Scientists Identify Brain Circuit That Drives Pleasure-Inducing Behavior

Amygdala is that part of our brain which balances memory, emotional reactions and decision making processes and is responsible for making us stressed when we have that really important, or not so important, exam coming up. At least this is the train of thought scientists followed till the last 22nd March.

Graduate students Joshua Kim and Xiangyu Zhang authored a paper on an experiment supervised by Susumu Tonegawa, the Picower Professor of Biology and Neuroscience and a director at the RIKEN-MIT Center; which sheds new light on the activities of amygdala and show that they are hugely responsible to generate the happy feelings you get while biting on the piece of dark chocolate.

The experiment

The past body of research had been dedicated to unravel the circuitry of the brain from where negative behavior seemed to stem. Tonegawa and his team of neuroscientists from MIT conducted a groundbreaking research which has succeeded in confirming that amygdala consists of both reward and fear circuitry and is intricately involved in generating positive emotions.

Amygdala changed from the fear center of the brain to the reward generator in the experiment carried out by Tonegawa’s team on mice.Infact this research is a continuation of last year’s work where neurons from Basolateral Amygdala were thought to relay positive and negative information to nucleus of central amygdala.

Initially the central amygdala neurons were mapped into seven groups depending on the kind of genetic expression they point to. Then the mapped regions were exposed to optogenetics which basically uses light to control neural activity. What emerged from the experiment was five regions out of seven imitate reward related behavior which drove the mice to expose themselves more to light source. One region was found to be associated with fear related behavior.

Though about 90% of discovered amygdala tissue has been found to contribute to positive behavior, about 10% is still undiscovered and unmapped and according to Tonegawa the neural circuitry in the uncharted regions may be responsible to trigger negative emotions.

Generally, an amygdala can be said to exhibit appetitive behavior catering to satisfy the specific drive at an instant.

Aftermath of the experiment

The basolateral amygdala is being studied for the role it plays in fear extinction, which basically is a process used to overwrite the existing sets of fearful memories and replace it with positive ones and is used to treat cases of depression, post-traumatic stress disorder etc. Since the misconceptions about central amygdala acting as seat of negative stimuli has been invalidated, a new region called periaqueductal gray has emerged as research favorite to locate the pain and fear related stimuli.

The success of the experiment lies in firmly establishing the amygdala as a seat of positive stimuli and refuting its image as the fear center.Scientific community is elated at the new unexpected set of discovery. Scientists not officially related to the experiment have been quoted to find the new information to herald exciting times for brain research.