Amygdala lesions block conditioned enhancement of the early component of the rat eyeblink reflex.

Abstract

A tone conditioned stimulus (CS) previously paired with a grid shock unconditioned stimulus (US) can greatly enhance the early electromyographic (EMG) component (R1) of the rat eyeblink reflex. The hypothesis that the central nucleus of the amygdala (ACe) is an essential part of the circuitry mediating conditioned R1 enhancement was tested. After bilateral ACe lesions (L) or a sham operation (S), rats received paired presentations of the CS and US (P) or explicitly unpaired CS and US presentations (U), resulting in 4 groups: P/S, P/L, U/S, and U/L. ACe lesions completely prevented conditioned R1 enhancement, which was only exhibited in Group P/S. In the latter group, the "preextinction" conditioned enhancement effect was roughly a 2-fold increase in the R1 magnitude. Circuit-level mechanisms are discussed, and some advantages of the eyeblink EMG response in this general conditioning paradigm are considered.

Perirhinal Cortex Supports Delay Fear Conditioning to Rat Ultrasonic Social Signals

“…When identically measured, the intensity of the 22 kHz tone was 67 dB. As in our previous studies (Choi et al, 2001;Lindquist and Brown, 2004), the intensity of the 4 kHz tone was 75 dB, measured using the C scale of a digital sound meter (model 33-2055;range, 32-10,000 Hz;Realistic, Fort Worth, TX).…”

“…The coterminating, grid-shock US (500 msec, 1.0 mA) was produced by a small-animal shock generator (E13-14; Coulbourn Instruments, Allentown, PA). The root mean square current was measured conventionally (Choi et al, 2001) from the voltage across the smaller of two resistors (1 and 100 k⍀) connected in series between adjacent grid bars. The conditioning chambers each had a standard grid floor consisting of parallel steel rods (5 mm diameter and 15 mm spacing).…”

“…The interior dimensions were 22 (length) ϫ 28 (width) ϫ 42 (height) centimeters. The chambers were housed in sound-attenuating cubicles (Choi et al, 2001;Lindquist and Brown, 2004). Cue testing was done in a context that differed in three respects: the chamber was cleaned with a different odorant; the standard grid floor was replaced with a solid one; and a light bulb (ϳ25 lux) at the side of the chamber was illuminated.…”

Central amygdala lesions inhibit pontine nuclei acoustic reactivity and retard delay eyeblink conditioning acquisition in adult rats

“…(e) UR peak amplitude (mean ± SE) during CS-US trials was significantly reduced, on Session 1 only, in lesion rats relative to sham controls (asterisk) Eyeblink UR peak amplitudes were also analyzed in sham and lesion rats based on US-alone and CS-US paired trials. The former reflects UR strength while the latter measures associative UR facilitation due to the fear-enhancing effects of the tone CS following its pairing with the aversive US (Brown, Kalish, & Farber, 1951;Choi, Lindquist, & Brown, 2001). Results for US-alone trials, based on 2 (Lesion) × 4 (session) repeated measures ANOVAs, uncovered a significant main effect for Session only, F(3, 42) = 3.32, p < .05, signifying CEA lesions had no deleterious effect on processing or responding to the US signal (see Fig.…”

Learning not to Fear: Neural Correlates of Learned Safety

“…When contrasting learned safety and learned fear, several important insights about the neurobiology of learned safety can also be drawn from a host of studies in which explicitly unpaired 'control' groups had been studied. Important examples include the assessment of generalization described above (Bang et al, 2008;Ito et al, 2009;Laxmi et al, 2003), the effect on sleep (Jha et al, 2005;Madan et al, 2008), and investigations on the role of the amygdala (Choi et al, 2001;Maren, 2000;Maren et al, 2001). …”