Friday, February 29, 2008

Brain systems mediating aversive conditioning

Buchel, C., Morris, J., Dolan, R.J., & Friston, K.J. (May 1998). Brain systems mediating aversive conditioning: an event-related fMRI study. Neuron, Vol. 20, 947-957.

Classical conditioning refers to a type of associative learning whereby a previously neutral stimulus (CS) comes to elicit a behavioral response by being paired with an aversive unconditioned stimulus (US). This study implemented a human classical conditioning paradigm in which images of faces (CS) were paired with an aversive tone (US). To assess which areas of the brain were related to conditioning, event-related fMRI responses were compared between presentation of conditioned stimuli (CS+) and unconditioned stimuli (CS-) after skin conductance indicated the conditioning regimen was completed successfully. To be more accurate, CS- was compared to the occasional trials of CS+ which were not followed by a tone.

Unequivocal differential responses were found in two cortical areas: the anterior cingulate cortex (ACC) and the anterior insula. These structures receive input from the amygdala, which also shows interesting activation patterns during this paradigm. The lateral amygdala in particular shows time-dependent neural responses, with higher than baseline responses at first but habituating over time. A possible explanation is a negative feedback loop, an analgesia kicked off by the amygdala and mediated by endogenous opioids which leads to reduced conditioning over time. Finally, differential activation was also witnessed in the red nucleus together with premotor structures, characteristic of response expression.

Happy 50th post!!! And happy bissextile day!!!

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