Biomedical subjects

B R Parnas

Publications and source records attributed to B R Parnas.

4 recordsLinked to original sources

PubMed1996

Noise and neuronal populations conspire to encode simple waveforms reliably.

Sensory systems rely on populations of neurons to encode information transduced at the periphery into meaningful patterns of neuronal population activity. This transduction occurs in the presence of intrinsic neuronal noise. This is fortunate. The presence of noise allows more reliable encoding of the temporal structure present in the stimulus than would be possible in a noise-free environment. Simulations with a parallel model of signal processing at the auditory periphery have been used to explore the effects of noise and a neuronal population on the encoding of signal information. The results show that, for a given set of neuronal modeling parameters and stimulus amplitude, there is an optimal amount of noise for stimulus encoding with maximum fidelity.

Action Potentials↗

PubMed1994

Analysis of the response properties of a computationally efficient spike initiator model.

A simple model for neuronal spike initiation is presented. It comprises two linear differential equations and is based on the work of Hill, Rashevsky and Monnier (Rashevsky 1933; Monnier 1934; Hill 1936). Three different versions of the model and the corresponding assumptions are described. The intrinsic noise model used with the deterministic equations is described. The equations are analyzed through the direct solution of relevant equations and the technique of phase plane analysis. The analysis reveals that a subset of the model parameters is responsible for the distinction between spike initiator models which fire a single spike and those that fire repetitively in the presence of a sustained stimulus. Relationships between stimulus intensity and different modes of operation are derived. The effects of the three different versions of the model are compared analytically.

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PubMedDate not supplied

Simulation studies of vestibular macular afferent-discharge patterns using a new, quasi-3-D finite volume method.

A quasi-three-dimensional finite-volume numerical simulator was developed to study passive voltage spread in vestibular macular afferents. The method, borrowed from computational fluid dynamics, discretizes events transpiring in small volumes over time. The afferent simulated had three calyces with processes. The number of processes and synapses, and direction and timing of synapse activation, were varied. Simultaneous synapse activation resulted in shortest latency, while directional activation (proximal to distal and distal to proximal) yielded most regular discharges. Color-coded visualizations showed that the simulator discretized events and demonstrated that discharge produced a distal spread of voltage from the spike initiator into the ending. The simulations indicate that directional input, morphology, and timing of synapse activation can affect discharge properties, as must also distal spread of voltage from the spike initiator. The finite volume method has generality and can be applied to more complex neurons to explore discrete synaptic effects in four dimensions.

Action Potentials↗

PubMedDate not supplied

Theoretical bases of short-latency spike volleys in the peripheral vestibular system.

If a spike trigger zone exhibits the same sort of accommodation that has been found universally in peripheral axons and is an emergent property of the Hodgkin-Huxley model and other synthetic models of axonal membrane (1,2), then spike production will be favored by steep positive slopes of the waveform of the current into the trigger zone. Thus, large positive steps of axial current flowing nearly simultaneously into the trigger zones of many vestibular axons should produce a short-latency spike volley over those axons. Reasoning in terms of the small-signal (linear) transfer relationship for the cascade of components preceding the trigger zone, one can show that the ability to translate a stepwise change in head acceleration into a rapid increase in axial current into the trigger zone is more strongly dependent on the number of zeros at infinity from poles with long time constants (longer than those of the spike initiator) than it is on the values of the time constants themselves. Larger numbers of zeros at infinity make such translation increasingly difficult. Evidence from the work of Fernandez and Goldberg and others suggests (3-7) that the number is low. It may be lowest in jerk-sensitive units (8-9), in which case one would expect such units to make the greatest contributions to short-latency spike volleys.

Animals↗