PubMed Health⌕ Search

Biomedical subjects

D M Halliday

Publications and source records attributed to D M Halliday.

15 recordsLinked to original sources
PubMed1999

Coherent cortical and muscle discharge in cortical myoclonus.

There is increasing evidence in man that the cortical drive to motor neurons is rhythmic. This oscillatory drive may be exaggerated in patients with cortical myoclonus. Spectral analysis of surface bipolar EEG and EMG activity was performed in eight such patients. Only three cases had evidence of giant cortical evoked potentials or a cortical correlate on back-averaging at the time of study. In six subjects, significant coherence between contralateral and vertex EEG and EMG was observed in ranges similar to that previously reported for normal subjects (15-30 and 30-60 Hz). Three out of these six subjects also had significant coherence at higher frequencies (up to 175 Hz). All eight patients had a correlate in the cumulant density estimate between EEG and contralateral EMG. EMG lagged EEG by about 14, 25 and 35 ms for the muscles of the forearm, hand and foot, respectively. These delays were estimated from the slope of the phase curves and the timing of the peaks in the cumulant density estimates, and are appropriate for conduction in fast pyramidal pathways. The results provide clear evidence of a cortical drive synchronizing muscle discharge over a broad range of frequencies in patients with cortical myoclonus. Fourier analysis is a promising technique in the diagnosis and investigation of such patients.

Adolescent↗
PubMed1998

Identification of patterns of neuronal connectivity--partial spectra, partial coherence, and neuronal interactions.

The cross-correlation histogram has provided the primary tool for inferring the structure of common inputs to pairs of neurones. While this technique has produced useful results it not clear how it may be extended to complex networks. In this report we introduce a linear model for point process systems. The finite Fourier transform of this model leads to a regression type analysis of the relations between spike trains. An advantage of this approach is that the full range of techniques for multivariate regression analyses becomes available for spike train analysis. The two main parameters used for the identification of neural networks are the coherence and partial coherences. The coherence defines a bounded measure of association between two spike trains and plays the role of a squared correlation coefficient defined at each frequency lambda. The partial coherences, analogous to the partial correlations of multiple regression analysis, allow an assessment of how any number of putative input processes may influence the relation between any two output processes. In many cases analytic solutions may be found for coherences and partial coherences for simple neural networks, and in combination with simulations may be used to test hypotheses concerning proposed networks inferred from spike train analyses.

Animals↗
PubMed1998

Using electroencephalography to study functional coupling between cortical activity and electromyograms during voluntary contractions in humans.

Previous studies of neuronal oscillations in sensorimotor cortex in humans and primates have observed rhythmic 15-30 Hz activity, which is correlated with motor output. In humans, this work has been limited to magnetic recordings. In the present study we investigate if similar results can be obtained using electroencephalography (EEG). EEG recordings were made from over the sensorimotor cortex of five adult subjects who performed repeated periods of maintained wrist extension and flexion. Coherence analysis between EEG and electromyogram (EMG) recordings from these muscles revealed correlation in the 15-30 Hz range, with a synchronous correlation structure which matches that previously observed in humans and in paired cortical recordings from primates. We conclude that EEG is equally efficient at investigating functional aspects of these cortical rhythms during voluntary movement in humans.

Adult↗
PubMed1998

Physiological tremor in human jaw-muscle system.

Small, quasi-rhythmical tremor of the jaw occurs at rest and during voluntary movements. In peripheral limbs, tremor consists of a component due to mechanical resonance properties of the system, and a neurogenic component mediated by a central pacemaker or neural loops. The present study attempted to determine if these components were present in jaw tremor measured with a position transducer held lightly between the incisors. When weights were suspended from the mandible, the tremor frequency was unaltered; sharp taps delivered to the jaw did not elicit any kind of damped oscillations of the system. These findings indicated the absence of mechanical resonance in the system. No correlation of the tremor signal with the electrocardiogram was found. However, a strong correlation was found between the rectified electromyographic signals recorded over the masseter muscles and the tremor signal, where the electromyographic signal preceded jaw movement by 20-30 msec. Frequency-domain analysis also showed positive peaks in a majority of coherence functions between electromyographic and tremor signals. These results suggested a strong neurogenic component of the tremor.

Adult↗
PubMed1998

Generation and characterization of correlated spike trains.

A framework within which to generate and characterize populations of correlated spike trains is presented. Spike trains are generated using integrate to threshold and fire type encoders. Spectral analysis techniques form the basis for specifying the strength of correlation within the population. To accurately specify weak correlation, a combined coherence estimate is formed between several independent pairs of spike trains from a population. The aim is to produce populations of spike trains which have a realistic stochastic correlation structure and which can be used to explore the role of correlated neuronal discharge in information processing in neuronal systems.

Computer Simulation↗
PubMed1998

Abnormal motor unit synchronization of antagonist muscles underlies pathological co-contraction in upper limb dystonia.

The aim of this study was to examine the pathophysiological mechanisms underlying co-contraction in patients with dystonia (n = 6) and writer's cramp (n = 5). Multi-unit needle and surface EMGs were recorded from extensor carpi radialis (ECR) and flexor carpi radialis (FCR) muscles during motor tasks that elicited dystonia or writer's cramp. The EMGs from ECR and FCR were recorded simultaneously and analysed using cross-correlation analysis. Similar recordings were obtained from healthy age- and sex-matched control subjects (n = 8). Despite co-contraction of the muscles, cross-correlograms from the healthy subjects did not reveal evidence of motor unit synchronization. Cross-correlograms from the dystonic subjects revealed a central peak with a median duration of 37 ms, indicating broad-peak motor unit synchronization. Cross-correlograms from patients with writer's cramp were either flat or modulated by a 11-12-Hz tremor. Frequency-domain analysis of ECR and FCR EMGs demonstrated significant coherence in the patients with dystonia and writer's cramp. These results indicate that co-contraction in dystonia is neurophysiologically distinct from voluntary co-contraction and is produced by abnormal synchronization of presynaptic inputs to antagonist motor neuron pools. ECR and FCR co-contraction in writer's cramp may be a compensatory process under voluntary control.

Adolescent↗
PubMed1997

A review of recent applications of cross-correlation methodologies to human motor unit recording.

This article reviews some recent applications of time and frequency domain cross-correlation techniques to human motor unit recording. These techniques may be used to examine the pre-synaptic mechanisms involved in control of motoneuron activity during on-going motor tasks in man without the need for imposed and artificial perturbations of the system. In this review we examine, through several examples, areas in which insights have been gained into the basic neurophysiological processes that bring about motoneuron firing in man and illustrate how these processes are affected by central nervous system pathology. We will demonstrate that synchronization and coherence may be revealed between human motor unit discharges and give examples that support the hypothesis that these phenomena are generated by activity in a focused common corticospinal input to spinal motoneurons. Disruption of central motor pathways due to diseases of the nervous system leads to pathophysiological alterations in the activity of these pre-synaptic motoneuron inputs that can be revealed by cross-correlation analysis of motor unit discharges. The significance of these studies and outstanding questions in this field are discussed.

Electromyography↗
PubMed1997

An extended difference of coherence test for comparing and combining several independent coherence estimates: theory and application to the study of motor units and physiological tremor.

Recently there has been an increase in the use of spectral methods for the analysis of experimental data. These analytical methods allow the study of interactions between simultaneously recorded signals and are particularly suited to the study of systems displaying rhythmic behaviour. A useful parameter in this context is the coherence function which provides a bounded measure of linear association between two signals. In this report we introduce two new techniques for dealing with an arbitrary number of independent coherence estimates. The first technique provides a test to compare the coherence estimates for statistically significant differences. The second allows the original coherence estimates to be combined, or 'pooled' into a single representative estimate. These two measures, taken together, provide a powerful tool for characterising and summarising the correlations within data sets. Applications of the techniques are illustrated by analysing the interactions between single motor unit discharges and finger tremor, and between pairs of motor unit discharges in human subjects.

Humans↗
PubMed1995

Synchronization between motor cortex and spinal motoneuronal pool during the performance of a maintained motor task in man.

1. Simultaneous recordings of cortical activity, recorded as the magnetoencephalogram (MEG), and the electromyogram (EMG) of the ipsilateral and contralateral first dorsal interosseous muscles (1DI) were made during maintained voluntary contractions. 2. The MEG recorded from a localized region of the sensorimotor cortex of the dominant hemisphere was coherent with the EMG from the contralateral 1DI muscle over a limited band of frequencies. The peak coherence was confined largely within the beta range of cortical activity (13-35 Hz). Significant cortical activity at 10 Hz and 40-50 Hz was not correlated with motor output. The MEG and EMG from the ipsilateral 1DI muscle were uncorrelated at all frequencies. 3. Significant coherence between the MEG and the EMG was associated with synchronous behaviour between the MEG and EMG in the time domain. 4. The results demonstrate that synchronized cortical activity contributing to MEG activity within the beta range of frequencies during maintained voluntary contractions is coupled to motor output at frequencies of motor-unit activity associated with motor-unit synchronization. This observation provides further evidence for the involvement of cortical neurones in the generation of motor-unit synchronization. 5. We suggest that the coherence between MEG and contralateral EMG observed during maintained isometric contractions may provide an example of binding within the motor system.

Adult↗
PubMed1993

The frequency content of common synaptic inputs to motoneurones studied during voluntary isometric contraction in man.

1. The discharges of pairs of individual motor units were recorded from intrinsic hand muscles in man. Single motor unit recordings were obtained either when both members of the motor unit pair were within first dorsal interosseous muscle (1DI:1DI recordings) or where one motor unit was within 1DI and the other in second dorsal interosseous muscle (1DI:2DI recordings). The pairs of motor unit spike trains were cross-correlated in the time domain and the results compared to those of coherence analysis performed on the same spike train data. Central peaks were present in the cross-intensity functions, indicating the presence of common synaptic input to the motoneurone pair. Coherence analysis of these data indicated significant association between motor unit firing in the frequency ranges 1-12 and 16-32 Hz. 2. Analysis of sequential non-overlapping segments of data recorded from individual motor unit pairs, demonstrated that both the central cross-intensity peak and coherence in the frequency bands 1-12 and 16-32 Hz were consistent features throughout a long recording. In these sequential recordings, the size of the central cross-intensity peak and the maximal value of coherence in the frequency band 16-32 Hz covaried from segment to segment. Analysis of the entire population of motor unit pairs confirmed a positive relationship between the magnitude of peak coherence and the size of the central cross-intensity peak. 3. Voluntary sinusoidal co-modulation of the firing rates of pairs of individual motor units recorded from within 1DI was found to produce significant values of coherence corresponding to the frequency of the common modulation. However, firing rate co-modulation was not found to affect either the size of the central cross-intensity peak or the maximum value of coherence in the frequency band 16-32 Hz. 4. Pairs of single motor units were recorded from within 1DI and biceps brachii muscles of healthy subjects. The number and size of the central cross-intensity peaks and coherence peaks detected were compared for the two muscles. The incidence and size of central cross-intensity peaks and the incidence and magnitude of 16-32 Hz coherence peaks were both found to be greater for 1DI recordings when compared to biceps brachii recordings. 5. Single motor unit recordings were made from the intrinsic hand muscles of a patient with severe peripheral deafferentation. Time- and frequency-domain analysis of these recordings revealed cross-intensity peaks and frequency bands of coherence similar to those seen in healthy subjects.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1993

Detection of weak synaptic interactions between single Ia afferent and motor-unit spike trains in the decerebrate cat.

1. Spike trains from identified single Ia afferents from soleus and lateral gastrocnemius muscles were recorded (while 'in continuity' with the spinal cord) simultaneously with single-motor-unit EMG spike trains from the same muscles in decerebrate cats. 2. A total of 143 Ia afferent-motor-unit pairs were examined for the presence of correlated activity between the Ia afferent and motor-unit and between the motor-unit and Ia afferent. Four types of correlation were identified on the basis of the cross-intensity function estimated for individual Ia afferent-motor-unit pairs. These correlations were attributed to the absence or presence of a central Ia afferent-motoneurone interaction or a peripheral motor-unit-muscle spindle interaction. 3. In addition to the cross-correlation-based second-order cross-intensity function, third-order cumulants were defined and used further to investigate Ia afferent-motor-unit interactions. A third-order cumulant density-based approach to signal processing offers improved signal-to-noise ratios, compared with the traditional product density approach, for parameters characterizing certain kinds of linear processes as well as a description of non-linear interactions. Two classes of third-order relations were described. One class was associated with a strong central connection and the other with a weak central connection. 4. Third-order cumulants estimated for Ia afferent-motor-unit pairs with significant second-order central correlations were able to detect a period of decreased motoneuronal excitability. In addition, temporal summation prior to spike initiation could be identified in cases where the afferent discharge was suitably high. 5. Third-order cumulants estimated for Ia afferent-motor-unit pairs in which no significant second-order central correlation existed identified the presence of weak synaptic interactions. It is argued that these interactions result from the summation from the recorded Ia afferent discharge and other spontaneous synaptic inputs to the motoneurone. 6. The results of the second-order cross-intensity analysis of Ia afferent-motor-unit interactions, combined with those from the third-order cumulant density analysis, showed that 77% of the recorded afferents had a detectable influence on motor-unit behaviour. 7. The results of this study suggest that the third-order cumulant, based on the analysis of spike trains, will provide a useful tool for detecting synaptic interactions not found by the use of the second-order cross-correlation histogram alone, and may also be used to estimate the time course of post-spike depression in motoneurones, as well as other non-linear regions of motoneurone membrane trajectory.

Action Potentials↗
PubMed1989

Fusimotor mechanisms determining the afferent output of muscle spindles.

There is both direct and indirect evidence that stretch activation occurs in the dynamic bag1 fibres of the mammalian muscle spindle and that it is responsible for maintaining the high sensitivity of primary sensory endings in stretches great enough to break the resting actomyosin bonds responsible for the short-range stiffness of muscle fibres. However the direct observations of dynamic bag1 fibre behaviour during stretching were made on damaged fibres and during very slow stretches. Preliminary results of experiments employing faster stretches of intact muscle spindles are reported here. An image processing system is being developed to automate and facilitate analysis of sarcomere movements during stretch, release and activation of intrafusal fibres. Unequivocal evidence confirming the development of stretch activation has not yet been found. Boyd (1986a) believed that static bag2 and chain fibres are controlled by separate populations of static gamma motoneurones, while accepting that there is some degree of common innervation. His evidence and the functional implications are discussed.

Animals↗
PubMed1989

A framework for the analysis of neuronal networks.

The object of this work is to consider the application of some methods of spike train analysis that are not widely known, and are concerned with the description of the interaction between spike trains and the determination of causal connections between them. The notation and terminology follow conventions established in the statistical literature. The examples given are based on in-continuity recordings of the spontaneous activity of single Ia afferents from the soleus muscle and single motor units from the same muscle. Cumulant densities are shown to be simple extensions of the traditional cross-correlation methods, and are useful in characterizing the pattern of activity in one spike train that influences that in another, and to reveal interactions between spike trains that would not be apparent from the correlation histogram alone. Parameters based on the Fourier transforms of the spike trains are shown to be useful in determining timing relations between them, and in inferring patterns of connectivity not possible by correlation methods alone.

Action Potentials↗