Human Brain Relies on Old and New Mechanisms for Diminishing Fear

A new study suggests that although humans may have developed complex thought processes that can help to regulate their emotions, these processes are linked with evolutionarily older mechanisms that are common across species. The new research provides new insights into the way the brain manages fear, and may help in the search for novel pharmacologic and therapeutic treatments for anxiety disorders.

"The ability to eliminate, control, or diminish negative emotional responses is important for adaptive function and critical in the treatment of psychopathology,” said study author, Dr. Mauricio Delgado, from Rutgers University (New Brunswick, NJ, USA). "Recent research examining the neural mechanisms for diminishing fears has focused on two techniques: [fear] extinction, which has been explored across species, and cognitive emotion regulation strategies, which are unique to humans.” Earlier research in rodents and humans has implicated activity in the amygdala and ventral medial prefrontal cortex (vmPFC) in extinction. In contrast, neural circuits underlying cognitive strategies to regulate emotions are not as well understood.

Dr. Delgado, Dr. Elizabeth A. Phelps, from New York University (NYU; New York, NY, USA), and their colleagues were interested in examining the similarities and differences of diminishing fear through both techniques. They used similar experimental paradigms with different means of controlling fear to directly compare the neural mechanisms that mediate extinction and emotional regulation. A typical fear conditioning method was combined with a measurement of physiologic arousal to examine extinction, while a cognitive emotion regulation strategy was also implemented. Functional magnetic resonance imaging (fMRI) scanning was utilized to compare the neural activation patterns of extinction and emotional regulation.

The researchers noted that the lateral prefrontal cortex regions engaged by cognitive emotion regulation strategies influenced the amygdala and diminished fear through similar vmPFC connections that are thought to suppress the amygdala during extinction. Taken together, the findings indicate that there is overlap in the neural circuitry of diminishing learned fears through emotion regulation and extinction and that vmPFC may play a general regulatory role in diminishing fear across a range of paradigms.

"Our results suggest that even though humans may have developed unique capabilities for using complex cognitive strategies to control emotion, these strategies may influence the amygdala through phylogenetically shared mechanisms of extinction," explained Dr. Phelps. "Extinction and cognitive emotion regulation may be, in part, complementary in that they rely on a common neural circuitry and, perhaps, similar neurophysiological and neurochemical mechanisms.”

The study was published in the September 11, 2008, issue of the journal Neuron.

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