AX+, BX- Discrimination Learning in the Fear-Potentiated Startle Paradigm: Possible Relevance to Inhibitory Fear Learning in Extinction

Abstract

The neural mechanisms of fear suppression most commonly are studied through the use of extinction, a behavioral procedure in which a feared stimulus (i.e., one previously paired with shock) is nonreinforced repeatedly, leading to a reduction or elimination of the fear response. Although extinction is perhaps the most convenient index of fear inhibition, a great deal of behavioral work suggests that postextinction training conditioned stimuli are both excitatory and inhibitory, making it difficult to determine whether a neural manipulation affects inhibition, excitation, or some combination thereof. For this reason we sought to develop a behavioral procedure that would render a stimulus primarily inhibitory while at the same time avoiding some of the issues raised by the traditional conditioned inhibition paradigm, namely second-order conditioning, external inhibition, and configural learning. Using the fear-potentiated startle paradigm, we adapted an AX+, BX− training procedure in which stimuli A and X were presented simultaneously and paired with shock, and stimuli B and X were presented simultaneously in the absence of shock. In testing, high levels of fear-potentiated startle were seen in the presence of A and AX and much lower levels were seen in the presence of B and AB, as would be predicted if stimulus B were a conditioned inhibitor. We believe this method is a viable alternative to the traditional conditioned inhibition training procedure and will be useful for studying the neural mechanisms of fear inhibition.

Inhibition of fear is differentially associated with cycling estrogen levels in women

“…The fear inhibition test stimulus was a compound of the previously conditioned A and B cues to determine transfer of inhibition (by B) to the fear response to A. 30 The A, B and X stimuli were green, purple or blue light panels 5 cm × 10 cm in size (counterbalanced colour assignment across participants) mounted on the wall 1 m from the participant's seat. The aversive US was a 250 ms airblast with an intensity of 140 psi directed to the larynx.…”

Estrogen Disrupts the Inhibition of Fear in Female Rats, Possibly through the Antagonistic Effects of Estrogen Receptor α (ERα) and ERβ

“…The training protocol was modified from that of Myers and Davis (2004) Training. Beginning 24 h after the pretest, rats were returned to the startle chambers and 5 min later presented with the first of 10 noise bursts, which served to habituate the startle response to a stable baseline.…”

“…On AXϩ trials, animals are presented with A and X in a simultaneous compound that coterminates with footshock, and on BXϪ trials animals are presented with B and X in a simultaneous compound that is not followed by footshock. Discrimination between AX and BX is indicated by an increase in acoustic startle amplitude [fearpotentiated startle (FPS)] in the presence of AX and, as training progresses, little to no fear-potentiated startle in the presence of BX (Myers and Davis, 2004). As a function of this training, A accrues excitatory value and elicits fear, whereas B becomes inhibitory (Wagner et al, 1968).…”

Optimizing Exposure Therapy for Anxiety Disorders: An Inhibitory Learning and Inhibitory Regulation Approach

“…Direct evidence of deficits in inhibitory control is dependent on laboratory paradigms capable of teasing apart inhibition from excitation during fear learning, such as 'conditional discrimination' [ Myers and Davis, 2004;Jovanovic et al, 2005]. Using this paradigm, evidence for impaired inhibitory mechanisms has been established for PTSD [Jovanovic et al, 2009], and highly traumatized samples [Jovanovic et al, 2010].…”