Page 43 - Volume 12, Issue 2 - Spring 2012

AUDITORY CORTICAL FUNCTION:
INSIGHTS FROM CURRENT APPROACHES
Christoph E. Schreiner
Departments of Otolaryngology and Bioengineering University of California, San Francisco
San Francisco, California 94143
Patrick O. Kanold
Department of Biology University of Maryland College Park, Maryland 20742
Hisayuki Ojima
Department of Cognitive Neurobiology
Tokyo Medical and Dental University
1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8510, Japan
Shihab A. Shamma
Departments of Electric and Computer Engineering University of Maryland
College Park, Maryland 20742
Steven G. Lomber
Department of Physiology and Pharmacology Faculty of Medicine and Dentistry University of Western Ontario London, Ontario, Canada N6A 3K7
Over the last decade, an expand-
ing array of innovative
approaches has been used to
explore the organization, processing,
and behavioral/perceptual contribu-
tions of the auditory cortex in various
animal models. Several investigators
were invited to present an overview of
current developments in the field of
auditory cortical processing at the
occasion of Acoustics 2012 Hong Kong,
a joint meeting including the 163rd
meeting of the Acoustical Society of
America (ASA), the 8th meeting of the
Acoustical Society of China (ASC), the
11th Western Pacific Acoustics
Conference (WESPAC) and the Hong
Kong Institute of Acoustics (HKIOA).
In this article, a brief overview of five
different aspects of these influential
approaches represented at that meeting are presented to provide a mosaic of current progress in our understanding of auditory cortical function.
Synapses and receptive fields of the auditory cortex are plastic
A major feature of adult mammalian primary auditory cortex (AI) is frequency tuning. Frequency tuning is reflected in synaptic and spiking receptive fields, and it is loosely related to the fact that the relative strengths of exci-
tatory and inhibitory inputs are pro- portional across tone frequency; i.e., synaptic excitation and inhibition are essentially balanced in mature AI (Froemke et al., 2007; Tan and Wehr, 2009; Tan et al., 2004; Volkov and Galazjuk, 1991; Wehr and Zador, 2003; Zhang et al., 2003). Excitatory and inhibitory balance is interpreted in the sense that they are usually co-tuned, i.e., sharing best frequencies (BFs) and having correlated response magnitudes across other frequencies (Fig. 1A). However, although the relative ampli- tudes of inhibitory responses scale with the size of excitatory responses for a given stimulus, the onset of inhi- bition is delayed by a few milliseconds (Wehr and Zador, 2003; Zhang et al., 2003). As a consequence, there is a
42 Acoustics Today, April 2012
“Understanding how inputs
to cortical neurons are
coordinated is critical...since
changes in inputs ensure that
a neuron’s excitability and
functional feature selectivity
are appropriately configured
for both processing and
perceiving the sensory
environment.”
brief window in which excitatory responses can sum together and generate action potentials.
Though we have begun to understand the synaptic inputs to single neurons, it remains unclear how changes to specific inputs must be coordinated within larger neural net- works. Understanding how inputs are coordinated is critical, however, since changes in inputs ensure that a neuron’s excitability and functional feature selectivity are appropriate- ly configured for both processing and perceiving the sensory environment.