Motor overflow and attentional processes in normal school-age children

Biological and environmental factors may affect children's executive function through motor and sensorimotor development: Preterm birth and cerebral palsy

Disruptive biological and environmental factors may undermine the development of children's motor and sensorimotor skills. Since the development of cognitive skills, including executive function, is grounded in early motor and sensorimotor experiences, early delays or impairments in motor and sensorimotor processing often trigger dynamic developmental cascades that lead to suboptimal executive function outcomes. The purpose of this perspective paper is to link early differences in motor/sensorimotor processing to the development of executive function in children born preterm or with cerebral palsy. Uncovering such links in clinical populations would improve our understanding of developmental pathways and key motor and sensorimotor skills that are antecedent and foundational for the development of executive function. This knowledge will allow the refinement of early interventions targeting motor and sensorimotor skills with the goal of proactively improving executive function outcomes in at-risk populations.

Sex Effects on Mirror Overflow during Finger Tapping in Children with ADHD

OBJECTIVES

The presence of excessive mirror overflow in children with Attention Deficit/Hyperactivity Disorder (ADHD) is discussed in numerous published reports. These reports, however, include a limited age range in their samples. The objective of this study is to examine the effects of diagnosis and sex on mirror overflow and standard deviation (SD) of tap time in children with and without ADHD across a larger age range (5-12 years) of children.

METHODS

One-hundred and forty-eight children with ADHD and 112 age- and sex-matched typically developing (TD) children completed a finger sequencing task. Mirror overflow, SD of tap time, and mean tap time were measured using finger twitch transducers.

RESULTS

Results reveal a significant diagnostic effect on mirror overflow such that boys and girls with ADHD demonstrate increased overflow compared to same-sex TD children. Boys with ADHD demonstrated more variable tap times compared to TD boys; no diagnostic effect was observed in the girls.

CONCLUSIONS

Boys with ADHD exhibit anomalous motor variability; girls with ADHD show similar levels of variability as TD girls. Boys and girls with ADHD exhibit similar levels of excessive mirror overflow. This lack of sex differences on mirror overflow is distinct from reports finding sex effects on overflow and could result from an examination of a broader age range than is included in prior reports. Adolescent data would provide a greater understanding of the trajectory of anomalous mirror overflow across development. Examination of functional and structural connectivity would expand the current understanding of the neurobiological foundation of motor overflow.

From Hemispheric Asymmetry through Sensorimotor Experiences to Cognitive Outcomes in Children with Cerebral Palsy

Recent neuroimaging studies allowed us to explore abnormal brain structures and interhemispheric connectivity in children with cerebral palsy (CP). Behavioral researchers have long reported that children with CP exhibit suboptimal performance in different cognitive domains (e.g., receptive and expressive language skills, reading, mental imagery, spatial processing, subitizing, math, and executive functions). However, there has been very limited cross-domain research involving these two areas of scientific inquiry. To stimulate such research, this perspective paper proposes some possible neurological mechanisms involved in the cognitive delays and impairments in children with CP. Additionally, the paper examines the ways motor and sensorimotor experience during the development of these neural substrates could enable more optimal development for children with CP. Understanding these developmental mechanisms could guide more effective interventions to promote the development of both sensorimotor and cognitive skills in children with CP.

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.

Contralateral Associated Movements Correlate with Poorer Inhibitory Control, Attention and Visual Perception in Preschool Children

Contralateral associated movements (CAMs) frequently occur in complex motor tasks. We investigated whether and to what extent CAMs are associated with inhibitory control among preschool children in the Swiss Preschoolers' Health Study. Participants were 476 healthy, typically developing children (mean age = 3.88 years; 251 boys) evaluated on two consecutive afternoons. The children performed the Zurich Neuromotor Assessment, the statue subtest of the Neuropsychological Assessment for Children (NEPSY), and cognitive tests of the Intelligence and Development Scales-Preschool (IDS-P). CAMs were associated with poor inhibitory control on the statue test and poor selective attention and visual perception on the IDS-P. We attributed these findings to preschoolers' general immaturity of the central nervous system.

Neurological soft signs are associated with attentional dysfunction in children with attention deficit hyperactivity disorder

INTRODUCTION

Inattention is one of the core symptoms of Attention Deficit Hyperactivity Disorder (ADHD). Most of patients with ADHD show motor impairment, consisting in the persistence of neurological soft signs (NSS). Our aim was to evaluate attentional and motor functioning in an ADHD sample and healthy children (HC) and possible link between attentional dysfunction and motor impairment in ADHD.

METHOD

Twenty-seven drug-naive patients with ADHD and 23 HC were tested with a test battery, measuring different aspects of attention. Motor evaluation has provided three primary variables: overflow movements (OM), dysrhythmia and total speed of timed activities.

RESULTS

Compared to HC, patients were impaired in a considerable number of attentional processes and showed a greater number of NSS. Significant correlations between disturbances of attention and motor abnormalities were observed in ADHD group.

CONCLUSION

Our findings suggest that attentional processes could be involved in the pathophysiology of the NSS and add scientific evidence to the predictive value of NSS as indicators of the severity of functional impairment in ADHD. Given the marked improvement or complete resolution of NSS following treatment with methylphenidate, we suggest that evaluation of NSS is useful to monitor the effectiveness of pharmacological treatment with MPH in ADHD.

Specialization of the motor system in infancy: from broad tuning to selectively specialized purposeful actions

In executing purposeful actions, adults select sufficient and necessary limbs. But infants often move goal-irrelevant limbs, suggesting a developmental process of motor specialization. Two experiments with 9- and 12-month-olds revealed gradual decreases in extraneous movements in non-acting limbs during unimanual actions. In Experiment 1, 9-month-olds produced more extraneous movements in the non-acting hand/arm and feet/legs than 12-month-olds. In Experiment 2, analysis of the spatiotemporal dynamics of infants' movements revealed developmental declines in the spatiotemporal coupling of movements between acting and non-acting arms. We also showed that the degree of specialization in infants' unimanual actions is associated with individual differences in motor experience and visual attention, indicating the experience-dependent and broad functional nature of these developmental changes. Our study provides important new insights into motor development: as in cognitive domains, motor behaviours are initially broadly tuned to their goal, becoming progressively specialized during the first year of life.

Mindful movement and skilled attention

Bodily movement has long been employed as a foundation for cultivating mental skills such as attention, self-control or mindfulness, with recent studies documenting the positive impacts of mindful movement training, such as yoga and tai chi. A parallel “mind-body connection” has also been observed in many developmental disorders. We elaborate a spectrum of mindfulness by considering ADHD, in which deficient motor control correlates with impaired (disinhibited) behavioral control contributing to defining features of excessive distractibility and impulsivity. These data provide evidence for an important axis of variation for wellbeing, in which skillful cognitive control covaries with a capacity for skillful movement. We review empirical and theoretical literature on attention, cognitive control, mind wandering, mindfulness and skill learning, endorsing a model of skilled attention in which motor plans, attention, and executive goals are seen as mutually co-defining aspects of skilled behavior that are linked by reciprocal inhibitory and excitatory connections. Thus, any movement training should engage “higher-order” inhibition and selection and develop a repertoire of rehearsed procedures that coordinate goals, attention and motor plans. However, we propose that mindful movement practice may improve the functional quality of rehearsed procedures, cultivating a transferrable skill of attention. We adopt Langer’s spectrum of mindful learning that spans from “mindlessness” to engagement with the details of the present task and contrast this with the mental attitudes cultivated in standard mindfulness meditation. We particularly follow Feldenkrais’ suggestion that mindful learning of skills for organizing the body in movement might transfer to other forms of mental activity. The results of mindful movement training should be observed in multiple complementary measures, and may have tremendous potential benefit for individuals with ADHD and other populations.

Concurrent motor and cognitive function in multiple sclerosis: a motor overflow and motor stability study

OBJECTIVE AND BACKGROUND

The interplay between motor and cognitive functions during performance of concurrent tasks is not fully understood but is known to vary depending on task characteristics and across clinical populations. Our controlled study examined how a concurrent digit span task affected a motor stability and motor overflow task in patients with multiple sclerosis (MS).

METHOD

We asked 22 patients with MS and 22 matched controls to exert force on a transducer using 1 index finger at a time. We measured their motor stability (accuracy of voluntary force production) and motor overflow (involuntary force produced by the opposite, inactive finger). During half of the trials, the participants concurrently performed a digit span task.

RESULTS

Overall, the patients with MS had more motor overflow and less motor stability than the controls; these measures correlated with the patients' disease severity. Adding the concurrent task affected motor stability; this relationship varied with the required level of exerted force. Motor overflow was lower during trials with the concurrent task. The concurrent task affected patients and controls similarly for both motor stability and overflow.

CONCLUSIONS

This study demonstrates preserved motor function in a concurrent-task paradigm in patients with MS, and sheds further light on the relationship between attention and motor function in both the patients and controls. This research may help to inform rehabilitation for everyday life situations in which patients routinely perform cognitive and motor tasks simultaneously.

On the other hand: overflow movements of infants' hands and legs during unimanual object exploration

Motor overflow is extraneous movement in a limb not involved in a motor action. Typically, overflow is observed in people with neurological impairments and in healthy children and adults during strenuous and attention-demanding tasks. In the current study, we found that young infants produce vast amounts of motor overflow, corroborating claims of symmetry being the default state of the motor system. While manipulating an object with one hand, all 27 of the typically developing 4.5- to 7.5-month-old infants who we observed displayed overflow movements of the free hand (on 4/5 of unimanual actions). Mirror-image movements of the hands occurred on 1/8 of unimanual actions, and the hands and legs moved in synchrony on 1/3 of unimanual acts. Motor overflow was less frequent when infants were in a sitting posture and when infants watched their acting hand, suggesting that upright posture and visual examination may help to alleviate overflow and break obligatory symmetry in healthy infants.

ADHD: volumetry, motor, and oculomotor functions

The use of quantitative neuroimaging (volumetry), motor, and oculomotor assessments for studying children with attention-deficit/hyperactivity disorder (ADHD) has grown dramatically in the past 20 years. Most evidence to date suggests that anomalous basal ganglia development plays an important role in early manifestation of ADHD; however, widespread cerebellar and cortical delays are also observed and are associated with the behavioral (cognitive, motor, oculomotor) phenotype in children with ADHD. These motor and "executive" control systems appear to develop in parallel, such that both systems display a similar protracted developmental trajectory, with periods of rapid growth in elementary years and continued maturation into young adulthood. Development of each system is dependent on the functional integrity and maturation of related brain regions, suggesting a shared neural circuitry that includes frontostriatal systems and the cerebellum (i.e., those identified as anomalous in studies of volumetry in ADHD). Motor and oculomotor paradigms provide unique opportunities to examine executive control processes that exist at the interface between movement and cognition in children with ADHD, also linking cognition and neurological development. The observed pattern of volumetric differences, together with the known parallel development of motor and executive control systems, appears to predict motor and oculomotor anomalies in ADHD, which are highly relevant, yet commonly overlooked in clinical settings.

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.

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.

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.

Overflow movements predict impaired response inhibition in children with ADHD

Neurologic models proposed to explain mechanisms underlying ADHD have emphasized deficits in response inhibition. Age-inappropriate overflow movements, e.g., mirror movements, are motor signs thought to reflect immaturity in cortical systems involved in automatically (unconsciously, without explicit effort) inhibiting extraneous movement. We investigated the hypothesis that the presence of excessive overflow movements would predict measures of conscious, effortful response inhibition (conflicting and contralateral motor response tests) in children with ADHD. 42 children with ADHD and 30 controls, ages 8 through 12 years, participated. Children with ADHD showed significantly more overflow movements than did controls and made more errors on the conflicting and contralateral motor response tests. Multiple linear regression analysis indicated that overflow movements predicted performance on measures of motor response inhibition. For one of those measures, the contralateral motor response test, there was a significant interaction with diagnosis, such that overflow predicted response inhibition in ADHD but not in controls. The findings suggest that overflow movements, which can be readily observed as part of clinical examination, are more evident in children with ADHD. Positive correlations between measures of overflow movements and measures of response inhibition suggest that closely associated neural mechanisms underlie these deficits and support hypotheses that age-inappropriate overflow reflects immaturity of cortical systems involved in automatic inhibition.

Cortical correlates of neuromotor development in healthy children

OBJECTIVE

To examine the relationship between acquisition of fine motor skills in childhood and development of the motor cortex.

METHODS

We measured finger tapping speed and mirror movements in 43 healthy right-handed subjects (6-26 years of age). While recording surface electromyographic activity from right and left first dorsal interosseus, we delivered focal transcranial magnetic stimulation (TMS) over the hand areas of each motor cortex. We measured motor evoked potential (MEP) threshold, and ipsilateral (iSP) and contralateral (CSP) silent periods.

RESULTS

As children got older, finger speeds got faster, MEP threshold decreased, iSP duration increased and latency decreased. Finger tapping speed got faster as motor thresholds and iSP latency decreased, but was unrelated to CSP duration. In all subjects right hemisphere MEP thresholds were higher than those on the left and duration of right hemisphere CSP was longer than that on the left. Children under 10 years of age had higher left hand mirror movement scores, and fewer left hemisphere iSPs which were of longer duration.

CONCLUSIONS

Maturation of finger tapping skills is closely related to developmental changes in the motor threshold and iSP latency. Studies are warranted to explore the relationship between these measures and other neuromotor skills in children with motor disorders.

SIGNIFICANCE

TMS can provide important insights into certain functional aspects of neurodevelopment in children.

Quantitative EMG analysis to investigate synergistic coactivation of ankle and knee muscles during isokinetic ankle movement. Part 1: time amplitude analysis

Synergy generally refers to the coordinated action of several motor elements to produce a specific motor task, either intentionally or automatically. One example is motor irradiation, a sudden spread of synergistic muscular coactivation resulting from a forceful single joint movement. To investigate this type of synergy pattern, a quantitative EMG approach was employed to characterize explicit neuromuscular synergy in the ankle-knee complex during maximal ankle isokinetic contraction. In the present study, isokinetic ankle contractions, both dorsiflexion and plantarflexion, at four different speeds (30, 60, 120, and 240 degrees/s) were studied in a normal adult population (N=11) to assess synergistic coactivation of the prime movers (tibialis anterior and gastrocnemius) and irradiated muscles (ipsilateral and contralateral rectus femoris and biceps femoris) of the ankle-knee complex. Electromyographic signals were collected with surface EMG electrodes and processed with traditional time-amplitude analysis to examine specific neural control strategies. The data generally supported several empirical assumptions common to neurological facilitation techniques. (1) Motor irradiation to the knee muscles due to ankle muscle isokinetic contraction was strongly directionally dependent. (2) Motor irradiation to the ipsilateral knee muscles due to ankle isokinetic contraction was speed dependent. (3) The prime movers demonstrated a similar control strategy, irrespective of different contraction speeds.

Brain mapping of bilateral interactions in attention deficit hyperactivity disorder and control boys

OBJECTIVES

Children with attention deficit hyperactivity disorder (ADHD) are thought to have deficits in attentional control, whereas the status of deficits at visual and pre-motor processing stages is unclear.

METHODS

The timing of such deficits was examined with event-related potential (ERP) microstates (stimulus- and response-related) and continuous force recordings in 15 ADHD and 16 control boys in a choice reaction time task. Unilateral and bilateral stimulus and response conditions were used to assess bilateral interactions at visual, central, and pre-motor stages.

RESULTS

ADHD boys showed poorer performance, particularly in the bilateral conditions. In the visual P1 microstates, they exhibited less suppression of visual evoked potential (VEP) amplitudes but similar speeding of VEP latencies in the bilateral compared to the summed unilateral condition. The central P3 and pre-/post-response microstates were attenuated and topographically altered in ADHD boys. The attenuation was most pronounced in the bilateral condition and was similar for stimulus- and response-related averages. The lateralized readiness potential was also reduced in ADHD boys; this was most pronounced for the left hand responses.

CONCLUSIONS

Brain mapping during uni- and bilateral stimulus and response conditions thus indicates multilevel deficits in ADHD boys affecting visuo-attentional, central, and pre-motor processes.

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.

Predictive value of placebo methylphenidate

The effects of methylphenidate in 20 children with attention-deficit disorder between the ages of 7 and 12 years were assessed in a double-blind, placebo/drug counterbalanced study. Measures of outcome included the Teacher Rating Scale and Abbreviated Parent Rating Scale: digits, words, and visual sequencing; motor control; and a maze test. The Teacher Rating Scale placebo-drug difference correlated more significantly with the outcome measures than the baseline-drug difference. The study underlines the validity of a multimeasure placebo/drug trial in evaluating the efficacy of methylphenidate in children with attention-deficit disorder.

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.