Biomedical subjects

P R Churchward

Publications and source records attributed to P R Churchward.

3 recordsLinked to original sources

PubMed1997

A comparison of methods used to detect changes in neuronal discharge patterns.

The discharge pattern of two thalamic neurones was recorded from a conscious monkey performing voluntary movements about the wrist joint. The neuronal discharge was displayed as a raster centred on movement of the wrist. The discharge patterns of both neurones was very strongly correlated with movement. Three experienced researchers were asked to examine the data and to classify every part of each trial as background discharge, 'on' (increased firing rate) or 'off' (decreased or zero firing rate) and to mark the times that neuronal discharge changed state. A 'standard output' was made from these classifications. A back-propagation artificial Neural Network (the Network) was used to model the standard output and cumulative sums (CUSUMs) and maximum likelihood was then performed on the data and compared with the Network. There was a high correlation between the output of each observer (r > 0.61) and the standard output and between the Network and the standard output (r > 0.99). However the correlation between standard output and CUSUMs (r = 0.06) and standard output and maximum likelihood (r = 0.36) was much lower. The Network could be trained with as few as 12 trials, indicating a high degree of constancy in the methods employed by the observers. The Network was also highly efficient at detecting changes in state of neuronal activity (r > 0.99). In summary, when used on single trial data, visual inspection is a reliable method for detecting timing of change neuronal discharge and is superior to CUSUM and maximum likelihood. As well it is capable of detecting neuronal discharge state: that is whether firing rate is increased, normal or decreased. Neural Networks promise to be a useful method of confirming the consistency of visual inspection as a means of detecting changes in neuronal discharge pattern.

Action Potentials↗

PubMed1996

The relationship between monkey ventrolateral thalamic nucleus activity and kinematic parameters of wrist movement.

Extracellular recordings were made from single neurones in the cerebellar thalamus (75 neurones) and the VPLc (44 neurones) of four conscious moving monkeys. The experiment was designed to establish the discharge of ventrolateral thalamic neurones encodes information about kinematic parameters. The animals were trained to resist unexpected perturbations of the wrist and to perform skilled, voluntary wrist movements, producing stereotyped reflex and active movements with a wide range of durations and amplitudes. Statistical analysis of the discharge pattern associated with individual trials of movement was performed. In various maintained wrist positions there was a significant correlation (P < 0.05) between frequency of tonic discharge and joint position in 40% of the cerebellar thalamic neurones and in 54% of VPLc neurones. The phasic neuronal discharge associated with stereotyped movement often appeared "velocity-or acceleration-like'. However, statistical analyses revealed that the phasic discharge of only a small percentage of cerebellar thalamic and VPLc neurones was correlated with duration of movement, peak velocity or acceleration. The percentage of cerebellar thalamic neurones with discharge correlated to kinematic parameters was much greater when an unexpected change in the gain between joint angle and screen display led to errors in tracking the target. It is concluded that the cerebello-thalamo-cortical (CTC) pathway, carries information regarding maintained joint position but not velocity or acceleration of movement during a stereotyped task. However, the CTC pathway has a greater capacity to signal information about movement velocity and acceleration when there is a mismatch between the intended and actual movement.

Animals↗

PubMed1992

A frequency analysis of neuronal activity in monkey thalamus, motor cortex and electromyograms in wrist oscillations.

1. Extracellular recordings were made in three monkeys while recording from neurones in the motor cortex (eighty-four cells), ventro-posterior lateralis pars caudalis (VPLc, forty-two cells) and cerebellar thalamus (seventy-seven cells). 2. This experiment was designed to produce active and reflex movements of varying velocities in order to study the relationship between amplitude of velocity and magnitude of neuronal discharge of thalamic neurones. The active movements were voluntary rapid alternating movements (RAMs) of the wrist and the reflex movements were produced by forcibly oscillating the wrist joint between frequencies of 1 and 7 Hz (forced oscillations). 3. This study was also designed to examine cerebellar influences on a reflex path, namely the transcortical reflex loop. Forced oscillations were predicted to provide circumstances where active damping was required to prevent excessive oscillations in the reflex path. Rapid alternating movements of the wrist were predicted to provide circumstances where oscillations at the natural frequency in that reflex path would support and propagate the movements. 4. Forced oscillations from 1 to 7 Hz produced movements of different velocities. VPLc and cerebellar thalamic neurones discharged in relation to the duration of movement in a particular direction, but their discharge levels were unrelated to the magnitude of the velocity. Motor cortex neurones fired in a pattern which was related to the timing but not the magnitude of the acceleration. 5. In forced oscillations of the wrist the resonant frequency was between 3 and 7 Hz. They may be controlled in part by a transcortical reflex. The cerebellar thalamic neurones did not fire before motor cortex neurones. Therefore, it is unlikely that the cerebello-thalamo-cortical pathway is necessary to damp these potentially unstable oscillations by an effect on antagonist-related cortical neurones. 6. Rapid alternating movements (RAMs) of monkeys' wrists were performed in a stereotyped fashion over a narrow range of frequencies with the greatest displacement in joint angle and peak velocity at the natural frequency of 3-5 Hz. 7. During the performance of RAMs, neuronal discharge modulated sinusoidally in the VPLc, cerebellar thalamus and motor cortex. There was no relationship between velocity and neuronal discharge of the cerebellar thalamic and motor cortical neurones but there did appear to be a relationship between velocity and VPLc neuronal discharge. 8. The onset of electromyogram (EMG) discharge changed earlier than neuronal discharge in the motor cortex and thalamus during the performance of RAMs.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗