Showing papers by "Mark Hallett published in 1988"

Hand cramps: Clinical features and electromyographic patterns in a focal dystonia

Abstract: We studied 19 patients with hand cramps, including writer's cramp, typist's cramp, piano, and guitar player's cramp. EMGs were recorded while patients performed the task triggering the cramps. Ten patients with dystonic cramps had EMGs with generalized muscle spasms with co-contraction of agonist and antagonist muscles. In three patients with simple cramps that involved one to three fingers, specific muscle groups showed co-contracting bursts that lasted longer than normal. The physiological abnormalities support the interpretation that hand cramp is a focal dystonia, characterized by both excessive muscle activity and defective fine motor control.

Postural adjustments associated with rapid voluntary arm movements. II. Biomechanical analysis.

Abstract: Normal subjects performed bilaterally symmetric rapid elbow flexions or extensions ("focal movements") while standing. Specific patterns of electromyographic activity in leg and trunk muscles ("associated postural adjustments") were seen for each type of movement. The biomechanical significance of these postural adjustments was analysed by means of the ground reaction forces and motion of the various body segments. Experimental data were compared with that from a theoretical model of the body consisting of a six segment kinetic chain with rigid links. Distinct patterns of the ground reaction forces with elbow flexion were opposite in direction to those seen with elbow extension. Movements of the various body segments were small and specific for a certain focal movement. Dynamic perturbations arising from the arm movement in an anteroposterior direction were found to be compensated by postural adjustments, whereas vertical perturbations were not compensated. The muscular activity acting about different joints in the different movements was found to correlate with the predictions of activity needed to compensate for net joint reaction moments arising from the focal movement. Motion of the various body segments could be understood as resulting from the interplay of the net reaction moments and the net muscular moments at the different joints. Dynamic postural requirements are accomplished by a precise active compensation initiated before the focal movement.

Dystonia with marked diurnal variation associated with biopterin deficiency

Abstract: Two pairs of siblings with severe dystonia with marked diurnal fluctuation had both reduced CSF concentration of biopterin and marked symptomatic improvement of the dystonia in response to levodopa. Whether the reduced concentration of biopterin reflects focal abiotrophy of biopterin-containing neurons or deficiency of biopterin synthesis is uncertain. A fifth individual, who had a systemic deficiency of biopterin synthesis, shared the features of reduced biopterin in CSF, marked diurnal variation in the degree of dystonia, and clinical improvement in response to levodopa. Generalized dystonia with marked diurnal fluctuation was therefore shared by the four patients in whom biopterin deficiency was limited to the CNS and the patient with systemic deficiency of biopterin.

Relevance of Stimulus Duration for Activation of Motor and Sensory Fibers: Implications for the Study of H-Reflexes and Magnetic Stimulation

Abstract: Electric stimuli with durations of 0.5-1.0 msec are optimal for studies of H-reflexes. It is more difficult to obtain H-reflexes with shorter duration stimuli or with magnetic stimulation. In order to understand this behavior, we studied the excitation thresholds for motor and sensory fibers in the ulnar, median and tibial nerves using both electric and magnetic stimulation. For short duration electrical stimuli (0.1 msec) the threshold for motor fibers is lower than for sensory fibers. For longer duration electric stimuli (1.0 msec) the threshold for sensory fibers is lower. For magnetic stimulation the threshold for motor fibers is much lower than for sensory fibers. Thus, stimulus duration is a critical parameter for sensory fiber excitation, and current magnetic stimulators are not optimal.

Noninvasive mapping of human motor cortex

Abstract: Human motor cortex was stimulated using brief, high-voltage electrical stimulation. Constant-voltage stimuli were delivered through a bipolar surface stimulator with the anode placed at multiple positions on the scalp and the cathode situated 2.5 cm anterior to the anode. Recordings were bilateral from the abductor pollicis brevis, tibialis anterior, and risorius. We averaged the amplitudes of three muscle responses obtained from stimulation of each scalp position and assigned the resultant value to that position. The findings in eight normal volunteers were similar and reproducible. The maximal responses of the right hand were obtained when stimulating over C3, of the left hand when stimulating over C4, of the right and left legs when stimulating over Cz, and of the right side of the mouth when stimulating over T3.

Stimulus artifact compensation using biphasic stimulation.

Abstract: The feasibility of using biphasic stimulation as a method of reducing stimulus artifact was explored in several different circumstances. Sensory and muscle evoked potentials were compared using monophasic and biphasic constant-current stimuli. The monophasic stimulus was a negative rectangular pulse with a duration of 0.1-0.2 msec. The biphasic stimulus was a negative rectangular pulse of 0.1-0.2 msec duration followed, after a variable delay, by a positive rectangular pulse of the same duration and variable amplitude. When the conducting distances were long, stimulus artifact did not disturb either monophasically or biphasically evoked potentials. When the conducting distances were short, stimulus artifact occurred with monophasic stimulation but could be diminished readily using biphasic stimulation. The method can be accomplished easily using standard instruments with dual stimulators.

Treatable Dystonia Presenting as Spastic Cerebral Palsy

Abstract: To the Editor.— Cerebral palsy is a disorder with nonprogressive motor impairment that begins in early infancy and is characterized by spasticity or involuntary movements.1 It is classified according to the primary motor disturbance present (spastic, extrapyramidal, hypotonic, and mixed). Approximately 65% of patients with cerebral palsy have the spastic type.2 The term does not imply a specific cause. Prematurity, anoxia, infection, trauma, and metabolic or other pathologic processes may be responsible in individual patients.

The first agonist and antagonist burst in patients with an upper motor neuron syndrome.

Abstract: Rapid elbow flexion movements were studied in patients with an upper motor neuron syndrome following a stroke The velocity of movements was slower than normal The initial bursts of electromyographic (EMG) activity in both the agonist and antagonist muscles were prolonged As in normal subjects, the first agonist burst increased in duration with larger movements, but it generally remained about 40 ms longer than normal The size of the first agonist burst also increased with larger movements A fixed linkage between burst duration and level of motor unit recruitment, together with a deficient corticospinal command, could explain the prolonged burst duration with preserved ability to modulate the burst