Biomedical subjects

David M Halliday

Publications and source records attributed to David M Halliday.

4 recordsLinked to original sources

PubMed2006

Changes in EMG coherence between long and short thumb abductor muscles during human development.

In adults, motoneurone pools of synergistic muscles that act around a common joint share a common presynaptic drive. Common drive can be revealed by both time domain and frequency domain analysis of EMG signals. Analysis in the frequency domain reveals significant coherence in the range 1-45 Hz, with maximal coherence in low (1-12 Hz) and high (16-32 Hz) ranges. The high-frequency range depends on cortical drive to motoneurones and is coherent with cortical oscillations at approximately 20 Hz frequencies. It is of interest to know whether oscillatory drive to human motoneurone pools changes with development. In the present study we examined age-related changes in coherence between rectified surface EMG signals recorded from the short and long thumb abductor muscles during steady isometric contraction obtained while subjects abducted the thumb against a manipulandum. We analysed EMG data from 36 subjects aged between 4 and 14 years, and 11 adult subjects aged between 22 and 59 years. Using the techniques of pooled coherence analysis and the chi(2) difference of coherence test we demonstrate that between the ages of 7 and 9 years, and 12 and 14 years, there are marked increases in the prevalence and magnitude of coherence at frequencies between 11 and 45 Hz. The data from subjects aged 12-14 years were similar to those obtained from adult controls. The most significant differences between younger children and the older age groups were detected at frequencies close to 20 Hz. We believe that these are the first reported results demonstrating significant late maturational changes in the approximately 20 Hz common oscillatory drive to human motoneurone pools.

Adolescent↗

PubMed2006

Neural spike train synchronization indices: definitions, interpretations, and applications.

A comparison of previously defined spike train syncrhonization indices is undertaken within a stochastic point process framework. The second-order cumulant density (covariance density) is shown to be common to all the indices. Simulation studies were used to investigate the sampling variability of a single index based on the second-order cumulant. The simulations used a paired motoneurone model and a paired regular spiking cortical neurone model. The sampling variability of spike trains generated under identical conditions from the paired motoneurone model varied from 50% to 160% of the estimated value. On theoretical grounds, and on the basis of simulated data a rate dependence is present in all synchronization indices. The application of coherence and pooled coherence estimates to the issue of synchronization indices is considered. This alternative frequency domain approach allows an arbitrary number of spike train pairs to be evaluated for statistically significant differences, and combined into a single population measure. The pooled coherence framework allows pooled time domain measures to be derived, application of this to the simulated data is illustrated. Data from the cortical neurone model is generated over a wide range of firing rates (1-250 spikes/s). The pooled coherence framework correctly characterizes the sampling variability as not significant over this wide operating range. The broader applicability of this approach to multielectrode array data is briefly discussed.

Action Potentials↗

PubMed2004

Coexistence of gamma and high-frequency oscillations in rat medial entorhinal cortex in vitro.

High frequency oscillations (> 80-90 Hz) occur in neocortex and hippocampus in vivo where they are associated with specific behavioural states and more classical EEG frequency bands. In the hippocampus in vitro these oscillations can occur in the absence of pyramidal neuronal somatodendritic compartments and are temporally correlated with on-going, persistent gamma frequency oscillations. Their occurrence in the hippocampus is dependent on gap-junctional communication and it has been suggested that these high frequency oscillations originate as collective behaviour in populations of electrically coupled principal cell axonal compartments. Here we demonstrate that the superficial layers of medial entorhinal cortex can also generate high frequency oscillations associated with gamma rhythms. During persistent gamma frequency oscillations high frequency oscillations occur with a high bispectral coherence with the field gamma activity. Bursts of high frequency oscillations are temporally correlated with both the onset of compound excitatory postsynaptic potentials in fast-spiking interneurones and spikelet potentials in both pyramidal and stellate principal neurones. Both the gamma frequency and high frequency oscillations were attenuated by the gap junction blocker carbenoxolone. These data suggest that high frequency oscillations may represent the substrate for phasic drive to interneurones during persistent gamma oscillations in the medial entorhinal cortex.

Animals↗

PubMed2004

Low frequency corlico-muscular coherence during voluntary rapid movements of the wrist joint.

Rapid voluntary point-to-point wrist tracking movements are generated by the co-operative action of a large number of wrist muscles activated in a stereotypic pattern. This pattern is composed of a two burst sequence occurring in synergist and antagonist muscles. The time course and duration of these bursts are relatively fixed but the burst magnitude in any one muscle varies in relation to the direction of movement and the preferred directional tuning characteristic of the muscle. This creates a highly adaptive method for generating fast movements to different positions in space. In this study we have examined the extent to which this adaptive burst behaviour can be associated with activity changes occurring in the contralateral motor cortex. Time dependent coherence estimates were obtained from simultaneous recordings of the electroencephalogram (EEG) made from the contralateral sensorimotor cortex and the electromyogram (EMG) from various wrist flexor and extensor muscles during fast point-to-point wrist tracking movements. Using the onset of movement as a trigger, event related coherence estimates reveal the presence of short lasting periods of low frequency (<12 Hz) coherence during the execution of fast wrist movements. The onset and duration of the periods of low frequency coherence vary with direction of movement and the temporal burst profile of a particular muscle's EMG activity. It is therefore likely that a significant low frequency activation of the motor cortex plays a part in the generation of the EMG burst patterns that underpin rapid point-to-point movements of the human wrist.

Cerebral Cortex↗