Channels for Learning Fear
The amygdala is a region of the brain that regulates human emotions, including emotions learned by experiences, whether positive from a reward or negative from a punishment. The exact mechanisms by which this learning occurs, however, are not well understood. One insight that has been gained is that dopamine, a neurochemical released in the amygdala during learning, is thought to be the key player in learning about both aversive and appetitive stimuli. The neurochemical regulates many types of amygdala neurons in distinct manners, and delineating the role of each neuron in learning to fear or to embrace is a long, complicated process.
In this study, the researchers sought to tease out the dopamine effect on one specific type of neuron, parvalbumin-containing cells, which are known to rapidly inhibit other neurons and promote brain oscillations. More specifically, they investigated the role of dopamine in changing communication between the parvalbumin cells and the neighboring excitatory or inhibitory neurons within the basolateral amygdala.
By using a technique known as optogenetics, the researchers activated parvalbumin cells using flashes of light and measured responses from neighboring neurons. The experiments performed in the brain slice from a mouse revealed that dopamine, by acting on the specific receptor D2, prevented parvalbumin cells from inhibiting excitatory neurons but did not interfere with suppression of inhibitory neurons. The findings explain how dopamine reduces overall inhibition within the basolateral amygdala and promotes neuronal activity, which is likely the mechanism facilitating formation of new emotional memories.
This study adds understanding to the molecular processes involved in associating life experiences with positive or negative outcomes—such as rewards and punishments—leading to the formation of long-term emotional memories. With enough knowledge of the cellular and molecular processes underlying emotional learning, particularly fear learning, it may be possible to develop novel treatments for stress and trauma-related psychological conditions, such as post-traumatic stress disorder.
Genetically introducing proteins called channelrhodopsins into neurons allows scientists to activate them with a simple flash of light. The ability to directly control neural pathways is an emerging technique that promises to be a powerful tool for untangling the chaotic web that is the human brain.
It remains a puzzle which molecules inside neurons enable the selectivity of dopamine effects. Why does dopamine suppress some synapses, but not others? Why is selectivity observed in parvalbumin cells, but not all neurons? Identifying molecular targets responsible for the cell and synaptic selectivity of dopamine in the amygdala is the next step toward revealing new means for moderating learned emotional responses.
Where to Find It:
Chu HY, Ito W, Li J, Morozov A. Target-specific suppression of GABA release from parvalbumin interneurons in the basolateral amygdala by dopamine. J Neuroscience, 2012; 32(42):14815–20.