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B L Day

Publications and source records attributed to B L Day.

114 records · Page 7Linked to original sources
PubMed1982

Manual motor performance in a deafferented man.

We have studied manual motor function in a man deafferented by a severe peripheral sensory neuropathy. Motor power was almost unaffected. Our patients could produce a very wide range of preprogrammed finger movements with remarkable accuracy, involving complex muscle synergies of the hand and forearm muscles. He could perform individual finger movements and outline figures in the air with high eyes closed. He had normal pre- and postmovement EEG potentials, and showed the normal bi/triphasic pattern of muscle activation in agonist and antagonist muscles during fast limb movements. He could also move his thumb accurately through three different distances at three different speeds, and could produce three different levels of force at his thumb pad when required. Although he could not judge the weights of objects placed in his hands without vision, he was able to match forces applied by the experimenter to the pad of each thumb if he was given a minimal indication of thumb movement. Despite his success with these laboratory tasks, his hands were relatively useless to him in daily life. He was unable to grasp a pen and write, to fasten his shirt buttons or to hold a cup in one hand. Part of hist difficulty lay in the absence of any automatic reflex correction in his voluntary movements, and also to an inability to sustain constant levels of muscle contraction without visual feedback over periods of more than one or two seconds. He was also unable to maintain long sequences of simple motor programmes without vision.

Adult↗
PubMed1982

Accurate repositioning of the human thumb against unpredictable dynamic loads is dependent upon peripheral feed-back.

1. The strategy of accurate movement of the human thumb has been studied in nine subjects. An open-loop hypothesis, which states that a new final position is defined by re-setting the agonist/antagonist spring constants, was tested2. Subjects were trained to flex the top joint of the thumb rapidly through 20 deg in about a third of a second from a fixed starting position against a load. Occasionally, and unpredictably, the viscous friction of the load was altered prior to it's being moved. The spring hypothesis predicts that such a change in load should have no effect on final position accuracy.3. Under normal conditions no final position error developed when the viscous friction was increased. A small overshoot occurred when the viscous friction was decreased.4. The electromyogram recorded from surface electrodes over the belly of flexor pollicis longus in the forearm revealed an increase in activity in response to an increase in viscous friction and a decrease in activity when the viscous friction was reduced.5. When the joint and cutaneous afferents from the thumb were anaesthetized, the e.m.g. response to a change in viscous friction was severely attenuated and consistent final position errors developed.6. Even though the compensatory open-loop muscle properties went some way towards maintaining accuracy, the change in final position error that occurred as a result of thumb anaesthesia correlated well (r = 0.84) with the amount of muscle e.m.g. response that was lost.7. The latency of the e.m.g. response to a change in viscous friction was compared to that of a voluntary response by asking the subject to push down or let go upon perception of the load change. Approximately the first 100 ms of the e.m.g. response was unaffected by the voluntary intervention of the subject.8. We conclude that the spring hypothesis does not explain human thumb movement. It is argued that the long-latency stretch reflex machinery is responsible for some automatic compensation for unexpected interference with movement.

Adult↗
PubMedDate not supplied

The corticomotoneurone connection is normal in Parkinson's disease.

Voluntary movements in Parkinson's disease are initiated and executed slowly. It is assumed that the motor cortex and its output pathway are intact and that bradykinesia is due to abnormal motor commands delivered to a normal corticospinal system. We have tested this assumption using electrical stimulation of the motor cortex through the scalp in three patients with severe Parkinson's disease, studied during fluctuations from relatively normal mobility when receiving drugs (ON) to severe bradykinesia when not receiving drugs (OFF). Thresholds and latencies for motor cortex stimulation to excite thumb flexor muscles and the resulting fast mechanical responses were the same in both ON and OFF conditions, even though the patients were unable to execute fast thumb flexion movements voluntarily when OFF. We conclude that the excitability and conduction velocity of the corticospinal motor pathways are normal in Parkinson's disease.

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