Synaptic Mechanisms of Direction Selectivity in Primary Auditory Cortex

Abstract

Frequency modulation (FM) is a prominent feature in animal vocalization and human speech. Although many neurons in the auditory cortex are known to be selective for FM direction, the synaptic mechanisms underlying this selectivity are not well understood. Previous studies of both visual and auditory neurons have suggested two general mechanisms for direction selectivity: (1) differential delays of excitatory inputs across the spatial/spectral receptive field and (2) spatial/spectral offset between excitatory and inhibitory inputs. In this study, we have examined the contributions of both mechanisms to FM direction selectivity in rat primary auditory cortex. The excitatory and inhibitory synaptic inputs to each cortical neuron were measured by in vivo whole-cell recording. The spectrotemporal receptive field of each type of inputs was mapped with random tone pips and compared with direction selectivity of the neuron measured with FM stimuli. We found that both the differential delay of the excitatory input and the spectral offset between excitation and inhibition are positively correlated with direction selectivity of the neuron. Thus, both synaptic mechanisms are likely to contribute to FM direction selectivity in the auditory cortex. Finally, direction selectivity measured from the spiking output is significantly stronger than that based on the subthreshold membrane potentials, indicating that the selectivity is further sharpened by the spike generation mechanism.

Learning a novel phonological contrast depends on interactions between individual differences and training paradigm design

“…On the other hand, the present study focused on low-level domain-specific factors that constrained learning achievement, allowing us to better specify the mechanistic bases of individual variability in learning this phonological contrast. We identified pitch contour perception as the major predictor of learning achievement in our task; the biological mechanisms of this ability are increasingly well understood (Bendor and Wang, 2006;Ye et al, 2010;Loui et al, 2009;Plack et al, 2005), including also its genetic (Drayna et al, 2001) and environmental influences (Pantev et al, 1998;Wong et al, 2007b). By understanding the underlying biological sources of variability that result in differences in learning, we will be in a better position to design instructional programs that address those differences and maximize each individual's learning potential.…”

Auditory System

“…However, there are exceptions to this rule (Wu et al, 2006(Wu et al, , 20082011Zhou et al, 2010;Ye et al, 2010) so that the tunings of excitation and inhibition do not match perfectly. For the frequency tuning, inhibition is broader than excitation within the frequency range that generates spike responses.…”

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“…Additionally, development of FM direction selectivity in the rat ACx is influenced by exposure to FM sweeps (Insanally et al, 2009). An added advantage of studying FM processing is that the underlying circuit and cellular mechanisms have, in part, been worked out (Ye et al, 2010; Pollak et al, 2011; Fuzessary et al, 2011).…”