Terminating Fear Conditioning
There are two ways of reducing fear conditioning physiological arousal, extinction and thought suppression. Extinction is the reexperiencing of the conditioned stimulus (CS) in absence of the unconditioned stimulus (US) until the conditioned response (CR) arousal disappears, when the CS is no longer associated with the US. Thought suppression is the retrieval inhibition of cognition during the course of memory formation. Anderson and colleagues (2004) have found that thought suppression during and immediately after a task disrupts short-intermediate term memory formation and the future ability for remembering peripheral (and fine) task or event related details. It also involves activations of the midcingulate (MCC) and dorsolateral prefrontal (dlPFC) cortices (Wyland et al., 2003). These researchers also found that thought suppression was negatively correlated with hippocampal retrieval processes.
Thought suppression can be differentiated from emotional suppression, which activates slightly different regions. According to Ohira and colleagues (2006) suppressing emotion enhances physiological arousal evidenced in increased skin conductance response (SCR). Enhanced SCR during the suppression state is associated with medial orbitofrontal cortex (mOFC) activation. It also activates the lateral prefrontal cortex (-30,52,-2) with, according to this study’s authors, sagittal activations extending medially. Again suppressing the retrieval of emotion was negatively associated with entorhinal-hippocampal activity (26,-6,-22). Attending to emotion during an emotionally enhancing task activates both the amygdala and sensory regions of the anterior temporal pole. When findings for thought and emotion suppression during short-intermediate term memory formation are combined, thought suppression is associated with cognitive retrieval deficits (with activations in the dlPFC and MCC and deactivations in the hippocampus) and emotional suppression with sustained (SCR) arousal (with activations in the mOFC and deactivations in the anterior hippocampus). This may have relevance for understanding PTSD.
References
Anderson, M.C., Ochsner, K.N., et al., (2004). Neural systems underlying the suppression of unwanted memories. Science, 303(5655), 232-235.
Ohira, H., Nomura, M., et al., (2006). Association of neural and physiological responses during voluntary emotion suppression. Neuroimage, 29(3), 721-33.
Wyland, C.L., Kelley, W.M., et al., (2003). Neural correlates of thought suppression. Neuropsychologia, 41(14), 1863-7.