Emotional Control Circuit Of Brain's Fear Response Discovered

Main Category: Neurology / Neuroscience
Also Included In: Biology / Biochemistry;  Psychology / Psychiatry
Article Date: 02 Oct 2006 - 0:00 PDT

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Colombia University Medical Center researchers have identified an emotional control circuit in the human brain which keeps emotionally intense stimuli from interfering with mental functioning. These results significantly enhance our understanding of the neurobiology underlying psychiatric disorders involving emotional control, such as post traumatic stress disorder (PTSD) or depression.

The research employed a novel test in which subjects were forced to detect and resolve attentional conflict created by emotionally powerful stimuli. Brain activity was monitored using functional magnetic resonance imaging (fMRI) that can detect moment-to-moment changes in neural activity. fMRI is a version of the widely-used clinical MRI scanning technique.

The study, which is published in the Sept 21, 2006 issue of Neuron, was led by a Columbia University Medical Center M.D./Ph.D. student, Amit Etkin, who explained that, "Tremendous knowledge exists about how our brains deal with cognitive distractions, but we know very little about how we deal with emotional distractions. This is something we constantly do in our everyday lives, otherwise we would be overwhelmed by every emotional trigger we encounter."

Dr. Etkin worked in the Columbia University Medical Center labs of Joy Hirsch, Ph.D., professor of neuroradiology and psychology, and director of the fMRI Research Center and Eric Kandel, M.D., Howard Hughes Medical Institute senior investigator, Fred Kavli Professor and Director of the Kavli Institute for Brain Sciences.

The current findings extend on a previous Neuron paper (Dec 16, 2004) in which Drs. Etkin, Kandel and Hirsch found that anxious individuals show more activity in the amygdala, a central brain region involved in the processing of negative emotions, when unconsciously perceiving fearful stimuli (please click here to read the Columbia press release:

http://cumc.columbia.edu/news/press_releases/hirsch_kandel_etkin_anxiety_neuron.html). When these stimuli were perceived consciously, however, the amygdalas of subject with both high and low levels of anxiety responded similarly.

Dr. Hirsch explained that this previous finding suggested that subjects were somehow able to control their conscious emotional responses, but that their unconscious responses may be more automatic. "Following the discovery of the amygdala's role in fear response, we decided to explore the finer points of the neurocircuitry of fear - how it is regulated and controlled in the brain," said Dr. Hirsch.

To study emotional regulation, Dr. Etkin collaborated with Tobias Egner, Ph.D., a post-doctoral fellow in Dr. Hirsch's lab, who has used fMRI to study non-emotional forms of attentional control. In the 2006 Neuron paper, subjects were asked to identify the facial expressions in photos shown to them as either happy or fearful. Across each face were the words FEAR or HAPPY, and were either congruent or conflicting from the facial expressions. When the word and face clashed, subjects experienced an emotional conflict, which slowed their performance and made them less accurate in identifying facial expressions.

Using a clever behavioral trick, however, the researchers were able to discriminate between brain circuitry that detected this emotional conflict from circuitry that resolved this conflict. They found that the amygdala generates the signal telling the brain that an emotional conflict is present; this conflict then interferes with the brains ability to perform the task. The rostral anterior cingulate cortex, a region of the frontal lobe, was activated to resolve the conflict. Critically, the rostral cingulate dampened activity in the amygdala, so that the emotional response did not overwhelm subjects' performance, thus achieving emotional control.

"This paper adds important regulatory circuit information about the fear response in the amygdala," said Dr. Hirsch. "For example, if someone is walking on an empty street at night and hears a loud banging sound in the near distance, the amygdala would immediately light up. But instead of always running in the opposite direction from the sound, the rostral cingulate determines if action is needed or not. For example, if it was a car door slamming, the rostral cingulate would shut down the amygdala."

"Based on these findings, tailored treatments may be developed in the future based on the biology of the person's disease," said Dr. Kandel. "For example, we may be able to tailor treatment for an individual depending upon whether anxiety is primarily manifested in the amygdala's response to unconscious threat, or primarily in the ability of the rostral cingulate to control conscious emotion."

"Interestingly, several studies have found that rostral cingulate activity predicts whether a depressed patient will respond to medication," said Dr. Etkin. "The findings from the current study, therefore, may help explain why more rostral cingulate activity may be beneficial."

The research team that worked on the 2006 Neuron paper also included Columbia University College of Physicians and Surgeons medical student, Daniel Peraza.

Columbia University Medical Center provides international leadership in pre-clinical and clinical research, in medical and health sciences education, and in patient care. The medical center trains future leaders and includes the dedicated work of many physicians, scientists, nurses, dentists, and public health professionals at the College of Physicians & Surgeons, the College of Dental Medicine, the School of Nursing, the Mailman School of Public Health, the biomedical departments of the Graduate School of Arts and Sciences, and allied research centers and institutions. http://www.cumc.columbia.edu.

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