Biomedical subjects

T W Findley

Publications and source records attributed to T W Findley.

39 records · Page 3Linked to original sources

PubMedDate not supplied

Facilitatory effect of thinking about movement on motor-evoked potentials to transcranial magnetic stimulation of the brain.

Two experiments using transcranial magnetic stimulation (TMS) were undertaken to investigate facilitatory effects of thinking about a specific movement without voluntary discharges on motor-evoked potentials (MEP). First, surface electromyographic (EMG) responses from the abductor pollicis brevis were recorded with maximal stimulator output in the three conditions: the muscle being at rest, contracting with 10% of maximal muscle activity, and with the subject "only thinking" about thumb abduction (nine subjects). Median value of MEP amplitudes during "only thinking" was twice that at rest (P = 0.008) and one-half that during voluntary contraction (P = 0.008). Second, needle EMG responses from the first dorsal interosseus were compared at rest, during thinking about index finger abduction, and during TMS at threshold intensity. Four normal subjects were tested with stimulation of each cerebral hemisphere for a total of eight tests. The number of detectable MEP responses of 20 stimuli to one hemisphere was counted for each condition of rest or thinking. The mean MEP response rate during thinking (58%) was higher than that at rest (12%) (P < 0.005). These results demonstrate that thinking about a specific movement has facilitatory effects on MEP and that the degree of facilitation in thinking is smaller than in voluntary contraction.

Adult↗

PubMedDate not supplied

Reciprocal inhibition in the forearm during voluntary contraction and thinking about movement.

The regulatory mechanism for the interaction of agonist and antagonist muscles is not still clear. In these studies we investigated reciprocal inhibition during voluntary contraction and thinking about movement by using transcranial magnetic stimulation (TMS) and the H reflex technique. Magnetic stimuli, with intensities 10% above threshold, were delivered at the scalp under 3 experimental conditions; at rest, during voluntary isometric weak contraction and during thinking about movement. Surface EMG responses were taken from extensor carpi radialis (ECR) and flexor carpi radialis (FCR) muscles in 14 normal subjects. Inhibitions of antagonist muscles induced by thinking about agonist movement occurred in 8 ECR and 10 FCR muscles, but most of them were not statistically significant. H reflexes were obtained from the FCR muscles in 10 normal subjects under the same conditions. Voluntary wrist extension and thinking about wrist extension produced inhibition of the H reflex in the FCR muscles. Reciprocal inhibition of antagonist muscles may occur at the cortical and spinal cord levels. The excitability of motoneurons has effects on the H reflex amplitude. Motor evoked potential (MEP) response to TMS might be affected by the combination of input from the motor cortex and the spinal cord. TMS may evoke simultaneous facilitatory and inhibitory volleys to antagonist muscles. This may explain why the inhibitions in the TMS study were weaker than those in the H reflex study.

Adult↗

PubMedDate not supplied

Muscle fiber conduction velocity (MFCV) after fatigue in elderly subjects.

The changes in muscle fiber conduction velocity (MFCV) and median frequency (MDF) during and after muscle fatigue were investigated in 9 younger (mean age: 29.3) and 7 elderly (mean age: 72.0) healthy subjects to determine if age has any effect on them. The surface EMG of the abductor digiti minimi muscle was examined at 50% of maximal voluntary contraction (MVC) during a prefatigue session. The subjects were instructed to continue applying maximal force until the force declined to 50% MVC. EMG signals were measured during brief subsequent contractions at 50% MVC until 60 minutes after fatigue as a postfatigue session. The decrement in MFCV and MDF at 50% MVC before and after fatigue was 73.4%, 67.3% in the younger and 71.2%, 66.7% in the elderly subjects, respectively. MFCV and MDF recovered to initial value after fatigue more slowly in the elderly subjects (recovery time: elderly: MFCV 6.0 min., MDF 6.0 min.; younger: MFCV 2.77 min., MDF 3.00 min.) (P < 0.05, Mann-Whitney test). The over-shooting recovery phase was recognized in both age groups, but the elderly subjects had a smaller and shorter one. The slower recovery in the elderly suggested that they possibly had less potential to recovery the membrane potential propagation, metabolic capacity and more type 1 fiber composition. The smaller and shorter overshooting in the elderly might be due to less increase of muscle swelling and/or less membrane hyperpolarization.

Adult↗