Biomedical subjects

H Topka

Publications and source records attributed to H Topka.

40 records · Page 3Linked to original sources

PubMed1992

Perioral reflexes in orofacial dyskinesia and spasmodic dysphonia.

In order to assess the clinical utility of trigemino-facial reflexes in lower facial muscles, we studied perioral reflexes to mechanical and electrical stimulation in 13 patients with spasmodic dysphonia and orofacial dyskinesia and in 7 healthy subjects. Mechanical stimulation of the upper lip of all patients and electrical stimulation of the infraorbital nerve of patients with orofacial dyskinesia elicited larger perioral reflexes than in controls. In the majority of patients, hyperexcitable perioral reflexes were accompanied by increased gain of the blink reflex. In 4 patients, however, trigemino-facial reflexes were enhanced selectively in either the perioral muscles or orbicularis oculi. Our findings suggest that the quantitative assessment of perioral reflexes may provide information about the excitability of brainstem interneurons in cranial dystonia that is complementary to blink reflex studies.

Blinking↗

PubMed1991

Magnetic stimulation of the human cerebral cortex, an indicator of reorganization in motor pathways in certain pathological conditions.

Basic principles of magnetic stimulation of biological tissues are reviewed. Noninvasive magnetic stimulation of the brain delivered over sensorimotor areas evokes movements and less commonly paresthesias in contralateral limbs. We have evaluated the maps of motor outputs in patients with (1) congenital mirror movements, which resulted in marked derangement of the map of outputs of distal hand muscles with enlarged and ipsilateral representations; (2) amputations, which resulted in plastic reorganization of motor outputs targeting muscles immediately proximal to the stump; (3) spinal cord injury, which also resulted in enlargement of the map of outputs targeting muscles proximal to the lesion level; and (4) hemispherectomy performed at an early age for intractable seizures, which resulted in the remaining hemisphere controlling ipsilateral arm muscles. These results demonstrate the potential for reorganization in motor systems following lesions in the peripheral as well as in the central nervous system.

Brain Mapping↗

PubMed1991

Reorganization of corticospinal pathways following spinal cord injury.

To assess changes in the relationship between cortical motor representation areas and their target muscles following spinal cord lesions, we studied motor evoked potentials (MEPs) to transcranial magnetic stimulation in six patients with complete spinal cord injuries at low thoracic levels and eight healthy subjects. Magnetic stimulation at rest activated a larger fraction of the motoneuron pool and evoked MEPs with shorter latencies from a larger number of scalp positions in muscles immediately rostral to the level of a spinal cord injury than in corresponding muscles in controls. The MEPs associated with maximal voluntary activation were not significantly different in the two groups. These results suggest enhanced excitability of motor pathways targeting muscles rostral to the level of a spinal transection, reflecting reorganization of motor pathways either within cortical motor representation areas or at the level of the spinal cord. The data do not allow the determination of the contribution of spinal or cortical mechanisms. However, they support the notion of a limited flexible relationship between primary motor cortex and its target muscles following alterations of normal input-output patterns.

Adult↗

PubMed1991

Leg paresthesias induced by magnetic brain stimulation in patients with thoracic spinal cord injury.

We studied the induction of leg paresthesias by magnetic stimulation of the brain in seven patients with thoracic T9-12 spinal cord injury and in four normal volunteers by delivering transcranial magnetic stimulation over scalp positions 1 cm apart with a Cadwell MES-10 magnetic stimulator and an 8-shaped magnetic coil at 100% stimulus intensity. We asked subjects to report sensations felt after each stimulus. In all normal subjects, magnetic stimulation evoked sensations described as tingling or a wave descending along the leg, usually accompanied by EMG responses in leg muscles. In three of the seven patients, stimulation evoked sensations of tingling, numbness, touch, or a wave descending along the leg, lasting up to 10 seconds and referred to different parts of the legs and toes. In the patients, sensations were felt more distally the closer the site of stimulation was to the midline. Patients with leg paresthesias had less motor reorganization in abdominal muscles than those without paresthesias. These findings suggest that portions of the cortical representation areas for body parts deafferented by a complete spinal cord injury can remain related to those body parts for up to several years. A central origin of these paresthesias is probable.

Brain↗