How two brain areas interact to trigger divergent emotional behaviors

New research from the University of North Carolina School of Medicine for the first time explains exactly how two brain regions interact to promote emotionally motivated behaviors associated with anxiety and reward.

The findings could lead to new mental health therapies for disorders such as addiction, anxiety, and depression. A report of the research was published online by the journal, Nature, on March 20, 2013.

Located deep in the brain’s temporal lobe are tightly packed clusters of brain cells in the almond shaped amygdala that are important for processing memory and emotion. When animals or people are in stressful situations, neurons in an extended portion of the amygdala called the bed nucleus of the stria terminalis, or BNST, become hyperactive.

But, almost paradoxically, neurons in the BNST, which modulate fear and anxiety, reach into a portion of the midbrain that’s involved in behavioral responses to reward, the ventral tegmental area, or VTA.

“For many years it’s been known that dopamine neurons in the VTA are involved in reward processing and motivation. For example, they’re activated during exposure to drugs of abuse and naturally rewarding experiences,” says study senior author Garret Stuber, PhD, assistant professor in the departments of Psychiatry and Cell Biology and Physiology, and the UNC Neuroscience Center.  “On the one hand, you have this area of the brain – the BNST – that’s associated with aversion and anxiety, but it’s in direct communication with a brain reward center. We wanted to figure out exactly how these two brain regions interact to promote different types of behavioral responses related to anxiety and reward.”

In the past, researchers have tried to get a glimpse into the inner workings of the brain using electrical stimulation or drugs, but those techniques couldn’t quickly and specifically change only one type of cell or one type of connection. But optogenetics, a technique that emerged about seven years ago, can.

In the technique, scientists transfer light-sensitive proteins called “opsins” – derived from algae or bacteria that need light to grow – into the mammalian brain cells they wish to study. Then they shine laser beams onto the genetically manipulated brain cells, either exciting or blocking their activity with millisecond precision.