Motor unit potential contribution to surface electromyography

The background of the bioelectric activity of muscle recorded from the surface of the skin (surface electromyography) in terms of the representation of single motor units of the underlying muscle(s) is not very well documented or understood. An insight into the composition of an electromyogram is essential for the proper interpretation of one of the most widely applied electrophysiological techniques. In the present paper, a study of the contribution of single motor unit potentials to the surface electromyogram is presented. To this end, the decline of different components of the motor unit potential with depth of the motor unit is quantified. Experimentally, the action potentials from motor units at several positions in the muscle were recorded by 30 skin surface electrodes. Simultaneous use of scanning electromyography provided information about the actual position and size of the motor unit. Observed linear log–log relationships between motor unit potential magnitudes and distance indicated the usefulness of a power function to describe the motor unit potential's dependence on recording distance. It is shown that different specific surface motor unit potential characteristics fall off differently with depth. The magnitude–distance relationship is shown to be dependent on the recording configuration (unipolar vs. bipolar recording, including the inter-electrode distance) and the chosen motor unit potential parameter (negative peak amplitude, positive peak amplitude and area).     

The effectiveness of 'nursing beds': a review of the literature

A literature search was conducted to identify 'nursing led in-patient units' where the nurse is the designated leader of the clinical team. The review concentrates on studies which have attempted to measure the impact of nursing-led in-patient units and reviews both the methodology and outcomes. Three major bodies of work were identified. Lydia Hall's evaluation of the Loeb Center for Nursing and Rehabilitation (USA) is reviewed in some detail. This work was the model for 'nursing beds' at the two Oxfordshire Nursing Development Units (UK) in the 1980s. Studies evaluating these centres are reviewed and reports of similar UK units discussed. A third body of work evaluates a nurse-managed critical care environment. Common features include a case mix based on nursing need with nurses having authority to admit and discharge patients. While results are generally favourable, with improved patient independence, fewer readmissions, lower mortality and cost savings reported in some or all of the studies, all studies reviewed demonstrate the difficulties of applying an experimental model to real life clinical services. Methodological limitations render firm conclusions difficult. Techniques adopted from studies in field settings, the so-called 'quasi-experiment', are advocated as a remedy, as is further study of the process of care in investigating this model of care delivery.     

Influence of peripheral afferents on cortical and spinal motoneuron excitability.

The objective of this study was to establish to what extent muscle, cutaneous, and joint afferents alter the excitability of spinal and cortical motor neurons. This question was examined by studying the impact of electrical stimulation of the second and third digits, the median nerve at the wrist, and the recurrent thenar motor branch on the F/H and magneto-electrical cortical motor responses (MEPs) of the thenar muscles. The firing frequencies of single F/H motor unit action potentials were unaltered by the foregoing conditioning peripheral stimuli. MEPs conditioned by motor threshold stimulation of the median nerve at the wrist or the recurrent motor branch were significantly increased in size at conditioning to test intervals of 50 to 80 milliseconds. No significant change in MEP size resulted from conditioning stimulation of the digital nerves. We conclude that muscle afferents were primarily responsible for the increase in MEP size. Conditioning stimuli may allow examiners to assess central motor conduction where it would otherwise be impossible.     

Effect of cognitive and motor tasks on postural stability in Parkinson's disease: a posturographic study.

To analyse the effect of concomitant cognitive or motor task performance on balance control in Parkinson's disease (PD), we performed a posturographic study in 24 PD patients and in 20 sex- and age-matched control subjects. Postural sway was measured with eyes open (EO) and eyes closed (EC) during quiet stance and during performance of calculation or motor sequence of thumb opposition to the other fingers. No difference of centre of foot pressure (COP) parameters was observed during quiet standing (either EO or EC) between patients and controls, but visual deprivation induced in both groups a worsening of postural stability. COP area was significantly increased in PD patients during dual task performance, whereas no difference of COP path and x-y axes was observed. The effects induced by the performance of cognitive or motor task were significantly more evident in PD patients with clinical evidence of postural instability (presence of prior falls in the history). This study demonstrates that dual task interference on postural control can be observed in PD patients during performance of cognitive as well as motor tasks. The balance deterioration during dual task performance was significantly enhanced in patients with history of prior falls. These findings have some implications for the strategies to be used in reducing the risk of fall in PD.     

Corneal D.C. recordings of slow ocular potential changes such as the ERG c-wave and the light peak in clinical work

A set-up for D.C. recordings of slow ocular potentials such as the c-wave of the electroretinogram (ERG) as well as the fast oscillation (FO), the light peak (LP) and the dark trough (DT) in both clinical and experimental work is described. It includes matched calomel half-cells connected by saline-agar bridges to a corneal contact lens on the eye and a reference chamber on the forehead, a low-drift differential-input D.C. amplifier, an A/D converter, a computer, a thermoprinter, a flexible disc memory, a plotter, and a device for light stimulation controlled by the computer.Examples of the usefulness of the set-up in clinical work are shown in the form of D.C. c-wave ERGs of normal subjects as well as of patients with vitelliform macular degeneration, choriocapillaris atrophy, and retinitis pigmentosa. The direct corneal recording of the FO and LP is demonstrated as well. The different origins of the standing potential (SP) of the eye, the ERG c-wave, the FO and the LP are reviewed briefly.     

Measuring oscillatory potentials: Fourier analysis

Studying the oscillatory potentials in diabetic retinopathy, the authors experienced several problems interpreting results of digital filtering. The main problem was the separation of the first potential from the a-wave, since their frequencies are within the same range. To improve the procedure of measuring implicit times and of calculating amplitudes, the filtering was started with a finite impulse response filter and followed by a fast Fourier transform. The power of the oscillatory potential was calculated by determining the dominant frequency in the Fourier transformed response and expressed in microwatts. A group of normal subjects was compared with a group of early diabetic retinopathy patients. It appears that even in pathological circumstances a quantitative expression of the oscillatory potential is possible.     

A slim needle-shaped multiwire microelectrode for intracerebral recording

The construction of a needle-shaped multiwire microelectrode is described. It can be made with simple mechanical tools. The presented electrode assembly consists of 12 insulated nichrome wires (core diameter 25 μm) which are embedded in epoxylite resin. The straight-cut wire tips are aligned lengthwise and have a relative spacing of 150 μm. Outer dimensions vary from 100 × 180 μm at the level of the 1st electrode channel, to 100 × 100 μm at the level of the 12th channel at the tip. The configuration of this electrode was determined by its application: the laminar analysis of evoked potentials in the cortex of the rat. However, the number of channels, the diameter of the (nichrome) wire which determines the surface area of these channels, and the channel spacing can be easily adjusted during construction to meet other experimental requirements, such as the recording of single-unit activity. The electrode which is composed of biocompatible materials is suited for the study of field potentials and multiple-unit activity, in both acute and chronic experiments, and can be used repeatedly. To demonstrate the performance of the electrode assembly, a depth profile of field potentials is presented, accompanied by the corresponding current source density distribution. The potentials were recorded in the somatosensory cortex of the rat following stimulation of the median nerve under ketamine anesthesia.     

Motor loss and swallowing difficulty after stroke: frequency, recovery, and prognosis.

Data relating to motor loss and swallowing difficulties in a community sample of 976 patients who suffered an acute stroke have been analysed. About 17% of patients seen within one week had no paralysis; at 6 months 48% of survivors had no paralysis and 9% had severe paralysis. The Motricity Index used to study motor loss related to functional loss and walking ability; it seems to be a simple valid measure of motor loss. Severe paralysis was associated with a high fatality rate, and only 6%-10% of survivors of an initially severe paralysis made a full recovery by 6 months. If severe persisted at 3 weeks, full recovery was not observed. Loss of sitting balance was associated with a poor outcome. Of conscious patients seen within one week, 14% choked on attempting to swallow and a further 28% had abnormal swallowing: this 42% of patients had a high fatality rate.     

Deleterious effects of the prone position in the full-term infant throughout the first year of life

Summary Seventy-one first-born infants who had been nursed in prone position since birth, were referred for motor assessment at 3 months, 5 months and 9 months. All infants were administered the same checklist of motor items, based on the Amiel-Tison Infant Neurological Evaluation and on the Brunet-Lézine Developmental Psychomotor Scale. Abnormalities in muscular shortening and delay in motor skills were found. These findings are critical as regards environmental influences on postural development, continuities in motor development and issues of early primary prevention. Early identification and follow-up programmes, including frequent changes in posture, are suggested in order to avoid abnormalities of motor behaviour and subsequently in postural patterns.     

Responses of human primary sensorimotor and supplementary motor areas to internally triggered unilateral and simultaneous bilateral one‐digit movements. A high‐resolution EEG study

We modelled the responses of human primary sensorimotor areas and supplementary motor area to simple, self-initiated unilateral and simultaneous bilateral middle finger movements using a novel high-resolution electroencephalography technology. The results support the view that these cortical motor areas are involved in parallel and present similar activity in the preparation, initiation, and execution of the contralateral and bilateral movements. Furthermore, the left primary sensorimotor area (dominant hemisphere) appears to be activated more than the right primary sensorimotor area during the preparation and performance of the ipsilateral movements.