Developmental Trajectory of Motor Deficits in Preschool Children with ADHD

Motor deficits persisting into childhood (>7 years) are associated with increased executive and cognitive dysfunction, likely due to parallel neural circuitry. This study assessed the longitudinal trajectory of motor deficits in preschool children with ADHD, compared to typically developing (TD) children, in order to identify individuals at risk for anomalous neurological development. Participants included 47 children (21 ADHD, 26 TD) ages 4-7 years who participated in three visits (V1, V2, V3), each one year apart (V1=48-71 months, V2=60-83 months, V3=72-95 months). Motor variables assessed included speed (finger tapping and sequencing), total overflow, and axial movements from the Revised Physical and Neurological Examination for Subtle Signs (PANESS). Effects for group, visit, and group-by-visit interaction were examined. There were significant effects for group (favoring TD) for finger tapping speed and total axial movements, visit (performance improving with age for all 4 variables), and a significant group-by-visit interaction for finger tapping speed. Motor speed (repetitive finger tapping) and quality of axial movements are sensitive markers of anomalous motor development associated with ADHD in children as young as 4 years. Conversely, motor overflow and finger sequencing speed may be less sensitive in preschool, due to ongoing wide variations in attainment of these milestones.     

Maturation of lower extremity EMG responses to postural perturbations: relationship of response-latencies to development of fastest central and peripheral efferents

Summary EMG responses to toe-up tilt perturbations on a movable platform system were analysed in 86 children between the age of 12 months and 13 years. To assess the relative contribution of peripheral and central nerve conduction properties, a concomitant recording of the fastest efferent pathways in the central and peripheral motor system was made using non-invasive transcranial magnetic stimulation of motor cortex and peripheral nerve roots. This allowed the determination of the fastest downstream efferent connection times from motor cortex to lumbar motor neuron pools and to measure the fastest efferent conduction from these motor neuron pools to effector muscles in the lower leg. The sequence observed for stance stabilizing EMG responses was similar to that obtained in earlier studies with short latency (SL) and middle latency (ML) components occurring in the stretched triceps surae muscle and long latency (LL) responses occurring in the non-stretched tibialis anterior muscle. Homologous responses were also obtained in upper leg muscles, being recruited consistently later than those in lower leg muscles across all age groups. In the short latency range two different SL1- and SL2-responses were obtained in children of all age groups as well as in adult controls. Both the SL1- and the SL2-responses showed a flat developmental profile, reaching adult values between 20 and 30 months of age which correlated with that of the fastest efferents from lumbar motor neuron pools to leg muscles, i.e. the final motor path. ML-responses showed a steeper developmental profile. The LL-responses in TA muscle showed an even more prolonged maturational profile which fitted well with the development of central conduction times between motor cortex and the spinal motor neuron pools. The sum of the fastest possible afferent conduction times as estimated from somatosensory evoked potentials, and the fastest downstream efferent conduction times from motor cortex to effector muscles was smaller than the onset latencies of LL-responses. The resulting transcerebral processing time exceeded the sum of the fastest up- and downstream conduction times by up to 70 ms. This suggests a prolonged transcerebral processing loop for the proprioceptive input to LL-responses rather than a transcortical loop.     

Persistent mirror movements: force and timing of “mirroring” are task-dependent

A simple isometric motor task was used to quantify intended and unintended finger movements in two subjects (father and son) with persistent mirror movements. One hand voluntarily changed grip force between thumb and index finger at different amplitudes and frequencies, while the other hand was to maintain a constant force. During all experimental conditions the steady hand showed insuppressible, highly cross-correlated contractions, compatible with bilateral distribution of a single motor command to the spinal cord. However, these associated movements were not strictly mirror images, nor did they show a fixed relationship to the voluntary movements across experimental conditions. The ratio of mirror to voluntary movement ranged from 1.4 to 19.1% and from 3.4 to 78.4% in the two subjects and was directly related to voluntary strength and speed. At maximum speed, mirror activity tended to precede voluntary activity, while it was delayed in slow force changes. Comparable time lags were not found in control subjects instructed to simulate mirror movements. We conclude that neuronal mechanisms in addition to bilateral corticomotoneuronal connections are at work in persistent mirror movements.     

Equipment for the quantification of motor performance for clinical purposes

An apparatus is described for the quantitative assessment of important parameters that characterise motor performance in normal subjects and in patients with different types of motor disorders. The apparatus has a handle that can be moved along a straight horizontal track either by the subject (to study voluntary movements) or by a torque motor (to study reflex activity). During voluntary movements the mass and friction of the mechanical part of the equipment are eliminated by feedback of the force exerted at the handle by the subject. The computer program that controls the apparatus gives a choice of four different tests that characterise different aspects of the motor system: the reflex organisation, the regulation of viscoelastic properties mediated in part by reflex activity, the control of fast goal-directed movements, and the performance in a tracking task. The results of a pilot study to the tracking behaviour of clumsy children show that the group of clumsy children differs from a group of normal children in the latency of the tracking response, in the ability to track high-frequency components and in the fact that clumsy children introduce relatively more frequency components in the response that are not present in the tracking signal.     

Effects of Gender and Age on Motor Exam in Typically Developing Children

Few studies have contrasted performance of typically developing boys and girls on standardized motor assessment. In the present study, developmental status of the motor system was assessed in 144 typically developing children (72 boys, 72 girls, ages 7–14), using the Physical and Neurological Examination for Subtle Signs (PANESS, Denckla, 1985). Four summary variables were examined: (1) Gaits and Stations, (2) Overflow, (3) Dysrythmia, and (4) Timed Movements. For most variables, gender differences were not significant; however significant gender effects were observed for some subtle signs (involuntary movements), gaits and stations, and timed patterned movements. In all instances, girls showed fewer subtle signs and were faster and more proficient than boys. Significant age-related changes were observed for some subtle signs (dysrythmia and overflow), and for timed movements. In contrast, by age 7, many of the skills assessed by the PANESS have reached “adult” level in typically developing children. Motor development appears to follow a different developmental course in girls than in boys; separate gender and age norms should be used in clinical assessment of motor function in children.     

Effects of gender and age on motor exam in typically developing children

Few studies have contrasted performance of typically developing boys and girls on standardized motor assessment. In the present study, developmental status of the motor system was assessed in 144 typically developing children (72 boys, 72 girls, ages 7-14), using the Physical and Neurological Examination for Subtle Signs (PANESS, Denckla, 1985). Four summary variables were examined: (1) Gaits and Stations, (2) Overflow, (3) Dysrythmia, and (4) Timed Movements. For most variables, gender differences were not significant; however significant gender effects were observed for some subtle signs (involuntary movements), gaits and stations, and timed patterned movements. In all instances, girls showed fewer subtle signs and were faster and more proficient than boys. Significant age-related changes were observed for some subtle signs (dysrythmia and overflow), and for timed movements. In contrast, by age 7, many of the skills assessed by the PANESS have reached “adult” level in typically developing children. Motor development appears to follow a different developmental course in girls than in boys; separate gender and age norms should be used in clinical assessment of motor function in children.     

Role of voluntary drive in encoding an elementary motor memory

Motor training consisting of repetitive thumb movements results in encoding of motor memories in the primary motor cortex. It is not known if proprioceptive input originating in the training movements is sufficient to produce this effect. In this study, we compared the ability of training consisting of voluntary (active) and passively-elicited (passive) movements to induce this form of plasticity. Active training led to successful encoding accompanied by characteristic changes in corticomotor excitability, while passive training did not. These results support a pivotal role for voluntary motor drive in coding motor memories in the primary motor cortex.     

Spontaneous facial motility in infancy: a 3D kinematic analysis

Early spontaneous orofacial movements have rarely been studied experimentally, though the motor experiences gained from these behaviors may influence the development of motor skills emerging for speech. This investigation quantitatively describes developmental changes in silent, spontaneous lip and jaw movements from 1 to 12 months of age using optically based 3D motion capture technology. Twenty-nine typically developing infants at five ages (1, 5, 7, 9, and 12 months) were studied cross-sectionally. Infants exhibited spontaneous facial movements at all ages studied. Several age-related changes were detected in lip and jaw kinematics: the occurrence of spontaneous movements increased, movement speed increased, the duration of movement epochs decreased and movement coupling among different facial regions increased. Additionally, evidence for stereotypic movements was not strong. The present findings suggest that, during the first year of life, early spontaneous facial movements undergo significant developmental change in the direction of skill development for speech.     

Time course and temporal order of changes in movement kinematics during learning of fast and accurate elbow flexions

Learning of a motor task, such as making accurate goal-directed movements, is associated with a number of changes in limb kinematics and in the EMG activity that produces the movement. Some of these changes include increases in movement velocity, improvements in end-point accuracy, and the development of a biphasic/triphasic EMG pattern for fast movements. One question that has remained unanswered is whether the time course of the learning-related changes in movement parameters is similar for all parameters. The present paper focuses on this question and presents evidence that different parameters evolve with a specific temporal order. Neurologically normal subjects were trained to make horizontal, planar movements of the elbow that were both fast and accurate. The performance of the subjects was monitored over the course of 400 movements made during experiments lasting approximately 1.5 h. We measured time-related parameters (duration of acceleration, duration of deceleration, and movement duration) and amplitude-related parameters (peak acceleration, peak deceleration, peak velocity), as well as movement distance. In addition, each subject’s reaction time and EMG activity was monitored. We found that reaction time was the parameter that changed the fastest and that reached a steady baseline earliest. Time-related parameters decreased at a somewhat slower rate and plateaued next. Amplitude-related parameters were slowest in reaching steady-state values. In subjects making the fastest movements, a triphasic EMG patterns was observed to develop. Our findings reveal that movement parameters change with different time courses during the process of motor learning. The results are discussed in terms of the neural substrates that may be responsible for the differences in this aspect of motor learning and skill acquisition. Received: 28 December 1998 / Accepted: 22 June 1999     

Differences in central control of m. biceps brachii in movement tasks and force tasks

Summary Motor-unit activity in m. biceps brachii during isometric flexion contractions has been compared with motor-unit activity during a slow voluntary movements against constant or increasing preloads and b flexion contractions while movements were imposed by a torque motor. Recruitment levels and firing frequency behaviour of the motor units were found to be very similar when torques were generated during isometric contractions and during the imposed movements. However, these characteristics of the biceps motor units were quite different during the slow voluntary movements. It is suggested that the central activation of the and/or motoneurone pools of m. biceps brachii is different for force tasks and slow movement tasks, even if the same torques are exerted and/or movements are made.     

Changes in elementary finger–hand functions over time in preschool children with spastic cerebral palsy

To examine the development of basic finger–hand motor capacity in a one-year follow-up experiment performed on young children with bilateral spastic cerebral palsy (CP). The maximal finger grip strength (FGMAX), the frequencies of the fastest voluntary isometric finger force changes (FGCHANGE) while holding an object, in addition to the finger (FTAP) and hand tapping frequencies (HTAP) were examined on two separate occasions in 30 children between the ages of three to six years with bilateral spastic CP (BCSP). The examinations were performed 12 months apart in order to test for improvements in the aforementioned functions. After a one-year period of time, the FGMAX, FGCHANGE and FTAP values increased by 10–15% in both hands (changes in FTAP values were not statistically significant), while the HTAP values remained unchanged. In regard to the normative samples obtained from children of this age period, the gap in the motor capacity of the fingers did not increase. We observed an improvement in the basic finger functions over a one-year period of time in preschool aged children diagnosed with spastic CP. Interestingly, the improvement proceeded at a similar rate to that observed in normally developing children. However, the fastest hand tapping movements (HTAP) did not improve during this one-year time interval. In addition, we observed that in young children with BSCP, there appears to be considerable potential for the development and reorganisation of the elementary finger functions that are requisite for object manipulation.     

Imagery of voluntary movement of fingers, toes, and tongue activates corresponding body-part-specific motor representations

We investigate whether imagery of voluntary movements of different body parts activates somatotopical sections of the human motor cortices. We used functional magnetic resonance imaging to detect the cortical activity when 7 healthy subjects imagine performing repetitive (0.5-Hz) flexion/extension movements of the right fingers or right toes, or horizontal movements of the tongue. We also collected functional images when the subjects actually executed these movements and used these data to define somatotopical representations in the motor areas. In this study, we relate the functional activation maps to cytoarchitectural population maps of areas 4a, 4p, and 6 in the same standard anatomical space. The important novel findings are 1). that imagery of hand movements specifically activates the hand sections of the contralateral primary motor cortex (area 4a) and the contralateral dorsal premotor cortex (area 6) and a hand representation located in the caudal cingulate motor area and the most ventral part of the supplementary motor area; 2). that when imagining making foot movements, the foot zones of the posterior part of the contralateral supplementary motor area (area 6) and the contralateral primary motor cortex (area 4a) are active; and 3). that imagery of tongue movements activates the tongue region of the primary motor cortex and the premotor cortex bilaterally (areas 4a, 4p, and 6). These results demonstrate that imagery of action engages the somatotopically organized sections of the primary motor cortex in a systematic manner as well as activating some body-part-specific representations in the nonprimary motor areas. Thus the content of the mental motor image, in this case the body part, is reflected in the pattern of motor cortical activation.     

The relationship between speed and amplitude of the fastest voluntary contractions of human arm muscles

Summary The relationship between the speed of the fastest possible voluntary contractions and their amplitude was examined for several hand- and forearm muscles under isometric and isotonic conditions.The consistent finding was the amplitude dependence of the speed of the fastest voluntary efforts: the larger the amplitude, the faster the contraction. The increase of the rate of rise of isometric tension or of the velocity of isotonic movements with rising amplitude was linear. The slope of this relationship was the same for three different hand- and forearm muscles examined.The duration of the contractions measured from onset to peak was approximately constant for all amplitudes. The duration of the EMG-burst recorded from the contracting muscle was similar as the time from onset to peak of the contraction.These results show that the skeleto-motor speed control system operates by adjusting the velocity of a contraction to its amplitude in such a way that the contraction time remains approximately constant. It is suggested that this type of speed control is a necessary requirement for the synchrony of synergistic muscle contractions.This work was supported by the Deutsche Forschungsgemeinschaft, SFB 70     

Analysis of evoked activity patterns of human thalamic ventrolateral neurons during verbally ordered voluntary movements

In the human thalamic ventralis lateralis nucleus the responses of 184 single units to verbally ordered voluntary movements and some somatosensory stimulations were studied by microelectrode recording technique during 38 stereotactic operations on parkinsonian patients. The tests were carried out on the same previously examined population of neurons classified into two groups, named A- and B-types according to the functional criteria of their intrinsic structure of spontaneous activity patterns. The evaluation of the responses of these units during functionally different phases of a voluntary movement (preparation, initiation, execution, after-effect) by means of the principal component analysis and correlation techniques confirmed the functional differences between A- and B-types of neurons and their polyvalent convergent nature. Four main conclusions emerge from the studies. (1) The differences of the patterns of A- and B-unit responses during the triggering and the execution phases of a voluntary movement indicate the functionally different role of these two cell types in the mechanisms of motor signal transmission. (2) The universal non-specific form of anticipatory A- and B-unit responses during the movement preparation and initiation of various kinds of voluntary movements reflect the integrative "triggering" processes connected with the processing and programming of some generalized parameters of a motor signal and not with the performance of a certain forthcoming motor act. (3) The expressed intensity of these "triggered" non-specific processes in the anterior parts of the ventralis lateralis nucleus indicates their relation not only to the motor but to the cognitive attentional functions forming a verbally ordered voluntary movement. (4) The appearance of the transient cross-correlations between the activities of adjacent A- and B-cells and also the synchronization of their 5 +/- 1 Hz frequency during and/or after motor test performances point to the contribution of these two populations to central mechanisms of the voluntary movement and the parkinsonian tremor. The functional role of two A- and B-cell types is discussed with references to the central mechanisms of verbally ordered voluntary movements and the parkinsonian tremor.     

Peripheral control of the cat's step cycle

Acute low spinal and curarized cats injected with noradrenergic agonists i.v. can elicit an efferent burst pattern which can be recorded in muscle nerve filaments and can be referred to as “fictive locomotion”. This study investigates the effect that feedback, arising from movements in the hip joint, can exert on the central network generating fictive locomotion. The central network is uncoupled from generating any active movements by curarization. The motor pattern could be entrained by applying sinusoidal hip movements, even when a very extensive denervation of the leg had been performed leaving only some of the muscles around the hip and the hip joint innervated. During flexion movements, efferents to different flexor muscles became active and during movements in the reverse direction (extension), efferents to extensors were active. With an increasing movement frequency the onsets of both flexor and extensor bursts were delayed in the movement cycle. The duration of the extensor bursts varied markedly with the movement cycle, whereas pure flexors changed less in burst duration. The frequency range within which the efferent burst activity was entrained in a strict 1:1 relation to the movement varied between 5 to 70% above and below the resting burst period. In preparations with a narrow 1:1 range, a “relative coordination” was encountered outside this range. The flexor burst duration was in these cases dependent on where in the hip movement cycle the bursts appeared.     

Effects of foreperiod duration on reflexive and voluntary responses to intense noise bursts

The question of whether a common mechanism underlies the facilitation of voluntary and reflexive reactions by a warning stimulus was investigated in two experiments. In both studies, the foreperiod preceding an intense noise burst was manipulated within and between blocks of trials. Previous reaction time experiments have shown that individuals respond fastest at the shortest foreperiod for between-block manipulations and fastest at the longest foreperiod when foreperiod duration is varied unpredictably from trial to trial. In the present research, this pattern was found for voluntary hand-grip responses, but acoustic startle blinks were facilitated at long foreperiods for both within- and between-block manipulations. Invariance of the trisynaptic postauricular reflex across foreperiod conditions was evidence against any general activation of low-level motor pathways by warning stimuli. Analyses of nonreflexive lid movements subsequent to startle blink suggested that inhibition of spontaneous blinking during the foreperiod may have contributed to the unexpected divergence between voluntary reactions and eyeblink reflexes.     

Peripheral control of the cat's step cycle. II. Entrainment of the central pattern generators for locomotion by sinusoidal hip movements during "fictive locomotion."

Acute low spinal and curarized cats injected with noradrenergic agonists i.v. can elicit an efferent burst pattern which can be recorded in muscle nerve filaments and can be referred to as "fictive locomotion". This study investigates the effect that feedback, arising from movements in the hip joint, can exert on the central network generating fictive locomotion. The central network is uncoupled from generating any active movements by curarization. The motor pattern could be entrained by applying sinusoidal hip movements, even when a very extensive denervation of the leg had been performed leaving only some of the muscles around the hip and the hip joint innervated. During flexion movements, efferents to different flexor muscles became active and during movements in the reverse direction (extension), efferents to extensors were active. With an increasing movement frequency the onsets of both flexor and extensor bursts were delayed in the movement cycle. The duration of the extensor bursts varied markedly with the movement cycle, whereas pure flexors changed less in burst duration. The frequency within which the efferent burst activity was entrained in a strict 1:1 relation to the movement varied between 5 to 70% above and below the resting burst period. In preparations with a narrow 1:1 range, a "relative coordination" was encountered outside this range. The flexor burst duration was in these cases dependent on where in the hip movement cycle the bursts appeared.     

Biocybernetic investigations of pursuit and posture motor control--a strategy for a detailed characterization of movement disorders in brain-damaged children

By means of a biocybernetic approach the pursuit and posture motor control of brain-damaged children with spastic hemiparesis and disturbed motor coordination of mild extent were investigated. The postural motor control system was loaded by pseudostochastic binary torque sequences applied to the wrist. The dynamics of this system were characterized on the basis of the parameters forearm displacement as well as surface-EMG of M. Biceps and Triceps (calculations of weight functions). The pursuit motor control was analyzed by a pursuit tracking method. By this way the motor capacity for fine and rough motor coordination, motor rhythm, motor adaptation, the maximal speed of movements and motor reaction time could be tested. Considering these results a characterization of movement control on different levels of motor regulation was possible (dynamics of muscular, spinal, and supraspinal components of motor control).     

Rate-dependent impairments in repetitive finger movements in patients with Parkinson's disease are not due to peripheral fatigue

Performance of repetitive finger movements is an important clinical measure of disease severity in patients with Parkinson's disease (PD) and is associated with a dramatic deterioration in performance at movement rates near 2 Hz and above. The mechanisms contributing to this rate-dependent movement impairment are poorly understood. Since clinical and experimental testing of these movements involve prolonged repetition of movement, a loss of force-generating capacity due to peripheral fatigue may contribute to performance deterioration. This study examined the contribution of peripheral fatigue to the performance of unconstrained index finger flexion movements by measuring maximum voluntary contractions (MVC) immediately before and after repetitive finger movements in patients with PD (both off- and on-medication) and matched control subjects. Movement performance was quantified using finger kinematics, maximum force production, and electromyography (EMG). The principal finding was that peak force and EMG activity during the MVC did not significantly change from the pre- to post-movement task in patients with PD despite the marked deterioration in movement performance of repetitive finger movements. These findings show that the rate-dependent deterioration of repetitive finger movements in PD cannot be explained by a loss of force-generating capacity due to peripheral fatigue, and further suggest that mechanisms contributing to impaired isometric force production in PD are different from those that mediate impaired performance of high-rate repetitive movements.     

Slowing fastest finger movements of the dominant hand with low-frequency rTMS of the hand area of the primary motor cortex

Neuroimaging studies suggest that the primary hand motor area and the cerebellum play a pivotal role in the control of finger tapping, but their differential contribution in this task is unknown. We used therefore repetitive transcranial magnetic stimulation (rTMS) in its virtual lesion mode (1 Hz, 10 min, 90% of motor threshold) to study the effects of transient disruption of the right lateral cerebellum (CB), the left primary hand motor area (M1), and the right brachial plexus (PL, control site) on various finger tapping tasks (paced finger tapping task: PFT; tapping with maximum speed: TAPMAX, and tapping with convenient speed: TAPCON) in healthy right-handed subjects. RTMS of the left M1 slowed finger tapping speed of the right hand in the TAPMAX task. This effect eliminated the right hand superiority in the TAPMAX task. In addition, rTMS of the left M1 resulted in slower tapping speeds for both hands during TAPCON. There were no other effects of rTMS on tapping speed or tapping variability. Findings indicate that M1 is essential for generating fastest finger movements.