Optical imaging of plastic changes induced by fear conditioning in the auditory cortex

Abstract

The plastic changes in the auditory cortex induced by a fear conditioning, through pairing a sound (CS) with an electric foot-shock (US), were investigated using an optical recording method with voltage sensitive dye, RH795. In order to investigate the effects of association learning, optical signals in the auditory cortex in response to CS (12 kHz pure tone) and non-CS (4, 8, 16 kHz pure tone) were recorded before and after normal and sham conditioning. As a result, the response area to CS enlarged only in the conditioning group after the conditioning. Additionally, the rise time constant of the auditory response to CS significantly decreased and the relative peak value and the decay time constant of the auditory response to CS significantly increased after the conditioning. This study introduces an optical approach to the investigation of fear conditioning, representational plasticity, and the cholinergic system. The findings are synthesized in a model of the synaptic mechanisms that underlie cortical plasticity.

Fear conditioning induces guinea pig auditory cortex activation by foot shock alone

“…Insofar as such maps are comprised of the preferential tuning of neurons across these fields, and frequency tuning is shifted during learning, it might be expected that the signal frequency would develop an expanded representation in the map during auditory fear conditioning. Such frequency-specific increase in representational area has been found in instrumental reward tasks involving training over months or weeks (Recanzone et al 1993;Rutkowski and Weinberger 2005;Hui et al 2009;Bieszczad and Weinberger 2010a, b;Ide et al 2012).…”

“…To investigate effects of conditioning on auditory cortex activity, we used a fear-conditioning paradigm in guinea pigs, pairing pure tones with foot shocks. Fear conditioning (Galván and Weinberger 2002;Ide et al 2012) and other behavioral and pharmacological paradigms (Ma and Suga 2005;Rutkowski and Weinberger 2005;Kacelnik et al 2006) have induced plasticity in various aspects of mammalian auditory cortical representations, but the possibility of signals in the absence of sound, elicited through auditory fear conditioning, remained unexplored. To measure auditory cortex activity, we employed the optical imaging technique (Horikawa et al 1996(Horikawa et al , 2001Hosokawa et al 2004;Ide et al 2012), which registers electrophysiological activity of neuron populations at millisecond precision, by recording fluorescent signals from the cortical surface after the application of a voltage-sensitive dye.…”