Unimanual Motor Research Articles

Aging, aerobic activity and interhemispheric communication.

Recent studies have shown that during unimanual motor tasks, aging adults show bilateral recruitment of primary motor cortex (M1), while younger adults show a suppression of the ipsilateral motor cortex. Additional work has indicated that increased bilateral M1 recruitment in older adults may be deleterious when performing some motor tasks. However, higher levels of physical fitness are associated with improved dexterity and fitness may mitigate the loss of both inhibitory and excitatory communication in aging adults. The goal of this study was to assess dexterity and interhemispheric motor communication in physically fit and sedentary middle-age (40–60 years) right handed participants using tests of hand deftness and transcranial magnetic stimulation (TMS). To behaviorally assess the influence of interhemispheric communication on motor performance, participants also perform the coin rotation deftness task while maintaining pinch force with the opposite hand (bimanual condition). We correlated these behavioral measures with the ipsilateral silent period using TMS to assess interhemispheric inhibition. Our results show that the middle-aged adults who were physically fit had better dexterity of their right hand (finger tapping and peg-board). When performing the coin rotation task the fit group had no between hand differences, but the sedentary group’s left hand performance was inferior to the their right hand. We found that better dexterity correlated with ipsilateral silent period duration (greater inhibition) thereby supporting the postulate that fitness improves interhemispheric motor communication.

Interhemispheric control of unilateral movement.

To perform strictly unilateral movements, the brain relies on a large cortical and subcortical network. This network enables healthy adults to perform complex unimanual motor tasks without the activation of contralateral muscles. However, mirror movements (involuntary movements in ipsilateral muscles that can accompany intended movement) can be seen in healthy individuals if a task is complex or fatiguing, in childhood, and with increasing age. Lateralization of movement depends on complex interhemispheric communication between cortical (i.e., dorsal premotor cortex, supplementary motor area) and subcortical (i.e., basal ganglia) areas, probably coursing through the corpus callosum (CC). Here, we will focus on transcallosal interhemispheric inhibition (IHI), which facilitates complex unilateral movements and appears to play an important role in handedness, pathological conditions such as Parkinson's disease, and stroke recovery.

Task-specific modulation of effective connectivity during two simple unimanual motor tasks: A 122-channel EEG study

Neural oscillations are thought to underlie coupling of spatially remote neurons and gating of information within the human sensorimotor system. Here we tested the hypothesis that different unimanual motor tasks are specifically associated with distinct patterns of oscillatory coupling in human sensorimotor cortical areas. In 13 healthy, right-handed subjects, we recorded task-induced neural activity with 122-channel electroencephalography (EEG) while subjects performed fast self-paced extension-flexion movements with the right index finger and an isometric contraction of the right forearm. Task-related modulations of inter-regional coupling within a core motor network comprising the left primary motor cortex (M1), lateral premotor cortex (lPM) and supplementary motor area (SMA) were then modeled using dynamic causal modeling (DCM). A network model postulating coupling both within and across frequencies best captured observed spectral responses according to Bayesian model selection. DCM revealed dominant coupling within the β-band (13-30 Hz) between M1 and SMA during isometric contraction of the forearm, whereas fast repetitive finger movements were characterized by strong coupling within the γ-band (31-48 Hz) and between the θ- (4-7 Hz) and the γ-band. This coupling pattern was mainly expressed in connections from lPM to SMA and from lPM to M1. We infer that human manual motor control involves task-specific modulation of inter-regional oscillatory coupling both within and across distinct frequency bands. The results highlight the potential of DCM to characterize context-specific changes in coupling within functional brain networks.

Interhemispheric Plasticity in Humans

Chronic unimanual motor practice increases the motor output not only in the trained but also in the nonexercised homologous muscle in the opposite limb. We examined the hypothesis that adaptations in motor cortical excitability of the nontrained primary motor cortex (iM1) and in interhemispheric inhibition from the trained to the nontrained M1 mediate this interlimb cross education. Healthy, young volunteers (n=12) performed 1000 submaximal voluntary contractions (MVC) of the right first dorsal interosseus (FDI) at 80% MVC during 20 sessions. Trained FDI's MVC increased 49.9%, and the untrained FDI's MVC increased 28.1%. Although corticospinal excitability in iM1, measured with transcranial magnetic stimulation (TMS) before and after every fifth session, increased 6% at rest, these changes, as those in intracortical inhibition and facilitation, did not correlate with cross education. When weak and strong TMS of iM1 were delivered on a background of a weak and strong muscle contraction, respectively, of the right FDI, excitability of iM1 increased dramatically after 20 sessions. Interhemispheric inhibition decreased 8.9% acutely within sessions and 30.9% chronically during 20 sessions and these chronic reductions progressively became more strongly associated with cross education. There were no changes in force or TMS measures in the trained group's left abductor minimi digiti and there were no changes in the nonexercising control group (n=8). The findings provide the first evidence for plasticity of interhemispheric connections to mediate cross education produced by a simple motor task.

Typical and atypical (cerebral palsy) development of unimanual and bimanual grasp planning

In the present study we tested 13 children with cerebral palsy (CP) and 24 typically developing children (7–12 years old) in a unimanual and bimanual motor planning task. We focused on two research questions: (1) How does motor planning develop in children with and without CP? and (2) Is motor planning facilitated when the task is performed with both hands? Participants had to grasp one or two vertical oriented cylinder(s) and transport it/them to a platform that had different heights. As a measure of motor planning, we registered the height at which participants grasped the cylinder. Here, anticipation of grasp height upon the height of the upcoming target(s) is reflective of proper forward motor planning as it leads to a comfortable posture at the end of the task. In the unimanual task the typically developing children showed a significant grasp height effect, which increased with age. In contrast, no grasp height effect, or age related changes therein were found for the children with CP, suggesting a compromised development of motor planning in these children. Interestingly, when children had to transport one cylinder to a high shelf and one cylinder to a low shelf, the more affected hand of the CP children clearly anticipated the grasp height to the upcoming target height. The less affected hand did not show such anticipation. Taken collectively, these findings suggest a delayed or compromised development of motor planning in children with CP compared to typically developing children. At the same time, the facilitated motor planning of the more affected arm in the bimanual task offers a valuable entry point for intervention to improve motor planning in CP.

Associations between sensorimotor impairments and motor ability deficits: the pieces of the puzzle are beginning to fall into place

Many studies on children with cerebral palsy (CP) have provided elegant and detailed descriptions of sensorimotor impairments (also referred to as negative and positive signs of upper motor neuron lesions) and have sought to describe associations between these impairments and deficits in motor abilities. However, efforts in the past to find quantifiable and clinically meaningful relationships between deficits in sensorimotor function and activity limitations have largely been elusive. A metaphor for this situation is that each identified impairment is like one piece of a large jigsaw puzzle. Although the size and shape of each puzzle piece can be clearly characterized, the question of how to orient each piece in order to determine how it contributes to the larger picture – in this case the motor function or activity – is much harder to resolve. Sakzewski et al.1 have taken an important positive step in this direction. In their cross-sectional study of 70 children with hemiplegic CP, two important findings emerge – a moderate correlation between sensory deficits in the hand and unimanual motor capacity; and a strong correlation between unimanual capacity and bimanual performance. Why have these authors found these relationships when others have failed? Several factors may have been at play here. One factor is that the study included a large enough sample of participants so that meaningful statistical and clinical relationships could be found using appropriate statistical models. Another key element to their success is the use of the unifying theoretical framework of the International Classification of Functioning, Disability and Health (ICF) within which to arrange their puzzle pieces.2 The ICF not only provides a structure for classification of components of mobility but also a means to establish clear terminology within and between hierarchical levels. Indeed, the structure of the ICF itself implies relationships between elements at each level and between levels without specifying the exact nature of these relationships. Sakzewski et al.1 chose valid and reliable outcome measures reflecting a broad spectrum of functioning, that were effective measures of their desired constructs at two levels of the ICF framework. By their judicious use of outcome measures chosen to address specific aspects of motor function within the framework of the ICF, Sakzewski et al. were able to describe these relationships with respect to impairments and activities at the arm and hand level. Their second major finding, the relationship between unimanual and bimanual arm function, was found using two recently described measures – the Melbourne Assessment of Unilateral Upper Limb Function3 and the Assisting Hand Assessment.4 These two measures have undergone rigorous development and validity and reliability testing in the population investigated. More importantly, both measures are based on constructs that have ecological validity, and thus they may better reflect the desired constructs than earlier clinical measures. The use of these measures may help explain why the previous elusive relationship between unimanual and bimanual deficits can now be described. The results of Sakzewski et al.’s study represent an important step forward in our understanding of the relationship between arm impairments, unimanual function, and bimanual performance in children with hemiplegia. Insights into these relationships can be used by clinicians to guide treatment interventions for improving arm and hand function. The next essential step is to determine if, indeed, training of the impaired upper limb will impact bimanual performance in a meaningful way leading to greater participation of the child across the spectrum of life activities.5

The Use of Kinetics as a Marker for Manual Dexterity After Stroke and Stroke Recovery

Stroke is the leading cause of severe, long-term disability among older adults in the United States. Unimanual motor performance of the hemiparetic limb is clearly compromised, and these declines are well documented. An often overlooked aspect of motor function for patients with stroke is the effect of unilateral motor dysfunction on bimanual motor activities. Diminished bimanual function resulting from upper extremity hemiparesis necessarily limits the patient’s daily functioning. In this review we describe a bimanual dexterity task that replicates many daily activities and outline how kinetic analysis of this task may provide insight into diminished bimanual function of patients with stroke and how these variables may be useful in assessing level of recovery and rate of motor recovery associated with behavioral interventions intended to improve upper extremity function. It is argued that the use of objective kinetic measures to quantify hand function may facilitate the clinical adoption of behavioral interventions for stroke, such as constraint-induced movement therapy and other repetitive task practice-based interventions.

Functional Neuroanatomy of Mirroring during a Unimanual Force Generation Task

Performance of a unimanual motor task often induces involuntary mirror electromyographic (EMG) activity in the opposite, resting hand. In spite of the ubiquitous presence of mirroring, little is known regarding the underlying cortical contributions. Here, we used functional magnetic resonance imaging (fMRI) to study brain regions activated in association with parametric increases in right isometric wrist flexion force (10%, 20%, 30%, and 70%) in 12 healthy volunteers. During scanning, EMG activity was recorded bilaterally from flexor carpi radialis (FCR), extensor carpi radialis (ECR), biceps brachii (BB), and triceps brachii (TB). Mirror EMG was observed in left FCR during 20%, 30%, and 70% of force. Left ECR, BB, and TB showed mirror EMG only at 70% of force. Increasing force was associated with a linear increase of blood-oxygen-level-dependent (BOLD) signal in bilateral primary motor cortex (M1), supplementary motor area (SMA), caudal cingulate, and cerebellum. Mirroring in the left FCR correlated with activity in bilateral M1, SMA, and the cerebellum. Overall, our results suggest that activity in these regions might reflect sensorimotor processes operating in association with mirroring and suggest caution when interpreting fMRI activity in studies that involve unilateral force generation tasks in the absence of simultaneous bilateral EMG/kinematics measurements.

Scaling of motor cortical excitability during unimanual force generation

During performance of a unimanual force generation task primary motor cortices (M1s) experience clear functional changes. Here, we evaluated the way in which M1s interact during parametric increases in right wrist flexion force in healthy volunteers. We measured the amplitude and the slope of motor evoked potentials (MEP) recruitment curves to transcranial magnetic stimulation (TMS) in the left and right flexor carpi radialis (FCR) muscles at rest and during 10%, 30% and 70% of maximal wrist flexion force. At rest, no differences were observed in the amplitude and slope of MEP recruitment curves in the left and right FCR muscles. With increasing right wrist flexion force, MEP amplitudes increased in both FCR muscles, with larger amplitudes in the right FCR. We found a significant correlation between the left and right MEP amplitudes across conditions. The slope of right and left FCR MEP recruitment curve was significantly steeper at 70% of force compared to rest and 10% of force. A significant correlation between the slope of left and right FCR MEP amplitudes was found at 70% of force only. Our results indicate a differential scaling of excitability in the corticospinal system controlling right and left FCR muscles at increasing levels of unimanual force generation. Specifically, these data highlights that at strong levels of unimanual force the increases in motor cortical excitability with increasing TMS stimulus intensities follow a similar pattern in both M1s, while at low levels of force they do not.

Levodopa-sensitive, dynamic changes in effective connectivity during simultaneous movements in Parkinson's disease

Changes in effective connectivity during the performance of a motor task appear important for the pathogenesis of motor symptoms in Parkinson's disease (PD). One type of task that is typically difficult for individuals with PD is simultaneous or bimanual movement, and here we investigate the changes in effective connectivity as a potential mechanism. Eight PD subjects off and on l-DOPA medication and 10 age-matched healthy control subjects performed both simultaneous and unimanual motor tasks in an fMRI scanner. Changes in effective connectivity between regions of interest (ROIs) during simultaneous and unimanual task performance were determined with structural equation modeling (SEM), and changes in the temporal dynamics of task performance were determined with multivariate autoregressive modeling (MAR). PD subjects demonstrated alterations in both effective connectivity and temporal dynamics compared with control subjects during the performance of a simultaneous task. l-DOPA treatment was able to partially normalize effective connectivity and temporal patterns of activity in PD, although some connections remained altered in PD even after medication. Our results suggest that difficulty performing simultaneous movements in PD is at least in part mediated by a disruption of effective communication between widespread cortical and subcortical areas, and l-DOPA assists in normalizing this disruption. These results suggest that even when the site of neurodegeneration is relatively localized, study of how disruption in a single region affects connectivity throughout the brain can lead to important advances in the understanding of the functional deficits caused by neurodegenerative disease.

Interhemispheric motor inhibition: its role in controlling electromyographic mirror activity

Electromyographic mirror activity (MA) refers to involuntary activation of the non-active limb during intended strictly unilateral movements of the other limb. MA occurs in the majority of healthy adults but little is known about its neurophysiological foundation. Here we examined in healthy adults the hypothesis that transcallosal interhemispheric inhibition (IHI) between the primary motor cortices determines the extent to which MA occurs. IHI was tested by an established paired transcranial magnetic stimulation protocol [A. Ferbert et al. (1992) J. Physiol. (Lond.), 453, 525-546]. In a first experiment we found that the magnitudes of IHI and MA were inversely correlated. In a second experiment we sought to establish a more causative relation by exploring the changes induced by low-frequency repetitive transcranial magnetic stimulation of primary motor cortex on IHI and MA. These changes were also significantly inversely correlated, i.e. a repetitive transcranial magnetic stimulation-induced increase in IHI was associated with a decrease in MA, and a decrease in IHI was associated with an increase in MA. These results provide strong and consistent evidence that transcallosal inhibitory interhemispheric interaction provides a significant route by which unwanted MA during intended unimanual motor tasks can be controlled.

Mechanisms Underlying Functional Changes in the Primary Motor Cortex Ipsilateral to an Active Hand

Performance of a unimanual hand motor task results in functional changes in both primary motor cortices (M1(ipsilateral) and M1(contralateral)). The neuronal mechanisms controlling the corticospinal output originated in M1(ipsilateral) and the resting hand during a unimanual task remain unclear. Here, we assessed functional changes within M1(ipsilateral) and in interhemispheric inhibition (IHI) associated with parametric increases in unimanual force. We measured motor-evoked potential (MEP) recruitment curves (RCs) and short-interval intracortical inhibition (SICI) in M1(ipsilateral), IHI from M1(contralateral) to M1(ipsilateral), and the influence of IHI over SICI using transcranial magnetic stimulation at rest and during 10, 30, and 70% of maximal right wrist flexion force. EMG from the left resting flexor carpi radialis (FCR) muscle was comparable across conditions. Left FCR MEP RCs increased, and SICI decreased with increasing right wrist force. Activity-dependent (rest and 10, 30, and 70%) left FCR maximal MEP size correlated with absolute changes in SICI. IHI decreased with increasing force at matched conditioned MEP amplitudes. IHI and SICI were inversely correlated at increasing forces. In the presence of IHI, SICI decreased at rest and 70% force. In summary, we found activity-dependent changes in (1) SICI in M1(ipsilateral), (2) IHI from M1(contralateral) to M1(ipsilateral), and (3) the influence of IHI over SICI in the left resting hand during force generation by the right hand. Our findings indicate that interactions between GABAergic intracortical circuits mediating SICI and interhemispheric glutamatergic projections between M1s contribute to control activity-dependent changes in corticospinal output to a resting hand during force generation by the opposite hand.

Hemispheric Asymmetry of Frequency-Dependent Suppression in the Ipsilateral Primary Motor Cortex During Finger Movement: A Functional Magnetic Resonance Imaging Study

Electrophysiological studies have suggested that the activity of the primary motor cortex (M1) during ipsilateral hand movement reflects both the ipsilateral innervation and the transcallosal inhibitory control from its counterpart in the opposite hemisphere, and that their asymmetry might cause hand dominancy. To examine the asymmetry of the involvement of the ipsilateral motor cortex during a unimanual motor task under frequency stress, we conducted block-design functional magnetic resonance imaging with 22 normal right-handed subjects. The task involved visually cued unimanual opponent finger movement at various rates. The contralateral M1 showed symmetric frequency-dependent activation. The ipsilateral M1 showed task-related deactivation at low frequencies without laterality. As the frequency of the left-hand movement increased, the left M1 showed a gradual decrease in the deactivation. This data suggests a frequency-dependent increased involvement of the left M1 in ipsilateral hand control. By contrast, the right M1 showed more prominent deactivation as the frequency of the right-hand movement increased. This suggests that there is an increased transcallosal inhibition from the left M1 to the right M1, which overwhelms the right M1 activation during ipsilateral hand movement. These results demonstrate the dominance of the left M1 in both ipsilateral innervation and transcallosal inhibition in right-handed individuals.

Quantification of delayed oxygenation in ipsilateral primary motor cortex compared with contralateral side during a unimanual dominant-hand motor task using near-infrared spectroscopy

Using near-infrared spectroscopy (NIRS) techniques, it is possible to examine bilateral motor cortex oxygenation during a static motor task. Cortical activation was assumed to be reflected by increased oxygenation. The purpose of the present study was to examine the time course of oxygenation in the bilateral motor cortex during a low-intensity handgrip task. Six healthy, right-handed subjects participated in the study. The near-infrared spectroscopy probes positioned over the bilateral motor cortex were used to measure the cortical activation throughout a handgrip task carried out. The subjects performed a 3-min handgrip task with increasing intensity in a ramp-like manner [10–30% of the maximal voluntary contraction (MVC) at 6.67% MVC.min − 1 ]. Contralateral motor cortex oxygenation increased significantly from 100 to 180 s after the start of the motor task compared with the baseline value ( p < 0.05). Ipsilateral motor cortex oxygenation also increased significantly from 130 to 180 s after the start of the motor task ( p < 0.05). The onset of increase in oxyhemoglobin ([HbO 2]) and decrease in deoxyhemoglobin ([Hb]) in contralateral motor cortex area (M1) were significantly earlier than in ipsilateral M1 (respectively, p < 0.05). These results show that there is a delayed oxygenation in ipsilateral primary motor cortex area compared with contralateral side during a unimanual dominant-hand motor task.

Memory Formation in the Motor Cortex Ipsilateral to a Training Hand

Cortical reorganization within the primary motor cortex (M1) contralateral to a practicing hand has been extensively investigated. The extent to which the ipsilateral M1 participates in these plastic changes is not known. Here, we evaluated the influence of unilateral hand practice on the organization of the M1 ipsilateral and contralateral to the practicing hand in healthy human subjects. Index finger movements elicited by single-pulse transcranial magnetic stimulation (TMS) delivered to each M1 were evaluated before and after practice of unilateral voluntary index finger abduction motions. Practice increased the proportion and acceleration of TMS-evoked movements in the trained direction and the amplitude of motor-evoked potentials (MEPs) in the abduction agonist first dorsal interosseous (FDI) muscle in the practicing hand and decreased the proportion and acceleration of TMS-evoked abduction movements and MEP amplitudes in the abduction agonist FDI in the opposite resting hand. Our findings indicate that unilateral hand practice specifically weakened the representation of the practiced movement in the ipsilateral M1 to an extent proportional to the strengthening effect in the contralateral M1, a result that varied with the practicing hand's position. These results suggest a more prominent involvement of interacting bilateral motor networks in motor memory formation and probably acquisition of unimanual motor skills than previously thought.

Impairment of complex upper limb motor function in de novo Parkinson's disease

The aim of the present study was to evaluate complex upper limb motor function in newly diagnosed, untreated Parkinson's disease (PD) patients. Four different unimanual upper limb motor tasks were applied to 13 newly diagnosed, untreated PD patients and 13 age- and sex-matched controls. In a handwriting task, PD patients had significantly reduced sentence length and writing velocity, and decreasing letter height in the course of writing. Furthermore, PD patients performed an aiming task slower with than without target, and showed increased transposition in a pointing task. The results of this study extend previous observations of impaired complex upper limb movements to newly diagnosed, untreated PD patients.

Cortical networks underlying coordinated movements revealed by magnetoencephalographic beamforming

Abstract Event-related beamformer analyses was applied to magnetoencephalographic data from five subjects who performed synchronized and syncopated unimanual motor coordination tasks at rates ranging from 1.25 to 1.75 Hz. For syncopation, the stability of the coordination pattern decreased systematically with increasing movement rate. Averaged sensor data revealed the motor field (MF) and motor evoked fields (MEF) I and II. Additionally, we observed an early field (M0) at approximately 160 ms prior to peak flexion with polarity opposite to the MF. Beamformer analysis reproduced previous findings that showed the MF activity being generated mainly in precentral gyrus and the activity of the MEFs is distributed across multiple generators in pre- and post-central gyrus. For syncopation, additional areas of activation were observed during early M0 and late MEF II time periods which included premotor, frontal, cingulate, and SMA, with the premotor areas exhibiting a dependence on rate. These results provide evidence of the power of MEG beamforming for characterizing the properties of cortical neural activity at a high resolution in space and time.

Ipsilateral motor activation during unimanual and bimanual motor tasks

ObjectiveTo test for the presence and possible asymmetry of ipsilateral motor activation during unimanual and bimanual motor tasks. MethodsTwelve right-handed healthy subjects underwent motor evoked potential (MEP) measurement of one hand (target-hand) while the other hand (task-hand) performed different motor tasks. The target-hand was either at rest (first experiment) or performed a Perdue PegBoard task (second experiment). The task-hand was either at rest, performed a simultaneous pegboard task, or rotated a coin (second experiment). ResultsIn the first experiment, the motor task resulted in significant increase in MEP area in the target-hand, regardless which hand was the task-hand, with a greater increase when the left hand was the task-hand. In the second experiment, ipsilateral motor activation was not present for either hand, however, when the right hand was the task-hand, performance of continuous coin rotation by the right hand resulted in a significant decrease in the MEP area of the left hand. ConclusionsHemispheric asymmetry and task-dependence of ipsilateral motor cortex activation supports the postulate that motor activity may start bilaterally with subsequent interhemispheric inhibition. Furthermore, in right-handers, the left motor cortex is either more active in ipsilateral hand movements or exerts more effective inhibitory control over the right motor cortex than vice versa. SignificanceWe suggest that hemispheric asymmetry in ipsilateral motor control is a factor in determining motor dominance in right-handed individuals.

Surface electromyography shows increased mirroring in Parkinson's disease patients without overt mirror movements

Patients with Parkinson's disease (PD) may present mirror movements (MM). Transcranial magnetic stimulation data indicate that these movements reflect an abnormal enhancement of the "physiological mirroring" that can be observed in healthy adults during complex and effortful tasks. It was hypothesized that, in PD, enhanced mirroring is caused by a failure of basal ganglia output to support the cortical network that is responsible for the execution of strictly unimanual movements. If so, it is likely that subtle alterations of voluntary unimanual motor control are also present in PD patients without overt MM. We tested this hypothesis by using surface electromyographic (EMG) techniques in 12 mildly to moderately affected PD patients without overt MM, and in 2 control groups (12 age-matched and 10 young healthy volunteers). Subjects performed unilateral phasic thumb abduction during a sustained tonic contraction of the opposite abductor pollicis brevis. All patients were tested on dopaminergic therapy. On a separate day, 7 of 12 patients were re-tested after withdrawal of medication. During this task, involuntary mirror-like increase in surface EMG of the tonically abducting thumb was significantly larger in PD patients than in age-matched or young healthy volunteers. Off therapy, mirroring was slightly greater than on medication, although this difference was not significant. Our findings suggest that dysfunction of unimanual motor control is a general feature of PD. It is likely that this deficient movement lateralization contributes to an impairment of nonsymmetrical bimanual movements in PD.

Effects of aging and hormonal status on bimanual motor coordination in the rhesus monkey

Studies of age-related changes in motor function in nonhuman primates have been based exclusively on unimanual motor tasks. In this study, we examined whether aging affects bimanual motor coordination in the monkey model. In addition, we compared performance of ovariectomized and intact females on the task, to examine whether estrogen deficiency impairs motor function. The task required 29 rhesus monkeys (6–26 years old) to extract a maximum of 15 raisins from a testing hole-board. While the task could most efficiently be performed with two hands, other motor strategies were possible. The number of raisins extracted per minute was measured in each of eight sessions, the first and last of which were videotaped for analysis of motor patterns. The number of raisins retrieved per minute declined significantly with age. All monkeys improved with practice, but aged monkeys improved more slowly than young ones. The proportion of bimanual actions tended to increase between the first and the last sessions but was not significantly different between young and aged monkeys. Hormonal status did not affect performance. Finally, performance on the bimanual task was significantly correlated with performance on a previously administered unimanual motor test emphasizing speed, suggesting that age-related motor slowing may explain deficits in both tasks.