Melissa C. Goldberg

Developmental dyspraxia is not limited to imitation in children with autism spectrum disorders

Impaired imitation of skilled gestures is commonly reported in autism. Questions, however, remain as to whether impaired imitation is associated with a more generalized deficit in performance of gestures consistent with a dyspraxia and whether the pattern of errors differs from that observed in typically developing children. To address these questions, praxis in 21 high-functioning children with autism spectrum disorders (ASD) was compared with 24 typically developing controls using a traditional approach in which performance was evaluated through detailed examination of error types. Children with ASD produced significantly fewer correct responses not only during Gesture to Imitation, but also during Gesture to Command and with Tool Use. The pattern of errors in ASD was similar to that of controls with spatial errors being most common in both groups; however, body-part-for-tool errors were more common in children with ASD, suggesting dyspraxia is not entirely attributable to motor deficits. The findings suggest that autism is associated with a generalized praxis deficit, rather than a deficit specific to imitation. In a developmental disorder such as autism, the findings may reflect abnormalities in frontal/parietal-subcortical circuits important for acquisition (i.e., learning) of sensory representations of movement and/or the motor sequence programs necessary to execute them.

Evidence for a deficit in procedural learning in children and adolescents with autism: Implications for cerebellar contribution

To examine the hypothesis that abnormalities in those cognitive functions for which cerebellar components have been implicated contribute to the pathophysiology of autism, tests of judgment of explicit time intervals and procedural learning were administered to 11 participants with autism and 17 age-and-IQ-matched controls. Results indicated that the group with autism demonstrated significant impairments in procedural learning compared with the group of controls. No significant difference in judgment of explicit time intervals was found. The data suggest that deficits in procedural learning may contribute to the cognitive and behavioral phenotype of autism; these deficits may be secondary to abnormalities in cerebellar-frontal circuitry.

Atypical motor and sensory cortex activation in attention-deficit/hyperactivity disorder: a functional magnetic resonance imaging study of simple sequential finger tapping.

BACKGROUND Attention-deficit/hyperactivity disorder (ADHD) has been shown to be associated with anomalous motor development, including excessive overflow movements. The neurological basis of these deficits has not been established. Functional magnetic resonance imaging (fMRI) was used to determine whether differences in brain activation during sequential finger tapping are present in children with ADHD compared with typically developing control subjects. METHODS Twenty-two right-handed children between 8 and 12 years old, 11 with ADHD and 11 typically developing control subjects closely matched for age and gender, performed self-paced sequential finger tapping during fMRI acquisition. RESULTS There were no significant between-group differences in speed of sequential finger tapping. The between-group whole-brain comparison showed greater magnitude of activation for control subjects than children with ADHD in the right superior parietal lobe during both right-handed and left-handed finger tapping. The region-of-interest analysis within Brodmann Area 4 revealed that children with ADHD showed a significantly smaller extent of fMRI activation in the primary motor cortex contralateral to the finger-sequencing hand. CONCLUSIONS Despite similar speed of sequential finger tapping, children with ADHD showed decreased contralateral motor cortex and right parietal cortex activation during both right-handed finger sequencing (RHFS) and left-handed finger sequencing (LHFS). The fMRI findings suggest that children with ADHD have anomalous development of cortical systems necessary for execution of patterned movements.

Deficits in the initiation of eye movements in the absence of a visual target in adolescents with high functioning autism

BACKGROUND We used ocular motor paradigms to examine whether or not saccades are impaired in individuals with high functioning autism (HFA). METHODS We recorded eye movements in patients with HFA (n=11), and in normal adolescents (n=11) on anti-saccade, memory-guided saccade (MGS), predictive saccade and gap/overlap tasks. RESULTS Compared with the normal subjects, patients with HFA had (1) a significantly higher percentage of directional errors on the anti-saccade task (63.2% versus 26.6%), (2) a significantly higher percentage of response suppression errors on a MGS task (60.3% versus 29.5%) and (3) a significantly lower percentage of predictive eye movements on a predictive saccade task. They also showed longer latencies on a MGS task and for all conditions tested on a gap/null/overlap task (fixation target extinguished before, simultaneously, or after the new peripheral target appeared). When the latencies during the gap condition were subtracted from the latencies in the overlap condition, there was no difference between patients and normals. CONCLUSIONS Abnormalities in ocular motor function in patients with HFA provide preliminary evidence for involvement of a number of brain regions in HFA including the dorsolateral prefrontal cortex (dlPFC) and the frontal eye fields (FEFs) and possibly the basal ganglia and parietal lobes.

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.

Motor persistence and inhibition in autism and ADHD

The present study compared performance of children with Attention-Deficit/Hyperactivity Disorder (ADHD) and high functioning autism (HFA) with that of controls on 4 tasks assessing 2 components of motor control: motor response inhibition and motor persistence. A total of 136 children (52 ADHD, 24 HFA, 60 controls) ages 7 to 13 years completed 2 measures of motor inhibition (Conflicting Motor Response and Contralateral Motor Response Tasks) and 2 measures of motor persistence (Lateral Gaze Fixation and NEPSY Statue). After controlling for age, IQ, gender, and basic motor speed, children with ADHD performed significantly more poorly than controls on the Conflicting Motor Response and Contralateral Motor Response Tasks, as well as on Statue. In contrast, children with HFA achieved lower scores than controls only on measures of motor persistence, with no concomitant impairment on either motor inhibition task. These results are consistent with prior research that has demonstrated relatively spared motor inhibition in autism. The findings highlight the utility of brief assessments of motor control in delineating the unique neurobehavioral phenotypes of ADHD and HFA.

Evidence of normal cerebellar control of the vestibulo-ocular reflex (VOR) in children with high-functioning autism.

The effect of “tilt-suppression” on post-rotatory vestibular nystagmus was investigated to assess the function of the caudal cerebellar vermis (lobules IX and X, or nodulus and uvula) in 13 school-age children with high-functioning autism (HFA) and 10 normal controls. Tilt-suppression of the vestibulo-ocular reflex (VOR) refers to the decreasing of the duration of post-rotatory vestibular nystagmus that occurs when the head is moved out of the plane in which it was located during the previous sustained constant-velocity rotation. The participant is rotated in a vestibular chair with the head upright and then the head is tilted forward just after the chair stops rotating. Such tilt-suppression is impaired with lesions of the cerebellar nodulus and portions of the uvula. Results show that children with HFA have normal post-rotatory nystasmus with the head upright and normal attenuation of post-rotatory nystagmus induced by head tilt. These behavioral findings suggest that lobules IX and X of the cerebellum are spared in high-functioning autism.

LEFT-RIGHT DIFFERENCES ON TIMED MOTOR EXAMINATION IN CHILDREN

Age-related change in the difference between left- and right-side speed on motor examination may be an important indicator of maturation. Cortical maturation and myelination of the corpus callosum are considered to be related to increased bilateral skill and speed on timed motor tasks. We compared left minus right foot, hand, and finger speed differences using the Revised Physical and Neurological Assessment for Subtle Signs (PANESS; Denckla, 1985); examining 130 typically developing right-handed children (65 boys, 65 girls) ages 7–14. Timed tasks included right and left sets of 20 toe taps, 10 toe-heel alternation sequences, 20 hand pats, 10 hand pronate-supinate sets, 20 finger taps, and 5 sequences of each finger-to-thumb apposition. For each individual, six difference scores between left- and right-sided speeded performances of timed motor tasks were analyzed. Left-right differences decreased significantly with age on toe tapping, heel-toe alternations, hand pronation-supination, finger repetition, and finger sequencing. There were significant gender effects for heel-toe sequences (boys showing a greater left-right difference than girls), and a significant interaction between age and gender for hand pronation-supination, such that the magnitude of the left-right difference was similar for younger, compared with older girls, while the difference was significantly larger for younger, compared to older boys. Speed of performing right and left timed motor tasks equalizes with development; for some tasks, the equalization occurs earlier in girls than in boys.

Examining the reinforcing value of stimuli within social and non-social contexts in children with and without high-functioning autism

One of the key diagnostic criteria for autism spectrum disorder includes impairments in social interactions. This study compared the extent to which boys with high-functioning autism and typically developing boys “value” engaging in activities with a parent or alone. Two different assessments that can empirically determine the relative reinforcing value of social and non-social stimuli were employed: paired-choice preference assessments and progressive-ratio schedules. There were no significant differences between boys with high-functioning autism and typically developing boys on either measure. Moreover, there was a strong correspondence in performance across these two measures for participants in each group. These results suggest that the relative reinforcing value of engaging in activities with a primary caregiver is not diminished for children with autism spectrum disorder.