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.

Keywords: Auditory cortex; Fear conditioning; Optical imaging; Plastic change; Voltage sensitive dye.

Fig. 1

Normal conditioning and sham conditioning protocol

Fig. 2

A schematic view of the optical recording system

Fig. 3

Tonotopic map in the auditory cortex of guinea pig

Fig. 4

a Auditory responses to CS (12 kHz) and non-CS (4, 8, 16 kHz) recorded before and after the normal conditioning. b Auditory responses to CS (12 kHz) and non-CS (4, 8, 16 kHz) recorded before and after the sham conditioning

Fig. 5

a Area ratio of each group at the sound frequency of 4–16 kHz. b Comparison of area ratio between normal, sham, non-CS and CS groups. (Error bar is SEM. Normal: n = 5, Sham: n = 5, * P < 0.05; ** P < 0.01, NS no significant differences)

Fig. 6

Comparison of ΔRR in the three groups of normal/sham conditioning and naïve. ΔRR is change of R–R interval during 10 s after CS onset. (Error bar is SEM. Naïve: n = 6, Normal: n = 5, Sham: n = 5, * P < 0.05, NS no significant differences)

Fig. 7

Time course of normalized ΔF/F at 4–16 kHz a before and b after normal conditioning. Time course of normalized ΔF/F at 4–16 kHz c before and d after sham conditioning

Fig. 8

a Peak value of normalized ΔF/F at 4–12 kHz before and after normal conditioning. b Peak value of normalized ΔF/F at 4–12 kHz before and after sham conditioning. (Error bar is SEM. Normal: n = 5, Sham: n = 5, * P < 0.05)

Fig. 9

a Rise time constant of optical response at 4–16 kHz before and after normal conditioning. b Rise time constant of optical response at 4–16 kHz before and after sham conditioning. (Error bar is SEM. Normal: n = 5, Sham: n = 5, * P < 0.05)

Fig. 10

a Decay time constant of optical response at 4–16 kHz before and after normal conditioning. b Decay time constant of optical response at 4–16 kHz before and after sham conditioning. (Error bar is SEM. Normal: n = 5, Sham: n = 5, * P < 0.05)