Upper limb function in children with attention-deficit/hyperactivity disorder (ADHD).

Upper limb function was investigated in children with ADHD using objective methods. We hypothesised that children with ADHD exhibit abnormal dexterity, force application during manipulation of a novel object, and movement rhythmicity. Two groups of age- and gender-matched children were investigated: 35 typically developing children (controls, 10.5 ± 0.4 years, 32M-3F) and 29 children (11.5 ± 0.5 years, 27M-2F) with formally diagnosed ADHD according to DSM-IV-TR criteria. Participants underwent a series of screening tests and tests of upper limb function while "off" medication. Objective quantification of upper limb function involved measurement of force during a grip and lift task, maximal finger tapping task, and maximal pinch grip. Acceleration at the index finger was also measured during rest, flexion and extension, and a postural task to quantify tremor. The Movement Assessment Battery for Children-2 (MABC-2) was also administered. Significant between-group differences were observed in movement rhythmicity, manipulation of a novel object, and performance of the MABC-2 dexterity and aiming and catching components. Children with ADHD lifted a novel object using a lower grip force (P = 0.036), and held the object with a more variable grip force (P = 0.003), than controls. Rhythmicity of finger tapping (P = 0.008) and performance on the dexterity (P = 0.007) and aiming and catching (P = 0.042) components of the MABC-2 were also significantly poorer in the ADHD group than controls. Movement speed, maximum pinch grip strength, and tremor were unaffected. The results of the study show for the first time that ADHD is associated with deficits in multiple, but not all domains of upper limb function.

History of Illicit Stimulant Use Is Not Associated with Long-Lasting Changes in Learning of Fine Motor Skills in Humans.

Little is known about the long-lasting effect of use of illicit stimulant drugs on learning of new motor skills. We hypothesised that abstinent individuals with a history of primarily methamphetamine and ecstasy use would exhibit normal learning of a visuomotor tracking task compared to controls. The study involved three groups: abstinent stimulant users (n = 21; 27 ± 6 yrs) and two gender-matched control groups comprising nondrug users (n = 16; 22 ± 4 yrs) and cannabis users (n = 16; 23 ± 5 yrs). Motor learning was assessed with a three-minute visuomotor tracking task. Subjects were instructed to follow a moving target on a computer screen with movement of the index finger. Metacarpophalangeal joint angle and first dorsal interosseous electromyographic activity were recorded. Pattern matching was assessed by cross-correlation of the joint angle and target traces. Distance from the target (tracking error) was also calculated. Motor learning was evident in the visuomotor task. Pattern matching improved over time (cross-correlation coefficient) and tracking error decreased. However, task performance did not differ between the groups. The results suggest that learning of a new fine visuomotor skill is unchanged in individuals with a history of illicit stimulant use.

Continuous passive movement does not influence motor maps in healthy adults.

Hand weakness following stroke is often associated with a reduced representation of the hand in the primary motor cortex. Meaningful sensory input can induce sensorimotor reorganization in the brain, but the after-effect of continuous passive motion (CPM) on the cortical representation is unknown. The purpose of this study was to determine whether repeated sessions of continuous passive movement of the thumb induce a lasting increase in the motor cortical representation of a thumb muscle in healthy adults. Thirteen right-handed healthy adults (mean age 24.3 ± 4.3 years) participated in the study. Single-pulse Transcranial Magnetic Stimulation (TMS) was delivered over the motor area of the target muscle (abductor pollicis brevis) before and/or after a thirty minute session of thumb CPM administered on three consecutive days. TMS was also delivered 5 days after cessation of the CPM intervention. The response to TMS (motor evoked potential) was recorded in the target muscle with surface EMG. Resting motor threshold (RMT), motor evoked potential amplitude at a specified intensity, and the area and volume of the cortical representation of the target muscle were measured. Thumb CPM had no significant effect on TMS parameters (p > 0.05 all measures) and performance of an attention task remained unchanged within and across CPM sessions. The results suggest that three sessions of repetitive passive thumb movement is not sufficient to induce a change in the cortical representation of the thumb and is unlikely to reverse the decreased representation of the affected hand following stroke.

Upper limb function is normal in patients with restless legs syndrome (Willis-Ekbom Disease).

OBJECTIVE: Restless legs syndrome, now called Willis-Ekbom Disease (RLS/WED), is a sensorimotor-related sleep disorder. Little is known of the effect of RLS/WED on motor function. The current study investigated upper limb function in RLS/WED patients. We hypothesised that RLS/WED patients exhibit subtle changes in tremor amplitude but normal dexterity and movement speed and rhythmicity compared to healthy controls. METHODS: RLS/WED patients (n=17, 59 ± 7 years) with moderate disease and healthy controls (n=17, 58 ± 6 years) completed screening tests and five tasks including object manipulation, maximal pinch grip, flexion and extension of the index finger (tremor assessment), maximal finger tapping (movement speed and rhythmicity assessment), and the grooved pegboard test. Force, acceleration, and/or first dorsal interosseus EMG were recorded during four of the tasks. RESULTS: Task performance did not differ between groups. Learning was evident on tasks with repeated trials and the magnitude of learning did not differ between groups. CONCLUSIONS: Hand function, tremor, and task learning were unaffected in RLS/WED patients. Patients manipulated objects in a normal manner and exhibited normal movement speed, rhythmicity, and tremor. SIGNIFICANCE: Further research is needed to assess other types of movement in RLS/WED patients to gain insight into the motor circuitry affected and the underlying pathophysiology.

Hand function is impaired in healthy older adults at risk of Parkinson's disease.

Abnormal substantia nigra morphology in healthy individuals, viewed with transcranial ultrasound, is a significant risk factor for Parkinson's disease. However, little is known about the functional consequences of this abnormality (termed 'hyperechogenicity') on movement. The aim of the current study was to investigate hand function in healthy older adults with (SN+) and without (SN-) substantia nigra hyperechogenicity during object manipulation. We hypothesised that SN+ subjects would exhibit increased grip force and a slower rate of force application compared to SN- subjects. Twenty-six healthy older adults (8 SN+ aged 58 ± 8 years, 18 SN- aged 57 ± 6 years) were asked to grip and lift a light-weight object with the dominant hand. Horizontal grip force, vertical lift force, acceleration, and first dorsal interosseus EMG were recorded during three trials. During the first trial, SN+ subjects exhibited a longer period between grip onset and lift onset (i.e. preload duration; 0.27 ± 0.25 s) than SN- subjects (0.13 ± 0.08 s; P = 0.046). They also exerted a greater downward force prior to lift off (-0.54 ± 0.42 N vs. -0.21 ± 0.12 N; P = 0.005) and used a greater grip force to lift the object (19.5 ± 7.0 N vs. 14.0 ± 4.3 N; P = 0.022) than SN- subjects. No between group differences were observed in subsequent trials. SN+ subjects exhibit impaired planning for manipulation of new objects. SN+ individuals over-estimate the grip force required, despite a longer contact period prior to lifting the object. The pattern of impairment observed in SN+ subjects shares similarities with de novo Parkinson's disease patients.