Taming the Amygdala in PTSD

Fear is an adaptive emotion that helps us cope with threatening situations. Deep within the temporal lobe of the brain is the amygdala, the most studied brain area involved in fear. The amygdala uses all kinds of information from outside and inside the body to help us interpret and react to danger.

The Amygdala and Fear

Upon detecting a threat, the amygdala causes reactions that prepare us to deal with danger. For example, if you hear a sudden noise behind you when walking alone at night, you might experience a racing heart, changes in breathing, and tension in your muscles. These amygdala-dependent reactions enhance the body's readiness to respond to the threat.

The amygdala is also important for making fearful memories. When an individual encounters a threatening situation, the amygdala forms a memory of that event, tying together all the parts of the environment, such as sounds, smells, and visual features. These fearful memories help us adapt and make faster decisions in the future. However, in some people who have experienced trauma, the amygdala is hyperactive, which is believed to cause maladaptive behavior that is distressing. An example of this is the symptoms associated with post-traumatic stress disorder (PTSD).

Amygdala Activity Rhythms Associated With Threats

Distinct types of brain rhythms are associated with various cognitive functions, including fear memory. In the amygdala, a type of rhythm called theta is thought to help the amygdala process information and form memories. Most of what we understand about amygdala theta rhythms comes from animal studies because measuring it requires placing electrodes into the brain. Theta has been recorded in the amygdala of patients with epilepsy undergoing neurosurgery; however, whether theta might be different in PTSD patients is poorly understood. Finding out how theta functions in people suffering from PTSD could be critical for developing new treatments.

Recording Theta in the Human Amygdala

In a remarkable study, Gill et al. recorded amygdala rhythmic activity as part of voluntary clinical trials for PTSD. Patients were implanted with electrodes into the amygdala, and brain activity was recorded for more than one year. Activity in the amygdala was recorded while patients looked at unpleasant images and listened to audio recordings of their own trauma-related memories. Patients also self-reported their symptoms using a questionnaire, and the researchers were able to link amygdala theta activity changes to times when PSTD symptoms were at their worst.

Neuromodulation of Amygdala Theta for Treatment of PTSD

The authors then applied an innovative technique known as closed-loop stimulation to change amygdala function in the hope of reducing PTSD symptoms. In closed-loop stimulation, the surgical device was used to stimulate electrically the amygdala when theta was detected. Remarkably, using this treatment strategy for one year led to significantly reduced severity of PTSD symptoms as well as reduced amygdala theta activity during aversive stimuli.

Future Directions

Admittedly, this is an invasive approach that requires neurosurgery and careful monitoring of patient health. Other clinical trials in PTSD patients are underway that are using non-invasive neurofeedback with functional MRI to downregulate amygdala function during trauma recollection. While this neurofeedback technique is showing promise for giving patients control over amygdala activity, it has yet to reduce symptoms significantly when compared to control subjects. Nonetheless, further work using these types of approaches is called for and necessary to help the millions of individuals suffering from PTSD.