How does the brain balance emotion and reason?

Neuroscientists uncover a middleman between cognitive and emotional brain regions

By Molly Gluck

(Image source: Mary Kate Joyce and Helen Barbas, Boston University Neural Systems Laboratory and Jess Holz, MFA)

What would life be like if we could only act on emotion? On the flip side, what would happen if no one felt emotion — and we were only guided by reason? Envisioning both scenarios highlights the critical importance of balancing emotion and reason.

Healthy emotional regulation requires communication between cognitive brain regions, like the dorsolateral prefrontal cortex (DLPFC), and emotional brain regions, such as area 25. However, these two areas are weakly connected — and until now, it has been unknown how they interact. Boston University neuroscientists Drs. Helen Barbas, Mary Kate Joyce, Yohan John and and Miguel Ángel García-Cabezas (now at University of Madrid) uncovered a middleman responsible for maintaining emotional equilibrium: area 32.

The researchers identified area 32 using neural tracers to visualize the connections between cognitive (DLPFC) and emotional (area 25) brain regions in rhesus monkeys. Their discovery helps us better understand what makes certain people more susceptible to depression — and can inform different treatment approaches.

In healthy brains, the DLPFC signals area 32 to balance area 25 activity, enabling emotional stability. Emotional balance goes haywire in mood disorders like depression, leading to unchecked negative emotions and an inability to break out of rumination. This runaway negative emotion is often caused by an overactive area 25. The researchers speculate that in individuals where area 32 has weaker connections with DLPFC and area 25, emotional regulation may be more difficult — perhaps rendering individuals vulnerable to depression. Furthermore, identifying and evaluating the strength of area 32’s connections with DLPFC and area 25 can help inform which treatment approach to take for people suffering from depression — ranging from cognitive behavior therapy, to medication, to deep brain stimulation.

So, what do these critical interactions between brain regions actually look like? The researchers take us into their lab for an inside-look:

Connections from area 32 (green) transfer information to local inhibitory neurons (blue, red) in area 25, a process that may contribute to emotional regulation. (Image source: Mary Kate Joyce and Helen Barbas, Boston University Neural Systems Laboratory)

Zooming in to look at circuitry in the brain can reveal patterns that are important for our everyday life. On the left, connections from area 32 (green) commingle with local inhibitory neurons (blue, red) in area 25. Higher resolution microscopy techniques (middle, right) allow us to determine if area 32 has a preference for interacting with specific types of inhibitory neurons. ­­These interactions may be critical for emotional regulation. (Image source: Mary Kate Joyce and Helen Barbas, Boston University Neural Systems Laboratory)

This image highlights the types of inhibitory neurons in area 25 — a brain area that is important for emotions and is disrupted in depression. Area 25 has less of the powerful red inhibitory neurons, which may leave the area vulnerable to runaway activity seen in depression. (Image source: Mary Kate Joyce and Helen Barbas, Boston University Neural Systems Laboratory)

Connections from area 32 make close contact with red parvalbumin inhibitory neurons in area 25. This pattern of interaction may allow for the dampening of local emotional signaling in area 25, and contribute to emotional regulation processes. (Image source: Mary Kate Joyce and Helen Barbas, Boston University Neural Systems Laboratory)

This 3D reconstruction created from high resolution microscopy depicts dense interactions between area 32 (blue) and neuronal elements in area 25 (green, excitatory dendrites; orange, inhibitory dendrite; pink, inhibitory cell body). These interactions may be crucial for emotional regulation, and disruption of them may impact resilience or vulnerability to depression. (Image source: Mary Kate Joyce and Helen Barbas, Boston University Neural Systems Laboratory and Jess Holz, MFA)

For more information, access the full research paper, published in the Journal of Neuroscience here.

For additional commentary by Boston University experts, follow us on Twitter at @BUexperts. Follow the Boston University Center for Systems Neuroscience at @buCSNneuro, the Boston University College of Health & Rehabilitation Sciences: Sargent College at @BUSargent, and the Boston University School of Medicine at @BUMedicine on Twitter. Follow Dr. Yohan John on Twitter at @DrYohanJohn.