ASSOCIATED MOVEMENTS IN NORMAL AND PHYSICALLY HANDICAPPED CHILDREN

The psychophysiology of "covert" goal-directed behavior

Covert behavior is defined as behavior that is not directly visible and is thus comparable to a type of behavioral silence that requires modern psychophysiological techniques to reveal. Goal-directed behavior is teleologically purposive. Fundamentally, there are two approaches to accounting for purposeful behavior. One is the cybernetic approach, which views behavior as homeostatic and largely reflexive. The other one views behavior as a cognitive process that involves an interaction between neural events representing the previous experience, the present state of the individual, and the occurrence of particular features in the environment. This review, based on published data, presents a non-invasive psychophysiological method for investigating the electrical brain activity associated with those "silent" behaviors such as intention, evaluation of results, and memorization. Movement-related potentials (MRPs) are ideal for studying these processes. The MRPs are recorded during the execution of the skilled performance task (SPT). This task requires the execution of fast ballistic movements with the thumbs of both hands, learning a precise and short time interval between the two thumb presses, and scoring the highest number of target performances. The subject receives real-time feedback about the results of his performance. The MRPs associated with this task and present during covert behavior are the Bereitschaftspotential (BP) present before the onset of movement and the Skilled Performance Positivity (SPP) after movement, which coincides with the subject's awareness of the success or failure of his performance. These potentials show a maturational trend, reaching the adult form around the age of 10 when formal and abstract thinking progress. SPT and MRPs are particularly suitable to study neurodevelopmental disorders. Children with developmental dyslexia show abnormal MRPs, both in latency and amplitude, in different brain areas.

Attention Deficits Influence the Development of Motor Abnormalities in High Functioning Autism

Early attentional dysfunction is one of the most consistent findings in autism spectrum disorder (ASD), including the high functioning autism (HFA). There are no studies that assess how the atypical attentional processes affect the motor functioning in HFA. In this study, we evaluated attentional and motor functioning in a sample of 15 drug-naive patients with HFA and 15 healthy children (HC), and possible link between attentional dysfunction and motor impairment in HFA. Compared to HC, HFA group was seriously impaired in a considerable number of attentional processes and showed a greater number of motor abnormalities. Significant correlations between attention deficits and motor abnormalities were observed in HFA group. These preliminary findings suggest that deficit of attentional processes can be implied in motor abnormalities in HFA.

Contra-Lateral Unintended Upper Arm Movement during Unimanual Tasks in Children with Cerebral Palsy

PURPOSE

To characterize associated reactions (ARs) in the contralateral arm across multiple muscles during unimanual tasks and to identify factors related to ARs in children with cerebral palsy (CP).

MATERIALS AND METHODS

This was a prospective, cross-sectional study of 35 children with CP. The extent of ARs of the contra-lateral, non-task hand was assessed while performing three unimanual tasks (opening and clenching the fist, a finger opposition task, and tapping fingers). The occurrence of ARs in each trial was evaluated separately for each task using a four-point scale (total scores ranged from 0 to 12). Surface electromyography (SEMG) was used to measure the firing activity of the muscles of the opposite arm during the task. The Manual Ability Classification System and Melbourne Assessment 2 (MA-2) were used to evaluate upper limb function.

RESULTS

AR scores were higher in the more-affected limb than in the less-affected limb. SEMG data on the non-task hand showed motor overflow up to the elbow muscles in the more-affected limb. Root mean square ratios of EMG signals were significantly higher in children with ARs than in children without ARs. Multiple regression analysis showed both age and MA-2 to be significant factors related to ARs in the more-affected limb.

CONCLUSION

Children with visible ARs showed motor overflow in the non-task limb during unimanual hand tasks. Age and upper limb function were significantly related to the extent of ARs in the more-affected limb of children with CP.

Muscle Activation Patterns During Movement Attempts in Children With Acquired Spinal Cord Injury: Neurophysiological Assessment of Residual Motor Function Below the Level of Lesion

Introduction: Characterization of residual neuromotor capacity after spinal cord injury (SCI) is challenging. The current gold standard for measurement of sensorimotor function after SCI, the International Society for Neurological Classification of Spinal Cord Injury (ISNCSCI) exam, seeks to determine isolated intentional muscle activation, however many individuals with SCI exhibit intentional movements and muscle activation patterns which are not confined to specific joint or muscle. Further, isolated muscle activation is a feature of the neuromuscular system that emerges during development, and thus may not be an appropriate measurement standard for children younger than 6.

Methods: We utilized neurophysiological assessment methodology, long studied in adult SCI populations, to evaluate residual neuromotor capacity in 24 children with SCI, as well as 19 typically developing (TD) children. Surface electromyography (EMG) signals were recorded from 11 muscles bilaterally, representing spinal motor output from all regions (i.e., cervical, thoracic, and lumbosacral), during standardized movement attempts. EMG records were subjectively analyzed based on spatiotemporal muscle activation characteristics, while the voluntary response index (VRI) was utilized for objective analysis of unilateral leg movement tasks.

Results: Evidence of intentional leg muscle activation below the level of lesion was found in 11/24 children with SCI, and was classified based on activation pattern. Trace activation, bilateral (generalized) activation, and unilateral or isolated activation occurred in 32, 49, and 8% of movement tasks, respectively. Similarly, VRI analyses objectively identified significant differences between TD and SCI children in both magnitude (p < 0.01) and similarity index (p < 0.05) for all unilateral leg movement tasks. Activation of the erector spinae muscles, recorded at the T10–T12 vertebral level, was observed in all children with SCI, regardless of injury level or severity.

Conclusions: Residual descending influence on spinal motor circuits may be present after SCI in children. Assessment of multi-muscle activation patterns during intentional movement attempts can provide objective evidence of the presence and extent of such residual muscle activation, and may provide an indicator of motor recovery potential following injury. The presence of residual intentional muscle activation has important implications for rehabilitation following pediatric-onset SCI.

Unilateral movement preparation causes task-specific modulation of TMS responses in the passive, opposite limb

KEY POINTS

Activity in the primary motor cortices of both hemispheres increases during unilateral movement preparation, but the functional role of ipsilateral motor cortex activity is unknown. Ipsilateral motor cortical activity could represent subliminal 'motor planning' for the passive limb. Alternatively, it could represent the state of the active limb, to support coordination between the limbs should a bimanual movement be required. Here we assessed how preparation of forces toward different directions, with the left wrist, alters evoked responses to transcranial magnetic stimulation of left motor cortex. Preparation of a unilateral movement caused excitability increases in ipsilateral motor cortex that reflected forces produced with the active limb in an intrinsic (body-centred), rather than an extrinsic (world-centred), coordinate system. These results suggest that ipsilateral motor cortical activity prior to unilateral action reflects the state of the active limb, rather than subliminal motor planning for the passive limb.

ABSTRACT

Corticospinal excitability is modulated for muscles on both sides of the body during unilateral movement preparation. For the effector, there is a progressive increase in excitability, and a shift in direction of muscle twitches evoked by transcranial magnetic stimulation (TMS) toward the impending movement. By contrast, the directional characteristics of excitability changes in the opposite (passive) limb have not been fully characterized. Here we assessed how preparation of voluntary forces towards four spatially distinct visual targets with the left wrist alters muscle twitches and motor-evoked potentials (MEPs) elicited by TMS of left motor cortex. MEPs were facilitated significantly more in muscles homologous to agonist rather than antagonist muscles in the active limb, from 120 ms prior to voluntary EMG onset. Thus, unilateral motor preparation has a directionally specific influence on pathways projecting to the opposite limb that corresponds to the active muscles rather than the direction of movement in space. The directions of TMS-evoked twitches also deviated toward the impending force direction of the active limb, according to muscle-based coordinates, following the onset of voluntary EMG. The data indicate that preparation of a unilateral movement increases task-dependent excitability in ipsilateral motor cortex, or its downstream projections, that reflects the forces applied by the active limb in an intrinsic (body-centred), rather than an extrinsic (world-centred), coordinate system. The results suggest that ipsilateral motor cortical activity prior to unilateral action reflects the state of the active limb, rather than subliminal motor planning for the passive limb.

Comorbidity of ADHD and High-functioning Autism: A Pilot Study on the Utility of the Overflow Movements Measure

OBJECTIVES

Children with attention-deficit/hyperactivity disorder (ADHD) and high-functioning autism (HFA) commonly show neurological soft signs (NSS) and impairment in executive functioning (EF). Many children with HFA may experience ADHD-like symptoms, and the 2 disorders may be comorbid. Evaluating NSS and EF in drug-naive subjects with ADHD, HFA, and ADHD+HFA compared with healthy children may be critical in understanding and differentiating the biological substrates and cognitive phenotypes associated with these disorders. The goal of this study was to evaluate possible differences among these groups in motor and EF and the effects of comorbidity.

METHODS

Thirty-eight drug-naive patients (13 with ADHD, 13 with HFA, 12 with ADHD+HFA) and 13 healthy controls (HC) were evaluated on measures of planning, verbal working memory, and response inhibition. Evaluation of NSS involved 3 primary variables: overflow movements (OM), dysrhythmia, and speed of timed activities.

RESULTS

The group with ADHD and the group with HFA both showed impairment on measures of planning, response inhibition, and verbal working memory compared with the HC group. Moreover, the group with ADHD showed a greater number of NSS compared with the HC group, whereas the group with HFA showed greater dysrhythmia and slowness compared with the HC group. The group with ADHD+HFA showed deficits of planning and response inhibition and a greater number of NSS compared with the HC group. The group with ADHD+HFA showed greater impairment of planning compared with the other clinical groups and greater dysrhythmia compared with the group with ADHD.

CONCLUSION

According to our data, the OM measure revealed a gradient in which ADHD was at one extreme (more OM) and HFA at the other extreme (less OM), whereas ADHD+HFA showed a number of OM that fell in the middle between the numbers for the ADHD and HFA groups.

Developmental changes in lateralized inhibition of symmetric movements in children with and without Developmental Coordination Disorder

The present study investigates developmental changes in selective inhibition of symmetric movements with a lateralized switching task from bimanual to unimanual tapping in typically developing (TD) children and with Developmental Coordination Disorder (DCD) from 7 to 10 years old. Twelve right-handed TD children and twelve gender-matched children with DCD and probable DCD produce a motor switching task in which they have (1) to synchronize with the beat of an auditory metronome to produce bimanual symmetrical tapping and (2) to selectively inhibit their left finger's tapping while continuing their right finger's tapping and conversely. We assess (1) the development of the capacity to inhibit the stopping finger (number of supplementary taps after the stopping instruction) and (2) the development of the capacity to maintain the continuing finger (changes in the mean tempo and its variability for the continuing finger's tapping) and (3) the evolution of performance through trials. Results indicate that (1) TD children present an age-related increase in the capacity to inhibit and to maintain the left finger's tapping, (2) DCD exhibits persistent difficulties to inhibit the left finger's tapping, and (3) both groups improve their capacity to inhibit the left finger's movements through trials. In conclusion, the lateralized switching task provides a simple and fine tool to reveal differences in selective inhibition of symmetric movements in TD children and children with DCD. More theoretically, the specific improvement in selective inhibition of the left finger suggests a progressive development of inter-hemispheric communication during typical development that is absent or delayed in children with DCD.

Excessive motor overflow reveals abnormal inter-hemispheric connectivity in Friedreich ataxia

This study sought to characterise force variability and motor overflow in 12 individuals with Friedreich ataxia (FRDA) and 12 age- and gender-matched controls. Participants performed a finger-pressing task by exerting 30 and 70 % of their maximum finger force using the index finger of the right and left hand. Control of force production was measured as force variability, while any involuntary movements occurring on the finger of the other, passive hand, was measured as motor overflow. Significantly greater force variability in individuals with FRDA compared with controls is indicative of cortico-cerebellar disruption affecting motor control. Meanwhile, significantly greater motor overflow in this group provides the first evidence of possible abnormal inter-hemispheric activity that may be attributable to asymmetrical neuronal loss in the dentate nucleus. Overall, this study demonstrated a differential engagement in the underlying default processes of the motor system in FRDA.

Differences in cross modulation of physiological tremor in pianists and nonmusicians

PURPOSE

The study was undertaken to investigate the contralateral overflow effect on physiological tremors in pianists and nonmusicians. Group differences in cross modulation on underlying finger fractionated movement were characterized.

METHODS

Physiological tremors of the right index, middle, ring, and little fingers were recorded in 12 right-handed pianists and 12 matched nonmusician controls; meanwhile, two contralateral resistance protocols (unilateral handgrip using the left hand at slight and maximal efforts) were randomly conducted.

RESULTS

Digit tremors of the control and pianist groups were differentially modulated with the resistance protocols. An increase in gripping force led to cross excitations over 8-12 Hz digit tremors and interdigit tremor coupling for the nonmusicians. An opposite cross effect was noted for the pianists, who exhibited significant tremor suppression and the release of interdigit tremor coupling. Further analysis of tremor dynamics revealed that contralateral gripping reduced the complexity of digit tremors of the pianists but added to the tremor complexity of the nonmusicians.

CONCLUSIONS

Cross modulation on digit tremors suggests that pianists could centrally suppress unintended motor excitation across the midline. When the opposite hand is active, pianists have superior finger independence that allows them to achieve artistic aspects of musical performance.

Vision modulates corticospinal suppression in a functionally specific manner during movement of the opposite limb

The effect of vision on the excitability of corticospinal projections to the flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles of right human forearm was investigated before and during discrete movement of the opposite limb. An external force opposed the initial phase of the movement (wrist flexion) and assisted the reverse phase, so that recruitment of the wrist extensors was minimized. Three conditions were used as follows: viewing the inactive right limb (Vision), viewing the mirror image of the moving left limb (Mirror), and with vision of the right limb occluded (No Vision). Transcranial magnetic stimulation was delivered to the left motor cortex: before, at the onset of, or during the left limb movement to obtain motor evoked potentials (MEPs) in the muscles of the right forearm. At and following movement onset, MEPs obtained in the right FCR were smaller in the Vision condition than in the Mirror and No Vision conditions. A distinct pattern of variation was obtained for the ECR. In all conditions, MEPs in this muscle were elevated upon or following movement of the opposite limb. An additional analysis of ipsilateral silent periods indicated that interhemispheric inhibition plays a role in mediating these effects. Activity-dependent changes in corticospinal output to a resting limb during discrete actions of the opposite limb are thus directly contingent upon where one looks. Furthermore, the extent to which vision exerts an influence upon projections to specific muscles varies in accordance with the functional contribution of their homologs to the intended action.

Relative or absolute? Implications and consequences of the measures adopted to investigate motor overflow

Motor overflow is involuntary overt movement or covert muscle activity that cooccurs with voluntary movement. Overflow is present in several pathological conditions, as well as in neurologically healthy children and older adults, and can be induced in healthy young adults under effortful conditions. This motor phenomenon may provide insight into the underlying mechanisms and kinetic characteristics of voluntary and involuntary motor control in various populations. Although often measured behaviorally using force transduction techniques, different methods of calculating and presenting such overflow data have resulted in seemingly contradictory findings, with limited discussion of the advantages and limitations of different approaches. In this article, the authors examined the relevant literature to highlight significant methodological considerations for authors and readers conducting or appraising this type of research. Issues regarding the interpretation and reporting of findings are also discussed. Researchers are encouraged to continue using behavioral measures to create well-defined variables that enable the study of the kinematic characteristics of overflow, as these may offer promising new ways forward in better characterizing and understanding this intriguing movement phenomenon.

Overflow movements and white matter abnormalities in ADHD

Multiple motor abnormalities have been identified in some children with Attention Deficit/Hyperactivity Disorder (ADHD). These include persistence of overflow movements, impaired timing of motor responses and deficits in fine motor abilities. Motor overflow is defined as co-movement of body parts not specifically needed to efficiently complete a task. The presence of age-inappropriate overflow may reflect immaturity of the cortical systems involved in automatic motor inhibition. Theories on overflow movements consistently implicate impairments in white matter (WM) tracts, including the corpus callosum. WM connections might be altered selectively in brain networks and thus influence motor behaviours. We reviewed the scientific contributions on overflow movements and WM abnormalities in ADHD. They suggest that WM abnormalities in motor/premotor circuits, which are important for motor response inhibition, might be responsible for overflow movements in patients with ADHD.

Neurological soft signs in schizophrenia: investigating motor overflow

Investigation of neurological soft signs (NSSs) in schizophrenia may allow for a greater understanding of its underlying pathology. Motor overflow, involuntary movement occurring during voluntary movement, is a NSS thought to occur to a greater degree in schizophrenia. The aim of the current study was to replicate the only objective investigation which found enhanced motor overflow in schizophrenia and to further characterise its properties in a more systematic manner than previous research. The current study involved examining motor overflow production in 30 participants (15 with schizophrenia, 15 controls). Participants exerted 25 and 75% of their maximal force output, while overflow was monitored in the passive hand using linear variable differential transformer (LVDT) units. Patients with schizophrenia not only exhibited a significantly greater degree of motor overflow, compared to controls, they also exhibited a differential pattern of overflow production. Direct investigation of the cortical processes leading to motor overflow may provide a more complete understanding of the pathological relevance of motor overflow, and by extension NSSs, in schizophrenia.

Quantitative reference curves for associated movements in children and adolescents

Intensity of contralateral associated movements (AMs) is a measure of movement quality assessed using frequency and degree of AMs. A sample of 593 right-handed participants without disability (286 males, 307 females; aged 5y-18y 6mo) was studied with the Zurich Neuromotor Assessment (ZNA). The ZNA is a standardized testing procedure which assesses performance on standardized motor tasks according to timed performance and frequency and degree of AMs. In contrast to frequency and degree, intensity of AMs allowed the calculation of centiles which were quasi-continuous. Centile curves of contralateral AMs for the ZNA and data on inter- and intraobserver reliability are presented. The significance of age, sex, and side differences are discussed. Intensity of AMs offers clinical and scientific advantages for measurement of movement quality. There is a decrease of AMs with age depending on the complexity of tasks. Females showed consistently fewer AMs than males, whereas only minor side differences were shown.

The effects of age and attention on motor overflow production—A review

Motor overflow refers to overt involuntary movement, or covert muscle activity, that sometimes co-occurs with voluntary movement. Various clinical populations exhibit overflow. Motor overflow is also present in healthy children and the elderly, although in young adults, overt overflow is considered abnormal unless elicited under conditions of extreme force or muscle fatigue. Current theories of overflow imply that the corpus callosum may mediate production of this phenomenon. However, given that the corpus callosum is a conduit enabling the transfer of cortical information, surprisingly few studies have considered the cortical or subcortical structures underlying overflow. This review considers the developmental trend of motor overflow production, specifically in the upper-limbs, and the mechanisms thought to underlie this age-related phenomenon. Potential neurological correlates of motor overflow will be discussed in conjunction with higher order attentional processes which also regulate motor overflow production. Future research investigating the impact of attentional processes on overflow production may be particularly valuable for designing rehabilitation strategies for patients experiencing induced pathological overflow or conversely, to develop techniques to encourage the recovery of movement function in individuals with paretic limbs.

Developmental changes in unimanual and bimanual aiming movements

The aim of this study was twofold: (a) analyze the development of reaction time (RT) and movement time (MT) for bimanual and unimanual movements and (b) investigate the interaction of age and sex on the changes in RT and MT. Participants (5-, 8-, and 11-year-olds) were asked to aim at target buttons under three conditions of movement: unimanual, bimanual symmetrical, and bimanual nonsymmetrical. As expected, RTs for bimanual symmetrical movements were shorter than RTs for unimanual and bimanual nonsymmetrical movements in the 5-year-olds. By the age of 8, bimanual nonsymmetrical movements still yielded longer RTs than unimanual and bimanual symmetrical movements, which no longer differed from each other. Regarding MT, in the 2 younger groups there was an advantage of unimanual over bimanual symmetrical movements. The latter were executed faster than nonsymmetrical movements at all ages. These results suggest that the evolution of RT and MT with age reflects development of interhemispheric transfer of information. It appears that the functional improvement of such transfer, which depends on the corpus callosum, progressively enables contralateral motor inhibition and the coordination of complex bilateral movements. The exchange of movement feedback information could mature more slowly than that of feed-forward information, explaining the extended time course of MT evolution.

The influence of developmental coordination disorder and attention deficits on associated movements in children

The relationship between associated movements (AMs) and level of motor performance is not well understood. In this study we investigated whether children with developmental coordination disorder (DCD), with (n = 10) and without (n = 10) attention deficit hyperactivity disorder (ADHD), and a control group (n = 10), differed in the severity of AMs. A total AM severity score was obtained for each child by rating their performance on AM tasks. Both groups with motor difficulties had significantly more severe AMs than the control group. A significant correlation was found between level of motor performance and total AM scores (r = -.62). Our results suggest that level of motor performance should be considered in future research attempting to understand individual differences in severity of AMs as a function of motor, learning, and behavioural disorders.

The influence of attention and age on the occurrence of mirror movements

This study utilised a finger force task to investigate the influence of attention and age on the occurrence of motor overflow in the form of mirror movements in neurologically intact adults. Forty right-handed participants were recruited from three age groups: 20-30 years, 40-50 years, and 60-70 years. Participants were required to maintain a target force using both their index and middle fingers, representing 50% of their maximum strength capacity for that hand. Attention was directed to a hand by activating a bone conduction vibrator attached to the small finger of that hand. Based on Cabeza's (2002) model of hemispheric asymmetry reduction in older adults, it was hypothesised that mirror movements would increase with age. Furthermore, it was expected that when the attentional demands of the task were increased, motor overflow occurrence would be exacerbated for the older adult group. The results obtained provide support for the model, and qualified support for the hypothesis that increasing the attentional demands of a task results in greater motor overflow. It is proposed that the association between mirror movements and age observed in this study may result from an age-related increase in bihemispheric activation that occurs in older adults, who, unlike younger adults, benefit from bihemispheric processing for task performance.

Development of unimanual versus bimanual task performance in an isometric task

Sixty-three children between 5 and 12 years of age and 15 adults performed a unimanual and a bimanual isometric force task. The performance of the preferred hand in the unimanual task was compared to the performance of the preferred hand in the bimanual task. It was hypothesized that in the bimanual task the absolute error will be higher, there will be more irregularity and the participants will need more time due to the additional effort from the central nervous system, especially with respect to the communication between the hemispheres. Furthermore, in younger children bimanual force variability was expected to be higher due to developmental aspects concerning callosal maturation and attention. It was found that with respect to force generation the preferred hand was not affected by bilateral isometric force generation, but with respect to force regulation it was. The coefficient of variation (CV) of the force was 34% larger in the bimanual task as compared to the unimanual task. For the time to target force, the increase was 28%. With repetition of the trials the CV decreased in the bimanual task, but only in the youngest age group. During development there was no change in absolute error, yet there was a major reduction in force variability in the bimanual task. It is suggested that improvement in interhemispheric communication and in the ability to focus attention plays a role in the decrease in variability with age.

Investigating the cortical origins of motor overflow

Motor overflow refers to the involuntary movements which may accompany the production of voluntary movements. While overflow is not usually seen in the normal population, it does present in children and the elderly, as well as those suffering certain neurological dysfunctions. Advancements in methodology over the last decade have allowed for more convincing conclusions regarding the cortical origins of motor overflow. However, despite significant research, the exact mechanism underlying the production of motor overflow is still unclear. This review presents a more comprehensive conceptualization of the theories of motor overflow, which have often been only vaguely defined. Further, the major findings are explored in an attempt to differentiate the competing theories of motor overflow production. This exploration is done in the context of a range of neurological and psychiatric disorders, in order to elucidate the possible underlying mechanisms of overflow.

Callosal contribution to procedural learning in children

A previous study in acallosal patients (De Guise, et al., 1999) has demonstrated the crucial role of the corpus callosum (CC) in a procedural learning task that requires the participation of both hemispheres. Because children often display limitations in interhemispheric communication linked to callosal immaturity, we expected that they would have difficulties learning a procedural skill that involved interhemispheric integration during its acquisition, but not when the skill was learned intrahemispherically. To test this hypothesis, 40 children, divided into 4 age groups (6 to 8 years, 9 to 11 years, 12 to 14 years, and 15 to 16 years), performed a modified version of the serial reaction time task developed by Nissen and Bullemer (1987). This task involves uni- or bimanual key-pressing responses to a fixed sequence of 10 visual stimuli that are repeated 80 times. All the children were able to learn the visuomotor skill in the unimanual condition and to transfer it interhemispherically. However, only the older children (12 years and over) learned the task in the bimanual (interhemispheric) condition. The results indicate that the maturation of the CC affects interhemispheric acquisition of a procedural skill in two different ways: While the immature CC appears to be sufficient to transfer a skill acquired by one hemisphere, a mature CC seems to be required to learn the skill bihemispherically. The latter skill was achieved around the age of 12, coinciding with the end of the maturation cycle of the CC. Although the young children were unable to learn the bimanual task implicitly, some of them showed explicit knowledge of the procedure, confirming once again the dissociation between explicit and implicit memory suggested by Squire (1992).

Do associated reactions in the upper limb after stroke contribute to contracture formation?

OBJECTIVE

To establish (1) whether associated reactions could contribute to contracture formation and (2) whether the presence of spasticity was essential for their expression, after stroke.

SUBJECTS

Subjects were 24 hemiparetics within 13 months of a stroke, unselected for contracture or spasticity.

MAIN OUTCOME MEASURES

Associated reactions were identified by the presence of muscle activity in the affected biceps brachii and quantified as the amount of affected elbow flexor torque produced during a moderate contraction of either the contralateral biceps brachii or the contralateral quadriceps muscles. Contracture was measured as loss of elbow joint range of motion and spasticity as the presence of abnormal reflex activity.

RESULTS

Associated reactions were present in at least one testing condition in seven subjects. During contractions of the contralateral biceps brachii, the median amount of elbow flexor torque produced was 0.39 (interquartile range, IQR 2.5) Nm while during contractions of the contralateral quadriceps muscle it was 0.19 (IQR 1.6) Nm. Associated reactions were not associated with contracture (p = 0.39) which was present in over half of the subjects. The incidence of associated reactions was about the same as that of spasticity, but the two were not related (p = 0.61).

CONCLUSIONS

Even though associated reactions were present in 29% of the subjects during moderate contraction of the contralateral muscles, they were not large, nor were they associated with contracture or spasticity, suggesting that this phenomenon is not usually a major problem for everyday function after stroke.

Muscle activation in the contralateral passive shoulder during isometric shoulder abduction in patients with unilateral shoulder pain

Studies have shown an increased muscle activation at the opposite passive side during unilateral contractions. The purpose of the present study was to examine the influence of pain on muscle activation in the passive shoulder during unilateral shoulder abduction. Ten patients with unilateral rotator tendinosis of the shoulder and nine healthy controls performed unilateral maximal voluntary contractions (MVC) and sustained submaximal contractions with and without subacromial injections of local anaesthetics of the afflicted shoulder. Muscle activation was recorded by electromyography (EMG) from the trapezius, deltoid, infraspinatus and supraspinatus muscles in both shoulders. During MVCs, the EMG amplitude from muscles of the passive afflicted side was not different in patients and controls, and was not influenced by pain alterations. In contrast, the EMG amplitude from the muscles of the passive unafflicted side was lower in the patients and increased after pain reduction. During the sustained submaximal contraction the EMG amplitude increased gradually in the passive shoulder to 15-30% of the EMG amplitude observed during MVC. This response was not influenced by differences in pain. We conclude that muscle activation of the passive shoulder was closely related to the activation of the contracting muscles and thus related to central motor drive, and not directly influenced by changes in pain.

The Specificity of Motor Skill and Manual Asymmetry: A Review of the Evidence and Its Implications

Results of investigations on gaining control of limb movements are reviewed, and their contribution to understanding the development of manual asymmetries is discussed in relation to the discrimination and programming of appropriate neuromuscular resources. An examination of the relevant evidence on number and types of manual asymmetries recorded provides strong grounds for concluding that where asymmetries occur, they simply represent a further example of the well-documented activity-specific nature of motor skills and of the extremely lengthy periods of learning or experience needed for their acquisition and perfection. This specificity of motor skill and manual asymmetry also readily accounts for most of the discrepancy usually reported between assessments of hand preference and performance differences between hands, because these alternative measures of handedness have rarely employed the same range or variety of tasks.

Handedness and performance variability as factors influencing mirror movement occurrence

A finger flexion task was used to investigate the effect of hand preference and performance variability on intensity of mirror movement. Right- and left-handed subjects were asked to maintain target forces, with either their index or small finger, that represented 25, 50, or 75% of their maximum strength capacity for the active finger. Greater mirror movement occurred when the small finger was active, and where there was greater variability in task performance, while mirror movement intensity was less when the dominant hand and the index finger were active. These findings were consistent with the cortical activation explanation of motor overflow (Todor & Lazarus, 1986a), and suggest that task variability is an important factor influencing motor overflow production. It was concluded that, if performance variability reflects the efficiency of cortical activation underlying control of a voluntary task, then refined cortical control decreases the potential for motor overflow to occur. However, it is necessary to clarify the relationship between hand preference, performance variability, and motor overflow, perhaps by examining the neural pathways involved in motor overflow production.

Hemispheric asymmetry of transcallosal inhibition in man

The transcallosal connecting fibres linking corresponding projection areas of the same muscles of the right and left primary motor cortex may play an important role in control of unilateral movements. It appears that they have mainly inhibitory effects. This was further evaluated by transcranial magnetic stimulation using two focal coils placed on the optimal positions, i.e. the positions with the lowest thresholds at the motor representation areas of the first dorsal interosseous muscle of the left and right sides. A conditioning stimulus was given to one hemisphere 10 ms prior to the test stimulus at the opposite hemisphere. The inhibition was evaluated as relative amplitude reduction. Eleven normal right-handed subjects and 11 normal left-handed subjects participated in this study. Handedness was evaluated by the Oldfield inventory. It was found that in right-handers the inhibition after stimulation of the "dominant" left hemisphere was more marked than after stimulation of the "non-dominant" right hemisphere. In contrast, the group of left-handed subjects showed inhomogeneous findings with either right- or left-side predominant inhibition. It is concluded that not handedness but hemispheric dominance contributes to the laterality of inhibition. The results point to a superior role of the language-dominant hemisphere in governing inter-hemispheric control of motor cortical connections, supporting the view that the "language-dominant" hemisphere is also "motor dominant".

Mirror movements in normal adult subjects

Intensity of mirror movements occurring under specific task conditions in normal adults was investigated using a finger flexion task. Subjects were asked to sustain target pressures using different fingers. Greater pressures of mirror movement were recorded when the weaker, small finger of either hand performed the task. The target pressure which subjects were asked to sustain did not influence the amount of mirror movement exhibited by either males or females, even though higher target forces required a significantly greater percentage of total finger strength. On average, males exhibited the same quantity of mirror movements as female subjects, despite the force requirements of the task representing for them a significantly smaller percentage of total finger strength. Moreover, when the right hand performed the experimental tasks, less mirror movement was exhibited than when the left hand was active. Thus, the left hand showed stronger mirror movements. The findings were consistent with previous research using children as subjects, although the nonsignificant effects of gender and pressure were unexpected and need to be examined further. It appears that, while the force requirement of the task does influence the magnitude of mirror movement, it is not the principle determinant.

Co-activation of ipsi- and contralateral muscle groups during contraction of ankle dorsiflexors

Seventeen adult, healthy subjects, age 38.4 +/- 0.24 years (mean +/- SEM) 7 of which were females, were studied. Each subject was seated on a specially designed chair with trunk and legs fixed and the foot strapped to a rigid plate that was attached to a load cell. The position of the strap was adjusted so as to lie across the foot at the level of the metatarsal bones. The knee and ankle joints were adjusted to 90 degrees. To record EMG activity, pairs of surface electrodes were placed over the belly of both the right and left tibialis anterior, quadriceps, hamstring and contralateral triceps surae muscles. Two experimental paradigms were used, A and B. In A the subject was asked to sustain maximum voluntary contraction (MVC) of the ankle dorsiflexors until the force decreased to 50% of the initial value; in B the subject was asked to carry out contractions of the ankle dorsiflexors for 6 seconds followed by 4 sec relaxation periods. The initial contraction was 20% of MVC followed by 40, 60, 80 and 100% of MVC which represented one cycle. The subject was asked to repeat this cycle 10 times. Voluntary contraction of ankle dorsiflexors was regularly accompanied by activation of other muscles, usually first in the same leg, later in the contralateral leg during MVC of ankle dorsiflexors. When intermittent contractions with step wise increments of force developed by the ankle dorsiflexors were carried out, co-activation of ipsilateral and contralateral muscle groups occurred before the force of the contracting muscles decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of attention in the regulation of associated movement in children

The effect of attentional processes in regulating associated movement was studied in 10 male children in each of five age-groups from six to 16 years. They were asked to squeeze their index finger and thumb to 75 per cent of their own maximal volitional force under three conditions: a spontaneous baseline condition, a sensory feedback condition and a post-training condition without sensory feedback. Children of all ages were able to reduce the magnitude of associated movements during the sensory feedback condition. In the post-training condition some of the ability to inhibit was lost, particularly for the six-year-olds. This supports the view that the integration of higher order processes, such as attention, with lower-level neuromotor inhibitory mechanism, plays a role in the reduction of associated movement with increasing age. Implications for therapy with clinical populations are discussed.

Practice and Assimilation Effects in a Multilimb Aiming Task

When two limbs are required to move different distances simultaneously, assimilation effects are shown: The shorter distance limb tends to overshoot the target, whereas the longer distance limb undershoots. The effect of practice on assimilation effects was studied in two experiments, using a simultaneous four-limb aiming task. When subjects were required to move their left limbs a shorter distance than the right (5 cm vs. 9 cm), the right limbs moved a lesser distance and had greater variable and overall errors relative to a group required to move all limbs the same distance (9 cm). Practice reduced assimilation effects in the lower limbs, but spatial assimilations were present throughout 125 acquisition trials with KR and 50 no-KR transfer trials, spanning 24 hours. When the upper limbs were required to move a greater distance than the lower limbs (15 cm vs. 9 cm), the lower limbs showed longer distances and increased overall errors early in practice compared to the lower limbs of a group required to move all limbs 9 cm. With practice, the between-group differences decreased, with no assimilation effects shown on the transfer trials. The results suggest that neural crosstalk is greater between left and right sides than between upper and lower limbs. Results are discussed in light of the functional cerebral space model of simultaneous actions.

Age differences in the magnitude of associated movement

Using a quantitative measure of unintended mirror-movements in the contralateral limb during a unimanual task, the magnitude of associated movement across the ages from six to 16 years was determined. Male children in five age-groups (means 6.5, 8.5, 10.4, 12.4 and 16.5 years) were asked to squeeze their index finger and thumb together to various percentages of their own maximal volitional force. Results indicate that the 6.5-year-old group differ from all other age-groups, exhibiting significantly greater associated movements at all levels of force. The results are discussed in terms of the development of inhibitory control over innate neuromotor synergies.

A modified finger lift test reveals an asymmetry of motor overflow in adults

A method of eliciting motor overflow in neurologically intact adults is reported. A weight was placed on either the middle or ring finger of the left or right hand, and the subject was instructed to lift that finger. Involuntary finger lifts of the contralateral hand were recorded. There were 32 right-handers per experiment. In Experiments I and II, the amount of weight placed on the subject's finger was in proportion to body weight, whereas in Experiment III, it was in proportion to each finger's strength. Across experiments, motor overflow was more prevalent when the left, rather than the right, hand was weighted. This shows that the asymmetry in motor overflow previously reported in children and brain-damaged adults also occurs in healthy adults, and that this movement asymmetry is not an artifact of the relative weakness of the left hand in right-handed individuals.

Bimanual Stereotypes

Five-, 7-, and 9-year-old children were trained and tested in a bimanual coordination task that required them to rotate two cranks (either at the same or at different velocities) using mirror (inwards or outwards) or parallel movements (clockwise or counterclockwise). The task consisted of tracing two lines of different slants, by turning the two cranks either at the same velocity (to draw the 45 degrees slanted line) or at different velocities (to draw the 22 degrees line). The same-velocity condition resulted in significantly better performance than the different-velocities condition with the age x angle interaction: the performance in the different-velocities condition improved considerably at 9 years of age. Mirror movement induced faster and more accurate performance relative to parallel movements in the same-velocity condition but not in the different-velocities condition. This difference was much greater in 5- and 7-year-olds than in 9-year-olds. The results are interpreted as reflecting a decreasing influence of motor constraints on bimanual coordination.

Exertion level and the intensity of associated movements

Associated movements in the contralateral limbs were measured quantitatively for 42 seven- to eight-year-old children who wrote with the right hand. Associated movements of the contralateral homologous muscles systematically increased as a function of the intensity of contraction of the active hand. The associated movements were more intense when the left hand was active. The order of hand use markedly affected the lateral asymmetry, indicating that the right and left hands were affected differentially by previous activity. Associated movements of the contralateral antagonist muscles were also observed, and their frequency varied as a function of active hand and exertion level.

Neuromotor maturation and psychological performance: a developmental study

Groups of 50 normal kindergarten and 50 first-grade children were examined three times at six-month intervals on the extended neuromotor examination for children, as well as on measures of reading achievement and language performance. The joint effect of five neuromotor measures accounted for a substantial percentage of variance in reading achievement and language performance 12 months later. As a global measure, neuromotor status therefore may constitute a reliable, independent criterion of developmental age for psychological investigations of young, normal children. The best individual predictors of psychological outcome were mirror movements and speed of timed motor repetitions, while reading achievement and automated naming speed were the dependent measures most closely associated over time with neuromotor status. Such findings suggest that the individual motor signs may also provide indirect clues about the presumed functional relationship between development of motor co-ordination and language competence.

Movement-related potentials during development: a replication and extension of relationships to age, motor control, mental status and IQ

Three age groups of normals (children, preadolescents, and adults) and a group of mentally retarded adults performed a noncued button press task from which averaged movement-related potentials (MRPs) were derived. MRP wave shapes replicated our previously reported modal waveform types, except for the preadolescents, who showed no modal MRP. The normal groups showed a developmental shift in the prevalence of waveforms with the retarded differing from normal adults. The modal child waveform had a large amplitude positive-negative-positive form; the retarded had a uniphasic positive form; while normal adults showed the usual negative form. Major MRP types among children could not be attributed to differences in sampling or number of the trials averaged, or to trial-to-trial MRP variability. Background EEG activity did not differ in different modal MRP types. Modal child MRPs showed an initial peak positivity at Fz, and a late peak at Cz. The retarded had a sustaining central positivity developed by midepoch. MRP positivity and negativity were related to age, inhibition of extraneous eye movement (EM), and IQ. In children, greater cognitive proficiency is associated with adult-like MRP. The results suggest that positivity, in part, reflects a subject's efforts at inhibiting movement extraneous to the instructed task.

Associated movements as a measure of developmental age

Fifty normal kindergarten and 50 first-grade children were examined three times at six-month intervals for synkineses to stress gaits and mirror movements to finger lifting, finger spreading, and timed motor maneuvers. Motor signs in the age-sensitive range showed substantial individual differences between children of the same chronological age. The frequency of associated movements changed reliably in the expected direction over a 12-month period, and within each domain of neuromotor function the individual motor signs conformed to a stable sequence of developmental stages. It is concluded that age-appropriate motor signs for associated movements are a reliable measure of developmental age, in contrast to chronological age, among elementary-school children.