Short term depression unmasks the ghost frequency.

Tjeerd V Olde Scheper,Arjen Van Ooyen,Huibert D Mansvelder

doi:10.1371/journal.pone.0050189

Tjeerd V Olde Scheper, Arjen Van Ooyen + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0050189

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Journal: PloS one	Publication Date: Dec 5, 2012
Citations: 38	License type: CC BY 4.0

Affiliation: Oxford Brookes University, Vrije Universiteit Amsterdam

Abstract

Short Term Plasticity (STP) has been shown to exist extensively in synapses throughout the brain. Its function is more or less clear in the sense that it alters the probability of synaptic transmission at short time scales. However, it is still unclear what effect STP has on the dynamics of neural networks. We show, using a novel dynamic STP model, that Short Term Depression (STD) can affect the phase of frequency coded input such that small networks can perform temporal signal summation and determination with high accuracy. We show that this property of STD can readily solve the problem of the ghost frequency, the perceived pitch of a harmonic complex in absence of the base frequency. Additionally, we demonstrate that this property can explain dynamics in larger networks. By means of two models, one of chopper neurons in the Ventral Cochlear Nucleus and one of a cortical microcircuit with inhibitory Martinotti neurons, it is shown that the dynamics in these microcircuits can reliably be reproduced using STP. Our model of STP gives important insights into the potential roles of STP in self-regulation of cortical activity and long-range afferent input in neuronal microcircuits.

Highlights

The phenomenon of the missing fundamental frequency, often referred to as the Ghost Frequency, is the perceived pitch of a harmonic complex when the complex does not contain the pitch frequency itself
The method employed by the auditory system needs to be both accurate and generic in the sense that it does not rely on unique conditions, such as specific network structures or special dynamics
We extend this work using a dynamic synaptic activity model to show that Short Term Depression can effectively provide synchrony and frequency summation with high accuracy

Summary

Introduction

The phenomenon of the missing fundamental frequency, often referred to as the Ghost Frequency, is the perceived pitch of a harmonic complex when the complex does not contain the pitch frequency itself. A similar phenomenon has been observed in afferent motor input as a ghost motor response [1] It has not yet been shown how sensory systems perceive ghost frequencies, it has been conjectured that noise in sub-threshold activity is a mechanism to improve network performance and robustness [2]. Recent work indicates its existence in cortical microcircuits [10], the Calyx of Held [11], thalamo-cortical connections in V1 [12] and numerous other sites From these experimental results, it can be concluded that STP plays an important role in timing dependent processing throughout the brain in many different areas with different functionality. We show, using experimentally derived microcircuits, the likely function of STP within those circuits in self-regulation of cortical activity and long-range afferent input [10]

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