‘White noise, sugar and mixed signals
The researchers used an animal model of extinction in which rats were trained to associate a short burst of white noise with a sugary liquid. Once the rats had learned that the white noise predicted sugar, extinction training was implemented in which the noise was presented over and over again without sugar.
The researchers noted that rats eventually learned to stop responding. But when the rats were again given a small drop of sugar followed by presentations of the noise, they quickly went back to reacting as though it once again signalled the availability of sugar.
So, using optogenetics, the researchers selectively activated the infralimbic cortex during presentations of the noise after the rats received a drop of sugar.
This technique allowed them to amplify the activity of neurons in the infralimbic cortex during cue presentations — potentially the same neurons that store the memory that the white noise cue no longer predicts sugar.
Chaudhri's research team discovered that activating the infralimbic cortex reduced the return of responding to the cue that had been triggered by the drop of sugar. It was as though they had reactivated the memory acquired during extinction, that the white noise no longer signaled sugar.
‘It’s about having control over actions and reactions’
“For us, making this discovery is quite significant,” Chaudhri says. “It suggests that this particular part of the cortex is a critical player in our ability to inhibit responses to cues that predict desirable things, like sugar, an area of research that has been underexplored until now.
“This research paves the way for future work to identify new pharmaceutical treatments that could amplify the ability of infralimbic neurons to inhibit responding to cues. It’s about having control over actions and reactions.”
Extinction is a fundamental psychological process that happens in many different organisms, ranging from worms to mice to rats to humans. Chaudhri explains that her team’s discovery-driven research has helped to advance scientific knowledge of this critical process, while also having implications for human disorders like drug addiction.
“Cues associated with drug abuse can precipitate relapse in individuals recovering from drug addiction. Recovery is most effective in those individuals who are able to inhibit their reactions to cues that are associated with drugs,” she says.
She also notes that this research may apply to people suffering from post-traumatic stress disorder, who would gain from being able to stop responding to triggers of their trauma.
This work was made possible, in part, by the Facilities Optimization Program supported by Concordia’s Office of the Vice-President, Research and Graduate Studies, the Federal Research Support Fund, and grants from the Natural Sciences and Engineering Research Council and the Canada Foundation for Innovation.
Read the published study: Optogenetic Activation of the Infralimbic Cortex Suppresses the Return of Appetitive Pavlovian-Conditioned Responding Following Extinction.
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