Decades after the Vietnam war, a US army veteran recounts the intense flashbacks he still gets of the battlefield, triggered by something as innocuous as a thunderclap: “I am back in Vietnam. It is the middle of the monsoon. My hands are freezing and yet I am sweating... Suddenly I see my buddy Troy, his head on a platter, sent to our camp by Viet Cong,” he says in a well-documented case study.
Now, two city-based neuroscientists have decoded the anatomy of fear and show how sometimes this vital and primal response to danger can go completely awry, morphing into post-traumatic stress disorder (PTSD) seen often in soldiers and also in people who have been in near-fatal situations: sexual assault, natural disaster or accidents.
A study published in Nature Neuroscience, by Sumantra Chattarji and Supriya Ghosh, neuroscientists at National Centre for Biological Sciences, reveals how a certain set of neurons in the amygdala (the brain’s emotional hub), which once distinguished between safe and dangerous stimuli, begin responding even when there is no sign of threat.
For the experiment, the researchers trained rats to distinguish between two sound frequencies. One frequency was accompanied by a foot shock and the other was not. “When the shock was elevated, we found that one set of excitatory neurons that once responded only to the sound associated with a shock now began firing indiscriminately even to sound not accompanied by a shock,” said author Prof. Chattarji.
The scientists also found that a certain bio-chemical pathway — cAMP–PKA — was activated during this process of generalised fear. “This opens up neuronal and biochemical targets for therapies for PTSD, and this will be our next stage of research,” Prof. Chattarji said.
