Title

Neural modeling of the cochlear nucleus

Date of Completion

January 1992

Keywords

Health Sciences, Audiology|Biology, Neuroscience|Computer Science

Degree

Ph.D.

Abstract

Computational models which take into account both linear and nonlinear membrane properties were developed for stellate, bushy, and fusiform cells of the mammalian cochlear nucleus. These single cell models are based on a simplified R-C electrical circuit for the soma, similar to Hodgkin-Huxley formulations. In order to allow these models to reproduce the nonlinear behaviors in the bushy and fusiform cells, as observed from previous in vitro intracellular studies, an additional 'lumped' conductance branch was added. Action potential generation was adapted from previous work of MacGregor. These 'soma' models reproduce the unique current-voltage (I-V) and spike discharge properties of CN cell types and show the potential for modeling many other neurons.^ In addition, a unique method for modeling electrotonic dendritic processing was developed which allows rapid computation of spatiotemporal dendritic processing in passive, homogeneous, dendritic cables The method is based on the convolution of the dendritic impulse response function with a synaptic conductance representation, yielding a family of curves representing the current at the soma as a result of synaptic events located at various electrotonic distances from the soma. The results of simulations with this method are similar to those obtained using more computationally intensive compartmental dendrite models. In addition, this new approach allows more traditional neural network studies the ability to incorporate more realistic properties in their individual nodes without sacrificing computational speed.^ The soma models, with the above dendrite models added on to them, were used in simulations involving large numbers of modeled neurons. Simulations included step current inputs, simulated auditory nerve (AN) input representing a 5 kHz pure tone stimulus, and interneuronal connectivities. Post-stimulus time histogram (PSTH) subclasses, including Chop-S, Chop-T, O$\sb{\rm c}$, primarylike, pauser, and build-up types were reproduced using both step current and AN inputs. A current-shunting hypothesis is proposed to explain the delay behavior of fusiform cells. Excitatory-inhibitory response area (EIRA) subclasses of CN neurons were also reproduced and found to require particular anatomical constraints on the circuitry. ^