperture size only in the no- and 300-ms preview durations, while the matching aperture was affected across all preview conditions. These results suggest that the preview duration influences the size illusion to affect the grasping performance, and subjects adopt different visuomotor processes, depending on preview duration. [ABSTRACT FROM PUBLISHER]

When interpreting other people's movements or actions, observers may not only rely on the visual cues available in the observed movement, but they may also be able to "put themselves in the other person's shoes" by engaging brain systems involved in both "mentalizing" and motor simulation. The ageing process brings changes in both perceptual and motor abilities, yet little is known about how these changes may affect the ability to accurately interpret other people's actions. Here we investigated the effect of ageing on the ability to discriminate the weight of objects based on the movements of actors lifting these objects. Stimuli consisted of videos of an actor lifting a small box weighing 0.05-0.9 kg or a large box weighting 3-18 kg. In a four-alternative forced-choice task, younger and older participants reported the perceived weight of the box in each video. Overall, older participants were less sensitive than younger participants in discriminating the perceived weight of lifted boxes, an effect that was especially pronounced in the small box condition. Weight discrimination performance was better for the large box compared to the small box in both groups, due to greater saliency of the visual cues in this condition. These results suggest that older adults may require more salient visual cues to interpret the actions of others accurately. We discuss the potential contribution of age-related changes in visual and motor function on the observed effects and suggest that older adults' decline in the sensitivity to subtle visual cues may lead to greater reliance on visual analysis of the observed scene and its semantic context. [ABSTRACT FROM AUTHOR]

The underlying neural mechanisms of a perceptual bias for in-phase bimanual coordination movements are not well understood. In the present study, we measured brain activity with functional magnetic resonance imaging in healthy subjects during a task, where subjects performed bimanual index finger adduction-abduction movements symmetrically or in parallel with real-time congruent or incongruent visual feedback of the movements. One network, consisting of bilateral superior and middle frontal gyrus and supplementary motor area (SMA), was more active when subjects performed parallel movements, whereas a different network, involving bilateral dorsal premotor cortex (PMd), primary motor cortex, and SMA, was more active when subjects viewed parallel movements while performing either symmetrical or parallel movements. Correlations between behavioral instability and brain activity were present in right lateral cerebellum during the symmetric movements. These findings suggest the presence of different error-monitoring mechanisms for symmetric and parallel movements. The results indicate that separate areas within PMd and SMA are responsible for both perception and performance of ongoing movements and that the cerebellum supports symmetric movements by monitoring deviations from the stable coordination pattern. [ABSTRACT FROM AUTHOR]

The circuits that drive visually guided eye and arm movements trans- form generic visual inputs into effector-specific motor commands. As part of the effort to elucidate these circuits, the primate lateral intra-parietal area (LIP) has been interpreted as a priority map for saccades (oculomotor-specific) or a salience map of space (not effector-specific). It has also been proposed as a locus for eye-hand coordination. We reversibly inactivated LIP while monkeys performed memory-guided saccades and reaches. Coordinated saccade and reach reaction times were similarly impaired, consistent with a nonspecific role. However, reaches made without an accompanying saccade remained intact. and the relative temporal coupling of saccades and reaches was unchanged. These results suggest that LIP contributes to saccade planning but not to reach planning. Coordinated reaches are delayed as a result of an eye-hand coordination mechanism, located outside of UP, that actively delays reaches until shortly after the onset of an associated saccade. We condude with a discussion of how to reconcile specificity for saccades with a possible role in directing attention. [ABSTRACT FROM AUTHOR]

Abstract: In contrast to conventional reaction time (RT) tasks, saccadic RT’s to visual targets are very fast and unaffected by the number of possible targets. This can be explained by the sub-cortical circuitry underlying eye movements, which involves direct mapping between retinal input and motor output in the superior colliculus. Here we asked if the choice-invariance established for the eyes also applies to a special class of fast visuomotor responses of the upper limb. Using a target-pointing paradigm we observed very fast reaction times (<150ms) which were completely unaffected as the number of possible target choices was increased from 1 to 4. When we introduced a condition of altered stimulus–response mapping, RT went up and a cost of choice was observed. These results can be explained by direct mapping between visual input and motor output, compatible with a sub-cortical pathway for visual control of the upper limb. [Copyright &y& Elsevier]

Abstract: The model of a stochastic decision process unfolding in motor and premotor regions of the brain was encoded in single-trial magnetoencephalographic (MEG) recordings while ten healthy subjects performed a sensorimotor Reaction Time (RT) task. The duration of single-trial MEG signals preceding the motor response, recorded over the motor cortex contralateral to the responding hand, co-varied with RT across trials according to the model''s prediction. Furthermore, these signals displayed the same properties of a “rising-to-a-fixed-threshold” decision process as posited by the model and observed in the activity of single neurons in the primate cortex. The present findings demonstrate that non-averaged, single-trial MEG recordings can be used to test models of cognitive processes, like decision-making, in humans. [Copyright &y& Elsevier]

Background: Several studies have found correlations between proprioception and visuomotor function during stroke recovery, however two more recent studies have found no correlation. Unfortunately, most of the studies to date have been conducted with clinical assessments of sensation that are observer-based and have poor reliability. We have recently developed new tests to assess position sense and motor function using robotic technology. The present study was conducted to reassess the relationship between position sense and upper limb movement following stroke. Methods: We assessed position sense and motor performance of 100 inpatient stroke rehabilitation subjects and 231 non-disabled controls. All subjects completed quantitative assessments of position sense (arm-position matching task) and motor performance (visually-guided reaching task) using the KINARM robotic device. Subjects also completed clinical assessments including handedness, vision, Purdue Pegboard, Chedoke-McMaster Stroke Assessment-Impairment Inventory and Functional Independence Measure (FIM). Neuroimaging documented lesion localization. Fisher's exact probability tests were used to determine the relationship between performances on the arm-position matching and visually-guided reaching task. Pearson's correlations were conducted to determine the relationship between robotically measured parameters and clinical assessments. Results: Performance by individual subjects on the matching and reaching tasks was statistically independent (Fisher's test, P<0.01). However, performance on the matching and reaching tasks both exhibited relationships with abilities in daily activities as measured by the FIM. Performance on the reaching task also displayed strong relationships with other clinical measures of motor impairment. Conclusions: Our data support the concept that position sense deficits are functionally relevant and point to the importance of assessing proprioceptive and motor impairments independently when planning treatment strategies. [ABSTRACT FROM AUTHOR]

We report data examining the relations between endogenous allocation of visual attention and effects of motor-preparation on attention. We tested a patient with a spatial bias in perceptual report following damage to the left inferior parietal lobe and superior temporal gyrus. Previously we have shown that the spatial bias in report can be reduced when a movement is planned to where a target falls in the contralesional field, while the bias is exacerbated when a movement is planned to the ipsilesional side (Kitadono & Humphreys, 2007, Cognitive Neuropsychology, 24). Here we pitted the effects of planning a movement to the contra- or ipsilesional side against the effects of endogenous visual attention, manipulated by varying the probability of where a target would fall. In a no-movement baseline, there was better identification of contralesional targets when there was a good likelihood of targets appearing on the contralesional side (the 20-80 and 50-50 conditions) compared with when targets had a low probability of occurring there (the 80-20 condition). This sensitivity to target probability interacted with the effects of planning a movement to the contra- or ipsilesional side. When the target had a good probability of falling in the contralesional field (the 20-80 and 50-50 conditions), planning a movement to the ipsilesional side disrupted contralesional report. When there was a high probability of an ipsilesional target (the 80-20 condition), planning a movement to a congruent side improved contralesional report. The results indicate that effects of endogenous attention and of motor-based attention influence a common system controlling visual orienting. [ABSTRACT FROM AUTHOR]

The ability to correct reaching movements for changes in target position has been described as the hand's 'automatic pilot'. These corrections are preconscious and occur by default in double-step reaching tasks, even if the goal is to react to the target jump in some other way, for instance by stopping the movement (STOP instruction). Nonetheless, corrections are strongly modulated by conscious intention: participants make more corrections when asked to follow the target (GO instruction) and can suppress them when explicitly asked not to follow the target (NOGO instruction). We studied the influence of a cognitively demanding (auditory 1-back) task upon correction behaviour under GO, STOP and NOGO instructions. Correction rates under the STOP instruction were unaffected by cognitive load, consistent with the assumption that they reflect the default behaviour of the automatic pilot. Correction rates under the GO instruction were also unaffected, suggesting that minimal cognitive resources are required to enhance online correction. By contrast, cognitive load impeded the ability to suppress online corrections under the NOGO instruction. These data reveal a constitutional bias in the automatic pilot system: intentional suppression of the default correction behaviour is cognitively demanding, but enhancement towards greater responsiveness is seemingly effortless. [ABSTRACT FROM AUTHOR]

Abstract: As part of an ongoing investigation into real-world copying and drawing, I recorded the eye–hand drawing strategies of 16 subjects with drawing experiences ranging from expert to novice while they copied a line drawing of a standing nude. The experts produced accurate copies whereas all the beginners produced marked inaccuracies of overall scaling, proportion and shape. Analysis of eye and hand movements showed that the experts alone segmented the original drawing into simple line sections that were copied one at a time using a direct eye–hand strategy not requiring intermediary encoding to visual memory. The results suggest that segmentation into simple lines defines the task-specific process of accurate copying, and that this process is restricted to experts, i.e. acquired through training and practice. Additional preliminary tests also suggest that a similar process may apply to drawing a model from life. [Copyright &y& Elsevier]

Abstract: Evidence from studies in both animals and humans suggests that pharmacological stimulation of the noradrenergic system may modulate cortical excitability. However, the influence of such a modulation on the motor system remains unclear. We here explored the effects of noradrenergic stimulation on different motor tasks with increasing complexity and sensorimotor demands. Healthy human subjects received either reboxetine – a selective noradrenaline reuptake inhibitor – or placebo in a double-blind within-subject design. The analysis of movement kinematics revealed differential effects of RBX on subjects’ motor performance. While isolated stereotypic finger movements and simple reach-to-grasp movements did not change under RBX stimulation (compared to placebo), subjects showed a significant gain in movement speed in visuomotor tasks requiring online-control of precision movements. The results suggest that stimulating the noradrenergic system via RBX does not influence motor performance in general, but rather supports neural circuits involved in visuomotor control of movements. [Copyright &y& Elsevier]

Much work indicates that parietal cortex mediates the transformation of visual information into the motor commands necessary for successful performance of many unimanual tasks. Accumulating evidence suggests that parietal cortex also mediates the coordination of bimanual movements, during which the natural tendency is to couple the limbs temporally. However, the extent to which parietal oculomotor and/or visual processes contribute to temporal coupling of the limbs during bimanual task performance is unknown. In the current study, we monitored the eye movements of a patient with a left parietal infarction as she performed a series of bimanual visuomotor tasks. We demonstrate the impact of an ipsilesional (leftward) orientation bias on her ability to synchronize the onset of bimanual limb movements; the movements were performed in serial fashion, i.e., left limb before right, when the patient was permitted to freely shift saccades and the visual target cuing the left (ipsilesional) limb movement was presented at greater (leftward) eccentricities. Disruption of interlimb synchrony as such was not, however, evident when the patient was required to fixate or when visual targets were presented at lesser ipsilesional eccentricities. Additionally, despite the disruptive influence of oculomotor and visual factors on interlimb synchrony, the patient appeared capable of using visual feedback to straighten the right (contralesional) limb trajectory, thus improving the spatial component of task performance. Results suggest that parietal cortex plays an important role in the coordination of limb movements during performance of bimanual visuomotor tasks. This role appears to involve orienting gaze or attention to the goals of each limb so that the nervous system can synchronize the activity of both limbs and thereby ensure successful task completion. [ABSTRACT FROM AUTHOR]

It has been suggested that the metrics of grasping movements directed to visible objects are controlled in real time and are therefore unaffected by previous experience. We tested whether the properties of a visually presented distractor object influence the kinematics of a subsequent grasping movement performed under full vision. After viewing an elliptical distractor object in one of two different orientations participants grasped a target object, which was either the same object with the same orientation or a circular object without obvious orientation. When grasping the circular target, grip orientation was influenced by the orientation of the distractor. Moreover, as in classical visuomotor priming, grasping movements were initiated faster when distractor and target were identical. Results provide evidence that planning of visually guided grasping movements is influenced by prior perceptual experience, challenging the notion that metric aspects of grasping are controlled exclusively on the basis of real-time information. [ABSTRACT FROM AUTHOR]

Abstract: Positron emission tomography (PET) was used to investigate differences in neural plasticity associated with learning a unique motor task in patients with schizophrenia and healthy volunteers. Working with a robotic manipulandum, subjects learned reaching movements in a force field. Visual cues were provided to guide the reaching movements. PET rCBF measures were acquired while participants learned the motor skill over successive runs. The groups did not differ in behavioral performance but did differ in their rCBF activity patterns. Healthy volunteers displayed blood flow increases in primary motor cortex and supplementary motor area with motor learning. The patients with schizophrenia displayed an increase in the primary visual cortex with motor learning. Changes in these regions were positively correlated with changes in each group''s motor accuracy, respectively. This is the first study to employ a unique arm-reaching motor learning test to assess neural plasticity during multiple phases of motor learning in patients with schizophrenia. The patients may have an inability to rapidly tune motor cortical neural populations to a preferred direction. The visual system, however, appears to be highly compensated in schizophrenia and the inability to rapidly modulate the motor cortex may be substantially corrected by the schizophrenic group''s visuomotor adaptations. [Copyright &y& Elsevier]

Abstract: Several sensory–motor integration regions have been identified in parietal cortex, which appear to be organized around motor-effectors (e.g., eyes, hands). We investigated whether a sensory–motor integration area might exist for the human vocal tract. Speech requires extensive sensory–motor integration, as does other abilities such as vocal musical skills. Recent work found that a posterior superior temporal-parietal region, area Spt, has both sensory (auditory) and motor response properties (for both speech and tonal stimuli). Brain activity of skilled pianists was measured with fMRI while they listened to a novel melody and either covertly hummed the melody (vocal tract effectors) or covertly played the melody on a piano (manual effectors). Activity in area Spt was significantly higher for the covert hum versus covert play condition. A region in the anterior IPS (aIPS) showed the reverse pattern, suggesting its involvement in sensory-manual transformations. This finding suggests that area Spt is a sensory–motor integration area for vocal tract gestures. [Copyright &y& Elsevier]

During the last 10 years a considerable number of neurophysiological and functional imaging studies have provided evidence that observation and execution of movements activate common representations. Furthermore, several behavioural studies suggest that action observation can influence the performance of movements. Recently it was shown that viewing incongruent movements interferes with the execution of non-object oriented sinusoidal arm movements (Kilner et al. in Curr Biol 13:522–525, ). In the current study, we investigated whether interference of action observation also occurs during goal-directed prehension movements. Participants were required to grasp cubes of different sizes while simultaneously observing an actor performing grasping or pointing movements. The actors’ movement could be directed at objects that were identical, or different in size to the cube grasped by the participant. The results showed that maximum grip aperture was affected by observation of grasping towards larger objects. No effect of object size was found during observation of pointing movements. These results suggest that observation of grasping movements can interfere with the on-line control of prehension movements and provides further evidence for overlapping networks for grasping observation and execution. [ABSTRACT FROM AUTHOR]

Abstract: Lesions of the parieto-occipital junction (POJ) in humans cause gross deviations of reaching movements and impaired grip formation if the targets are located in the subjects’ peripheral visual field. Movements to central targets are typically less impaired. This disorder has been termed “optic ataxia”. It has been suggested that a general deficit of online corrections under central as well as peripheral viewing conditions might be sufficient to explain this discrepancy. According to this hypothesis, patients with optic ataxia should demonstrate an impaired online correction of grip aperture under central viewing conditions if the target object changes its size during the grasping movement. We investigated this prediction in a patient with optic ataxia (I.G.) in a virtual visuo-haptic grasping task. We imposed an isolated need for online corrections of the hand aperture independently of positional changes of the target object. While we found some general inaccuracies of her grasping movements, the patient did not show a specific impairment of online adjustment of grip aperture. On the contrary, I.G. smoothly adjusted her grip aperture comparable to healthy subjects. A general deficit of fast movement correction affecting targets in peripheral as well as central visual fields thus does not appear to account for the overt visuomotor deficits in optic ataxia. Rather, it seems more likely that an anatomical dissociation between visuomotor pathways related to actions in the central and in the peripheral visual field underlies the dissociation of visuomotor performance depending on the retinotopic target position in optic ataxia. [Copyright &y& Elsevier]

Abstract: Craighero et al. [Craighero, L., Fadiga, U., Umiltà, C.A., & Rizzolatti, G. (1996). Evidence for visuomotor priming effect. Neuroreport, 8, 347–349] showed that grasping movements were initiated more quickly when the goal object shared the same orientation as a previously seen ‘prime’ object. Because the goal object was never visible in these experiments, however, it is unclear whether the data should be construed as evidence for a general visuomotor priming effect (as the authors contend), or only as evidence for a more specific priming effect on memory-guided actions. In Experiment 1, we demonstrated that memory-guided but not visually guided grasping can be primed by passive viewing of a prime object. In Experiment 2, we compared the effects of a prime object on the grasping and naming of a visible target object. Participants were faster to name the target when its shape was the same as the prime, consistent with well-established perceptual priming effects. Under the identical set of testing parameters, however, reaction time for grasping was unaffected by the orientation or the shape of the prime. In Experiment 3, participants grasped the goal object after either viewing or grasping a prime object. Reaction time for grasping was unaffected by the visual features of the prime in both tasks. Taken together, these results are consistent with the view that perceptual memory – which presumably underlies visual priming effects – is largely irrelevant for programming the metrics of actions to visible objects. Visually guided actions are programmed in real-time by dedicated visuomotor modules that appear to be insensitive to the priming effects that are a hallmark of visual perception. [Copyright &y& Elsevier]

In various studies subjects have been shown to misperceive the positions of targets that are flashed during pursuit eye movements. They mislocalise them in the direction of pursuit. Nevertheless, Hansen (1979) found that subjects accurately hit targets that are flashed during pursuit with a quick hammer blow. We examined whether this is because there is a fundamental difference between the information that determines our perceptual judgements of a target’s position and the information that is used to guide our hand to a similar target. Subjects were asked to quickly tap targets that were flashed during pursuit with their index finger. They systematically tapped ahead of the position of the flash, in accordance with the above-mentioned perceptual mislocalisations. Thus the lack of systematic errors in Hansen’s study is not a general property of fast motor responses. [ABSTRACT FROM AUTHOR]

Eye–hand coordination is geometrically complex. To compute the location of a visual target relative to the hand, the brain must consider every anatomical link in the chain from retinas to fingertips. Here we focus on the first three links, studying how the brain handles information about the angles of the two eyes and the head. It is known that people, even in darkness, reach more accurately when the eye looks toward the target, rather than right or left of it. We show that reaching is also impaired when the binocular fixation point is displaced from the target in depth: reaching becomes not just sloppy, but systematically inaccurate. Surprisingly, though, in normal Gaze-On-Target reaching we found no strong correlations between errors in aiming the eyes and hand onto the target site. We also asked people to reach when the head was not facing the target. When the eyes were on-target, people reached accurately, but when gaze was off-target, performance degraded. Taking all these findings together, we suggest that the brain's computational networks have learned the complex geometry of reaching for well-practiced tasks, but that the networks are poorly calibrated for less common tasks such as Gaze-Off-Target reaching. [ABSTRACT FROM AUTHOR]

If an object changes position at the onset of a reach-to-grasp movement, both the transport speed and the grip aperture are adjusted. If the object changes in size at the onset, only the grip aperture is adjusted. This combination of results has been interpreted as being the consequence of a hierarchical relationship between visuomotor channels for transport and grip. We argue that our alternative view on grasping can account for the observed behaviour without making new assumptions. In our view, grasping consists of smooth (minimal jerk) movements of each digit to a target position on the object. The digits’ target positions change, both when object position and when object size change. A model in which the individual digits move smoothly to these new positions yields the same behaviour as is observed experimentally. [Copyright &y& Elsevier]

Dysfunction of the cerebellum leads to significant deterioration of movements performed under visual guidance and of co-ordinated eye and hand movement. Visually guided tracking tasks combine both of these control features, as the eyes and hand together track a visual target. To better understand the involvement of the cerebellum in tracking tasks, we used functional magnetic-resonance imaging to study the activation of cerebellar structures in visually guided tracking movements of the eye and hand. Subjects were tested performing ocular tracking, manual tracking without eye movement or combined eye and hand tracking of a smoothly moving visual target. Three areas were activated in the cerebellum: a bilateral region in the ansiform lobule of the lateral hemisphere, a region in the ipsilateral paramedian lobule and a region in the oculomotor vermis. The ansiform and paramedian areas were most strongly activated by hand movement, although the vermal site was also active. The reverse was found for ocular tracking, with predominantly vermal activation. Activation of these cerebellar cortical areas related to movement of eyes or hand alone was significantly enhanced when the subjects performed co-ordinated eye and hand tracking of a visual target. These results provide the first direct evidence from a functional-imaging study for cerebellar activation in eye and hand co-ordination. [ABSTRACT FROM AUTHOR]