The discovery has been made by Massachusetts Institute of Technology neuroscientists. The research shows that a circuit in the central amygdala structure of the brain responds to rewarding events (as well as fearful ones). The amygdala is one of two almond-shaped groups of nuclei located deep within the temporal lobes of the brain. It performs a primary role in the processing of memory, decision-making, and emotional reactions (the amygdalae are considered part of the limbic system).
The connection between the central amygdala and reward has been tested out using mice. In the study, the researchers activated the circuit of interest with certain stimuli. This led to the rodents seek these stimuli further. The researchers also tested out the circuit that controls responses to fearful events.
Talking with Bioscience Technology, lead researcher Susumu Tonegawa explains how the discovery was somewhat of a surprise and runs against previously accepted thinking in neuroscience: “It’s surprising that positive-behavior-promoting subsets are so abundant, which is contrary to what many people in the field have been thinking.”
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The research shows there are two distinct populations of neurons in a different part of the amygdala. This region is known as the basolateral amygdala. It appears these two populations are genetically programmed to encode either fearful or happy memories. Thus fear and happiness are, from the neurological perspective, intertwined.
To better understand the functions of the central amygdala cells that receive information from the basolateral amygdala the researchers analyzed the genetic profiles of the central amygdala neurons. From this they divided the neurons into seven groups, according to different genetic markers and their anatomical location. By controlling neuron activity with light (a method called optogenetics) the researchers were able to investigate the functions of each population. This led to the discovery that five of these populations stimulate reward-related behavior. Using the mice it was found that when the mice were exposed to light they repeatedly sought out more light exposure since the neurons were driving the reward circuit.
The inference from the study is that rewriting fearful memories so that they are associated with more positive feelings could be undertaken if the appropriate neurons are activated. This could help to address problems of anxiety and depression.
The findings are published in the journal Neuron. The research paper is titled “Basolateral to Central Amygdala Neural Circuits for Appetitive Behaviors.”
