Article summary with Safety behaviours preserve threat beliefs: Protection from extinction of human fear conditioning by an avoidance response by Lovibond a.o. - 2009

There’s considerable evidence that access to within-situation safety behaviours can interfere with the beneficial effects of exposure therapy for anxiety. Similar outcome has been observed in panic disorder. The best explanation is the cognitive account which says that patients attribute the absence of the feared outcome to their safety behaviour and fail to update their threat beliefs. Exposure in the absence of safety behaviour is thought to disconfirm excessive threat beliefs and lead to long-term fear reduction.

A closely related phenomenon that’s been demonstrated in the conditioning laboratory is protection from extinction. In this procedure, a Pavlovian conditioned stimulus (CS) is established as a predictor of an unconditioned stimulus (US), and is then subjected to extinction by presenting the CS without the US. “Protection” refers to finding that extinction is impeded by the presentation of an inhibitory CS during the extinction phase. The best explanation for this effect is that the inhibitory stimulus cancels the expectancy of the US generated by the target excitatory stimulus, so that there’s no discrepancy between what’s expecting and what happens, no extinction.

The phenomenon of protection from extinction provides a potential lab model for investigating the role of safety information during exposure therapy. A study found that a conditioned inhibitor interfered with extinction of a target excitatory stimulus. But the primary sources of inhibition or safety in therapy are thought to be safety behaviours produced by patients themselves, as opposed to an external source.

This study uses a procedure recently developed to study instrumental avoidance learning. It builds on the Pavlovian fear conditioning procedure where different coloured shapes serve as CSs for shock or no shock. Sometimes participants have access to response buttons. Access is signaled by illumination of the buttons, but participants have to press the right button to avoid shock. Skin conductance and shock expectancy are recorded.

Method

Participants

65 undergraduate students, who volunteered.

Apparatus

Participants tested individually in a darkened room. CS’ were coloured squares and the US was an electric shock produced by a constant current generator.

Skin conductance was measured through electrodes attached to the second and third fingers of the participant’s non-preferred hand.

Procedure

Participants were told the experiment consisted of a number of trials with rest periods in between and that on each trial, a coloured square appeared for 5 seconds followed by a 10 second waiting period, followed by either a 0.5 second shock or no shock. They were told there was a relationship between the colour of the squares and the occurrence of the shock that they should try and work out. Participants were told that response buttons may light up, and that pressing a lit button may cancel a pending shock.  Participants were asked to use the expectancy pointer during the waiting period after the square disappeared to indicate their expectancy of whether a shock would occur or not.

Following this, the Pavlovian acquisition phase was designed to establish the CS-US contingencies prior to introducing opportunity for an avoidance response. Two CSs, A and C, were paired with electric shock (A+, B+), and a third CS presented without a shock (B-). No response buttons were illuminated during this phase.  In the Avoidance acquisition phase, participants were given the opportunity to make a button-press response during presentations of stimulus A. To simplify learning, only the correct response button was illuminated. If they pressed the button, the shock was cancelled.

In the Extinction phase, stimulus C was presented six times without shock. Protection group was given the chance to make the button-press response for this stimulus. The button was not illuminated for the control group. In the final (Test) phase, the impact of the extinction trials was examined by presenting C alone, without response opportunities.

Discussion

The experiment provided clear evidence for protection from extinction of a Pavlovian fear CS by an instrumental avoidance response. Control group showed normal extinction of stimulus C, whereas the Protection group, who made the avoidance response during the Extinction phase, showed little extinction. Adds to the evidence for protection from extinction in humans and extends it from external stimuli to an internal response.

Participants weren’t given a choice of responses, so the illumination of the correct response button was strongly correlated with the absence of the shock US. Was the critical factor in the protection effect light? No, the light was only correlated with the absence of the US as a result of performance of the instrumental button-press response.  

In general, the same pattern was observed in this experiment on both expectancy ratings and skin conductance. One point of divergence between the measures – when the avoidance response was made available in the Avoidance acquisition phase, it led to a modest reduction in shock expectancy ratings to stimulus A. Presumably due to prior instructions given that suggested pressing a response button may cancel shock. Opposite effect was observed on the skin conductance measure – making the avoidance response available led to an increase in skin conductance on the first A*(+) trial. This could be due to arousal associated with performing the avoidance response.

We interpret the protection from extinction effect as analogous to the role of within-situation safety behaviours in preserving threat beliefs and anxiety in patients undergoing exposure therapy. Shock expectancy ratings = threat beliefs, skin conductance = anxiety/fear. The results are consistent with the cognitive account proposed by Salkovskis et al. (1999). By this account, the Protection group attributed absence of the expected electric shock on C*= trials to the avoidance response. So when the response wasn’t available in the Test phase, they retained their high shock expectancy to C and showed strong anxiety. The Control group didn’t have an alternative explanation for the absence of the expected electric sock on C- trials, and were forced to revise their expectancy shock downwards – lowered their ratings and skin conductance responses in the Test phase.

It seems strange to account for conditioned responding in terms of a cognitive mechanisms as it’s been seen as a low-level, reflexive process. But recent evidence suggests that it may depend on high-level cognitive processes. This perspective is compatible with cognitive threat appraisal theories of anxiety. Expectancy of harmful outcomes may give a common explanatory mechanism cross fears derived from learning, observation, and instruction. Results imply that habituation of an innate fear response and extinction of an acquired fear response may both be based on a reduction in expectancy of threat.

Lastly, clinically, the present results support the strategy of minimizing safety behaviours during exposure therapy and giving participants clear cognitive rationale for doing so. The avoidance procedure provides a potential lab model to investigate the cognitive and other mechanisms underlying protection of beliefs against disconfirming evidence. This could be used to study potential positive benefits of safety manipulations, as well as interactions with other variables of therapeutic relevance like pharmacological agents.