Distal Movements Research Articles

Effects of muscimol inactivation of the cerebellar nuclei on precision grip.

A single monkey was trained to perform a grasp, lift, and hold task in which a stationary hand- held object was sometimes subjected to brief, predictable force-pulse perturbations. The displacement, grip, and lifting forces were measured as well the three-dimensional forces and torques to quantify specific motor deficits after reversible inactivation of the cerebellar nuclei. A prior single-cell recording study in the same monkey provided the stereotaxic coordinates used to guide intranuclear injections of muscimol. In total, 34 penetrations were performed at 28 different loci throughout the cerebellar nuclei. On each penetration, two 1.0-microl injections of 5 microg/microl muscimol, were made 1.0 mm apart either within the nuclei or in the white matter just lateral or posterior to the dentate nucleus. Injections in the region corresponding to the anterior interpositus nucleus produced pronounced dynamic tremor and dysmetric movements of the ipsilateral arm when the animal performed unrestrained reaching and grasping movements. In contrast, no relatively short-latency (15-20 min.) deficits were observed after injection in the dentate nucleus, although some effects were observed after several hours. When tested in a primate chair with the forearm supported and restrained at the wrist and elbow, the monkey performed the lift and hold task without tremor or dysmetria. However, with the restraint removed, the forces and torques applied to the manipulandum were poorly controlled and erratic. The monkey's arm was ataxic and a 5-Hz intention tremor was clearly visible. In addition, the animal was generally unable to compensate for the predictable perturbations and the anticipatory grip force increases were absent. However, overall the results suggest that reversible cerebellar nuclear inactivation with muscimol has little effect on isolated distal movements of the wrist and fingers.

Role of the medial parieto-occipital cortex in the control of reaching and grasping movements.

The medial parieto-occipital cortex is a central node in the dorsomedial visual stream. Recent physiological studies in the macaque monkey have demonstrated that the medial parieto-occipital cortex contains two areas, the visual area V6 and the visuomotor area V6A. Area V6 is a retinotopically organized visual area that receives form and motion information directly from V1 and is heavily connected with the other areas of the dorsal visual stream, including V6A. Area V6A is a bimodal visual/somatosensory area that elaborates visual information such as form, motion and space suitable for the control of both reaching and grasping movements. Somatosensory and skeletomotor activities in V6A affect the upper limbs and involve both the transport phase of reaching and grasping movements. Finally, V6A is strongly and reciprocally connected with the dorsal premotor cortex controlling arm movements. The picture emerging from these data is that the medial parieto-occipital cortex is well equipped to control both proximal and distal movements in the online visuomotor guidance of prehension. In agreement with this view, selective V6A lesions in monkey produce misreaching and misgrasping with the arm contralateral to the lesion in visually guided movements. These deficits are similar to those observed in optic ataxia patients and suggest that human and monkey superior parietal lobules are homologous structures, and that optic ataxia syndrome is the result of the lesion of a 'human' area V6A.

Somatotopic organization of the lateral part of area F2 (dorsal premotor cortex) of the macaque monkey.

The somatotopy of the lateral part of dorsal premotor area F2 has been studied by means of intracortical microstimulation and single neuron recording. The results show that most of this sector of F2 is excitable with low-intensity currents (3-40 microA) and that intracortical microstimulation evokes forelimb and trunk movements. Both proximal and distal forelimb movements are evoked in similar percentages. The proximal and distal forelimb representations partially overlap. However, proximal movements tend to be located more medially (laterally to the superior precentral dimple), whereas distal movements tend to be located more laterally (medially to the spur of the arcuate sulcus). The somatotopic organization demonstrated with microstimulation is confirmed by the similar somatotopic organization of active movements and of somatosensory properties revealed by single-neuron recording. The excitability and somatotopic organization of the lateral part of area F2 are discussed in relation to previous electrophysiological and anatomical findings. The involvement of the distal forelimb representation of area F2 in programming and controlling reaching to grasp movements is suggested.

Pantomime to visual presentation of objects: left hand dyspraxia in patients with complete callosotomy.

Investigations of left hand praxis in imitation and object use in patients with callosal disconnection have yielded divergent results, inducing a debate between two theoretical positions. Whereas Liepmann suggested that the left hemisphere is motor dominant, others maintain that both hemispheres have equal motor competences and propose that left hand apraxia in patients with callosal disconnection is secondary to left hemispheric specialization for language or other task modalities. The present study aims to gain further insight into the motor competence of the right hemisphere by investigating pantomime of object use in split-brain patients. Three patients with complete callosotomy and, as control groups, five patients with partial callosotomy and nine healthy subjects were examined for their ability to pantomime object use to visual object presentation and demonstrate object manipulation. In each condition, 11 objects were presented to the subjects who pantomimed or demonstrated the object use with either hand. In addition, six object pairs were presented to test bimanual coordination. Two independent raters evaluated the videotaped movement demonstrations. While object use demonstrations were perfect in all three groups, the split-brain patients displayed apraxic errors only with their left hands in the pantomime condition. The movement analysis of concept and execution errors included the examination of ipsilateral versus contralateral motor control. As the right hand/left hemisphere performances demonstrated retrieval of the correct movement concepts, concept errors by the left hand were taken as evidence for right hemisphere control. Several types of execution errors reflected a lack of distal motor control indicating the use of ipsilateral pathways. While one split-brain patient controlled his left hand predominantly by ipsilateral pathways in the pantomime condition, the error profile in the other two split-brain patients suggested that the right hemisphere controlled their left hands. In the object use condition, in all three split-brain patients fine-graded distal movements in the left hand indicated right hemispheric control. Our data show left hand apraxia in split-brain patients is not limited to verbal commands, but also occurs in pantomime to visual presentation of objects. As the demonstration with object in hand was unimpaired in either hand, both hemispheres must contain movement concepts for object use. However, the disconnected right hemisphere is impaired in retrieving the movement concept in response to visual object presentation, presumably because of a deficit in associating perceptual object representation with the movement concepts.

Complex partial seizures of frontal lobe onset statistical analysis of ictal semiology

Objective: To identify the ictal semiology of complex partial seizures originating from the frontal lobe (FLCPS) and mesial temporal lobe (MTLE) in patients who became seizure free after surgery. Methods: We analysed 149 seizures from 42 patients, 28 with MTLE (75 seizures) and 14 with FLCPS (74 seizures) seizure free for at least 1 year after surgery. Fifty-eight symptoms and signs were looked for in every seizure and their time of onset and ending noted. Statistical analysis was then used to define the frequency, time of onset and cluster analysis of these symptoms/signs. Results: Epigastric aura was more frequent in MTLE while an aura of a general body sensation or indescribable feeling occurred only in FLCPS. Alimentary automatisms were more common and occurred earlier in MTLE ( P<0.001). Perseverative automatisms, retching and vomiting occurred exclusively in MTLE while bicycling movements occurred only in FLCPS. Abdominal, psychic or olfactory aura followed by behavioural arrest, alimentary automatisms, repetitive distal upper extremity movements, complete loss of consciousness, looking around and whole body movements were typical of MTLE. Repetitive coarse upper extremity movements, complete loss of consciousness, complex motor and hypermotor activity were typical of FLCPS. Conclusion: The earliest symptoms and signs as well as their order of appearance allow one to distinguish between complex partial seizures arising from the frontal lobe and mesial temporal lobe.

Cervical cord tethering due to split cord malformation at the cervico‐dorsal junction presenting with self‐mutilation of the fingers

An unusual case of cervical spinal cord tethering with diplomyelia is described. A 12‐month old female presented with self‐mutilation of the fingers due to sensory loss in the hands, absent reflexes, poor muscle tone, and reduced distal upper‐limb movements. There was a deep skin dimple overlying the T1 spinous process. Imaging showed angulation of the lower cervical cord and an operation revealed a low cervical meningocele and a split cord malformation with tethering of one half of the cord; the cord was untethered. In this report the literature is reviewed.

Shift from hypermetria to hypometria in multiple system atrophy: Analysis of distal and proximal movements

Dysmetria is a classical sign which designates the overshoot, also called hypermetria, and the undershoot, or hypometria, when the patient attempts to reach rapidly an aimed target. Dysmetria is typically observed in patients presenting a cerebellar dysfunction. Dysmetria of distal movements is associated with an imbalance between the timing and/or the intensity of agonist and antagonist EMG activities. So far, 1. there is only one description in human of a shift from hypermetria to hypometria for fast goal-directed single-joint movements during an aberrant recovery following a cerebellar infarction, and 2. such a shift has not been described for proximal movements. We report a patient presenting a multiple system atrophy (MSA). Initially, he exhibited a marked cerebellar syndrome. Fast wrist flexions and fast upper limb reaches in the sagittal plane were hypermetric. The distal hypermetria was associated with a delayed onset latency of the antagonist EMG activity and reduced intensities of both the agonist and the antagonist EMG activities. The proximal hypermetria was associated with a defect in the phasic spatial tuning of the EMG activities. He developed progressively severe extra-pyramidal signs. Distal hypermetria turned into hypometria, as a result of a decrease in the intensity of the agonist muscle. Proximal hypermetria turned into hypometria, as a result of the loss of directional preference of the EMG activities in proximal muscles. MSA is the second human model of a shift from hypermetria to hypometria. [Neurol Res 2002; 24: 249-258]

Interactive effect of cytochrome P450 17α-hydroxylase and dopamine D3 receptor gene polymorphisms on abnormal involuntary movements in chronic schizophrenia

Background: Tardive dyskinesia is a chronic adverse effect of anti psychotic drugs, where association with a polymorphic site in the dopamine D3 receptor gene has been previously reported. Cytochrome P 450 17α-hydroxylase activity has been implicated with modulation of central dopamine release as well as neuroprotection. We investigated the association of a T →C variation in the cytochrome P 450 17α-hydroxylase gene with tardive dyskinesia in patients with chronic schizophrenia. Methods: Cytochrome P 450 17 allele and genotype frequencies were compared between matched schizophrenia patients with ( n = 55) or without tardive dyskinesia ( n = 58). Interactive effects of cytochrome P 450 17α-hydroxylase with the dopamine D3 Ser9Gly polymorphism on abnormal involuntary movements were examined. Results: There was no difference in cytochrome P 450 17α-hydroxylase genotype distribution between patients with and without tardive dyskinesia; however, patients carrying the cytochrome P 450 17α-hydroxylase A2-A2 genotype and the dopamine D3gly allele had the highest orofacial ( p < .04), distal ( p < .05), and incapacitation ( p < .04) scores on the Abnormal Involuntary Movements Scale. Conclusions: Schizophrenia patients who carry the dopamine D3gly allele and the cytochrome P 450 17α-hydroxylase A2-A2 genotype may be more likely to develop abnormal orofoacial and distal involuntary movements and to be incapacitated by these movements when chronically exposed to classical antipsychotic drugs.

Electrophysiological confirmation of the zona incerta as a target for surgical treatment of disabling involuntary arm movements in multiple sclerosis: use of local field potentials

Lesioning or chronic deep brain stimulation (DBS) of the nucleus ventralis intermedius results in abolition of tremor in the contralateral limbs in Parkinson's disease (PD) and also in essential tremor. Recently, chronic DBS of the subthalamic nucleus has also proved to be very effective in reducing contralateral limb tremor in PD. These targets have been less effective in controlling the complex limb tremor often seen in multiple sclerosis (MS). Consequently, other targets have been sought in cases of MS with tremor. We describe a patient with MS with disabling proximal and distal involuntary arm movements in whom we were able to obtain sustained control of contralateral arm tremor and achieve functional improvement of the affected arm by chronic DBS of the region of the zona incerta. We also highlight the important role played by local field potentials recorded from the brain, with simultaneous recording of corresponding EMGs, in target localisation.

Effects of hyperventilation on fast goal-directed limb movements in spinocerebellar ataxia type 6.

It has been shown previously that hyperventilation modifies the features of the nystagmus in cerebellar patients (Walker and Zee, 1999). It has been hypothesized that hyperventilation influences the oculomotor control through a metabolic effect on cerebellar calcium channels, which play a critical role in the firing behaviour of neuronal populations in the cerebellum. This hypothesis has been tested here by analysing fast goal-directed limb movements before and after hyperventilation in spinocerebellar ataxia type 6 (SCA-6), a disease associated with a polyglutamine expansion in the alpha 1-A voltage-dependent calcium channel. Cerebellar hypermetria associated with fast distal single-joint movements was found to be increased following hyperventilation in patients presenting SCA-6 but remained unchanged in patients with idiopathic late-onset cerebellar degeneration (ILOCA). This is a new provocative test to enhance distal dysmetria in SCA-6. The present results strengthen the hypothesis of Walker and Zee. It is suggested that hyperventilation enhances the defective calcium transfers in SCA-6, resulting in an impairment of the calcium influx in particular into Purkinje cells involved in the control of fast goal-directed voluntary movements.

Different Ipsilateral Representations for Distal and Proximal Movements in the Sensorimotor Cortex: Activation and Deactivation Patterns

Each hemisphere is known to be also involved in controlling the ipsilateral arm, but with an asymmetry favoring the dominant hemisphere. However, the relative role of primary and secondary motor areas in ipsilateral control is not well defined. We used whole brain functional magnetic resonance imaging in healthy human subjects to differentiate between contributions from primary and secondary areas during discrete unilateral distal finger and proximal shoulder movements. It was found that ipsilateral distal movements activated secondary areas only, while sparing or even significantly deactivating the primary sensorimotor cortex. Ipsilateral proximal movements substantially activated both SM1 and secondary areas. A newly defined small territory within the precentral gyrus, extending from the premotor cortex and intruding toward SM1, showed an activation pattern corresponding to secondary motor areas. Finally, the effects of hemispheric dominance were confirmed, but attributed exclusively to secondary areas. These new imaging findings agree well with functional requirements as well as established anatomical and neurophysiological data.

Somatotopic arrangement and corticocortical inputs of the hindlimb region of the primary motor cortex in the macaque monkey.

Using Japanese monkeys, we examined the somatotopic organization of the hindlimb region of the primary motor cortex (MI) with intracortical microstimulation. In the hindlimb region of the MI, areas representing distal movements (digits and ankle joints) were basically surrounded by those representing proximal movements (knee and hip joints). Thus, the hindlimb region of the MI has a nested or horseshoe-like somatotopic representation. We then examined the topographic organization of corticocortical projections to the hindlimb region of the MI by the retrograde double-labeling technique: one monkey received paired injections of Fast blue (FB) and Diamidino yellow (DY) into hindlimb or forelimb representation of the MI, respectively, while two monkeys received those of FB and DY into proximal or distal representation of the hindlimb region of the MI, respectively. The neurons projecting to the hindlimb region of the MI were located in cortical areas largely separate from those projecting to the forelimb region of the MI. On the other hand, we found a substantial overlap of corticocortical neurons projecting to the proximal and distal parts of the hindlimb region of the MI in the dorsal division of the premotor cortex and the cingulate motor areas.

Early neurological signs in preterm infants with unilateral intraparenchymal echodensity.

The aim of the study was to document the early developmental course of neurological signs in a group of preterm infants at risk for hemiplegia due to unilateral intraparenchymal echodensity (UIPE). Sixteen preterm infants with UIPE and sixteen controls were given serial neurological examinations, according to the protocols currently adopted in the different NICUs of the project. Moreover, the quality assessment of their general movements (GMs) was assessed subsequently from videotapes, from birth until around four months postterm. At two years, 12 of the UIPE infants showed hemiplegia and one suffered from asymmetrical diplegia. The findings of the traditional neurological examination were abnormal for the large majority of the UIPE infants, although normal findings were also recorded in some cases, especially during the preterm period. Asymmetries were found after term age in nine UIPE and in two control infants. From the first observation onwards, all infants with UIPE showed bilaterally abnormal GMs and in those with unfavourable outcome fidgety movements (FMs) were absent. At the FMs period (9-16 weeks postterm), all infants with subsequent hemiplegia showed asymmetry of distal segmental movements which were reduced or absent on the side contralateral to the lesion. Unilateral brain lesions induce clear neurological signs and abnormal GMs in particular, although these abnormalities are not initially asymmetrical. A reduction of segmental movements on one side of the body during the third month postterm is highly predictive of hemiplegia.

Human motor development and hand laterality: a kinematic analysis of drawing movements

This study examines the developmental profiles of basic ‘open-loop’ drawing movements on the non-dominant hand (ND) in comparison with the dominant hand (D). Fifty-three right-handed children aged 7–14 years and 15 adults aged 27–43 years were examined. Each subject drew lines and circles of different sizes at maximum velocity with a pressure-sensitive pen on a computer graphics tablet. Small lines were drawn at 90° to the axis of the forearm (lines using wrist movements (LWM)) and along the axis of the forearm (lines using elbow movements (LEM)). Larger lines were drawn at 90° to the axis of the forearm (LEM). At both extremities, the movement frequencies of the proximally generated drawing movements increased in a parallel fashion at different levels. In LWM, the right-left-differences (RLD) were high in 7- to 8-year-old children; until puberty, the ND hand reached almost the performance of the D hand. In contrast, the RLD of the LFM increased at the same time. As adulthood approaches, frequencies of all drawings increased further while the LWM on the ND side remained stable. In adults, there were similar RLD for all line drawings involving predominantly flexion and extension movements. When drawing circles, the RLD were highest, though stable in all age groups. Hand laterality of pen use changes over time; these changes are dependent on complexity (combined/sequential cf. flexion-extension muscle activation) and on topography (proximal cf. distal movements). Distinct developmental profiles of motoneuronal populations of the cortex may be responsible for the distinct hand laterality effects and the decreasing variability of motor patterns. The drawing abilities and developmental changes on the untrained ND hand indicate that effector-specific practice plays a minor role.

The Royal London Space Planning: An integration of space analysis and treatment planning: Part I: Assessing the space required to meet treatment objectives

The Royal London Space Planning process has evolved since 1985 to ensure a disciplined approach to diagnosis and treatment planning and to provide a record to justify treatment decisions for professional accountability. The analysis takes into consideration most aspects of a given malocclusion and aims to quantify the space required in each dental arch to attain the treatment objectives. Space planning also helps determine whether the objectives are likely to be attainable and helps in the planning of treatment mechanics and the control of anchorage. The process of analysis is divided into 2 sections. The first part consists of assessing the original malocclusion according to various component parts, any of which may have an effect on space if altered during treatment. These components are crowding and spacing, occlusal curves, arch width, anteroposterior position of labial segments, mesiodistal angulation, and incisor inclination. The second part of the analysis, which will be published in a separate article, deals with the effect of treatment procedures, such as extractions, tooth-size modifications, distal or mesial molar movements, as well as natural growth, on the space required. Space planning should be regarded only as a useful guide, as many areas of orthodontics—including growth, biological response, and patient compliance-cannot be controlled with total accuracy. (Am J Orthod Dentofacial Orthop 2000;118:448-55).

Effects of Repetitive Motor Training on Movement Representations in Adult Squirrel Monkeys: Role of Use versus Learning

Current evidence indicates that repetitive motor behavior during motor learning paradigms can produce changes in representational organization in motor cortex. In a previous study, we trained adult squirrel monkeys on a repetitive motor task that required the retrieval of food pellets from a small-diameter well. It was found that training produced consistent task-related changes in movement representations in primary motor cortex (M1) in conjunction with the acquisition of a new motor skill. In the present study, we trained adult squirrel monkeys on a similar motor task that required pellet retrievals from a much larger diameter well. This large-well retrieval task was designed to produce repetitive use of a limited set of distal forelimb movements in the absence of motor skill acquisition. Motor activity levels, estimated by the total number of finger flexions performed during training, were matched between the two training groups. This experiment was intended to evaluate whether simple, repetitive motor activity alone is sufficient to produce representa tional plasticity in cortical motor maps. Detailed analysis of the motor behavior of the monkeys indicates that their retrieval behavior was highly successful and stereotypical throughout the training period, suggesting that no new motor skills were learned during the performance of the large-well retrieval task. Comparisons between pretraining and posttraining maps of M1 movement representations re vealed no task-related changes in the cortical area devoted to individual distal forelimb movement representations. We conclude that repetitive motor activity alone does not produce functional reorganization of cortical maps. Instead, we propose that motor skill acquisition, or motor learning, is a prerequisite factor in driving representational plasticity in M1.

Molar distalization with the Herbst appliance

This article reviews the dental effects of the Herbst appliance as well as itslong-term effects on the dentition. The Herbst appliance exhibits a pronounced high-pull headgear effect on the maxillary molars. Without retention, the molars tend to return to their former anteroposterior positions after the removal of the appliance. These distal movements of the maxillary molars are favorable in Class II correction. Reciprocal mesial movements of the mandibular dentition, however, may not be desirable in many instances. Even though partial recovery occurs after Herbst therapy, treatment effects can persist in the mandibular arch. The latter effect can be beneficial to those patients who have initial retroclined mandibular incisors, but unfavorable in those patients with proclined lower incisors at the beginning of treatment.

Oscillatory cortical activity and movement-related potentials in proximal and distal movements

Objectives: Event-related desynchronization (ERD) of α- and β-rhythms, the post-movement β-synchronization and the cortical movement-related potentials were analyzed in distal (finger) and proximal (shoulder) movements. Methods: EEG was recorded in 7 healthy right-handed men using a 59-channel whole-head EEG system while subjects performed self-paced movements. Results: The amplitude of the Bereitschaftspotential (BP) was greater over the central midline area and smaller over the contralateral sensorimotor hand area in shoulder than in finger movements. The maximal α- and β-ERD was localized at parietal electrodes in shoulder movements and over the left and right sensorimotor hand area in finger movements. The post-movement β-ERS was greater in shoulder than in finger movements, especially at the electrode located 3.5 cm left of the central midline electrode. A significant correlation between the slope of the terminal portion of the BP (negative slope) and amplitude of the post-movement β-synchronization was observed in shoulder but not in finger movements. Conclusions: Enhancement of BP over the central midline electrode suggests increased activation of the supplementary motor area in proximal movements. The spatial distribution of the α- and β-ERD and of the post-movement β-ERS shows topographic differences which may refer to the somatotopic organization of the primary sensorimotor cortex with shoulder representation medial to hand and fingers. The correlation between the negative slope and the post-movement β-ERS in proximal movements supports the view that the brief post-movement inhibition over the motor cortical area is related to the pre-movement activation of that area.

Management of anteroposterior dental movements

Management of the anteroposterior dimension is one of the most common problems encountered in orthodontic treatment. Numerous methods are available to treat the anteroposterior discrepancy depending on the treatment objectives and the available growth potential. Some situations may require a dental correction such as maxillary molar derotation or distal movements of both the upper and lower molars. If additional arch length is required, the extraction of permanent teeth may serve as an effective treatment modality as long as the anchorage requirements are considered. Other instances may necessitate skeletal correction via growth modification ie, maintaining the maxilla anteroposteriorly during growth. Regardless of the treatment mechanics used, it is important to understand how these different methods can affect the amount of arch length gained with respect to the treatment objectives for incisor and molar position. Once the objectives for incisor and molar position are determined, then the appropriate mechanotherapy can be used.

Impairments in prehension produced by early postnatal sensory motor cortex activity blockade.

This study examined the effects of blocking neural activity in sensory motor cortex during early postnatal development on prehension. We infused muscimol, either unilaterally or bilaterally, into the sensory motor cortex of cats to block activity continuously between postnatal weeks 3-7. After stopping infusion, we trained animals to reach and grasp a cube of meat and tested behavior thereafter. Animals that had not received muscimol infusion (unilateral saline infusion; age-matched) reached for the meat accurately with small end-point errors. They grasped the meat using coordinated digit flexion followed by forearm supination on 82.7% of trials. Performance using either limb did not differ significantly. In animals receiving unilateral muscimol infusion, reaching and grasping using the limb ipsilateral to the infusion were similar to controls. The limb contralateral to infusion showed significant increases in systematic and variable reaching end-point errors, often requiring subsequent corrective movements to contact the meat. Grasping occurred on only 14.8% of trials, replaced on most trials by raking without distal movements. Compensatory adjustments in reach length and angle, to maintain end-point accuracy as movements were started from a more lateral position, were less effective using the contralateral limb than ipsilateral limb. With bilateral inactivations, the form of reaching and grasping impairments was identical to that produced by unilateral inactivation, but the magnitude of the reaching impairments was less. We discuss these results in terms of the differential effects of unilateral and bilateral inactivation on corticospinal tract development. We also investigated the degree to which these prehension impairments after unilateral blockade reflect control by each hemisphere. In animals that had received unilateral blockade between postnatal weeks (PWs) 3 and 7, we silenced on-going activity (after PW 11) during task performance using continuous muscimol infusion. We inactivated the right (previously active) and then the left (previously silenced) sensory motor cortex. Inactivation of the ipsilateral (right) sensory motor cortex produced a further increase in systematic error and less frequent normal grasping. Reinactivation of the contralateral (left) cortex produced larger increases in reaching and grasping impairments than those produced by ipsilateral inactivation. This suggests that the impaired limb receives bilateral sensory motor cortex control but that control by the contralateral (initially silenced) cortex predominates. Our data are consistent with the hypothesis that the normal development of skilled motor behavior requires activity in sensory motor cortex during early postnatal life.