Navigating through life requires balancing emotion & reason, a feat accomplished by the brain region “area 32” of the anterior cingulate cortex. Area maintains emotional equilibrium by relaying information between cognitive and emotional brain regions, consistent with new research in monkeys published in JNeurosci.
Emotional balance goes haywire in mood disorders like depression, resulting in unchecked negative emotions and an inability to break out of rumination. In fact, people with depression often have an overactive area 25, a area involved in emotional expression.
Healthy emotional regulation requires communication between cognitive regions, just like dorsolateral prefrontal cortex (DLPFC), and emotion regions, like area 25, also referred to as the subgenual cortex. But because these 2 areas are weakly connected, there must be a middleman involved.
Superficial layer neurons from the DLPFC send feedforward projections to deep layers of A32. A32 sends projections to A25 originating in superficial and deep layers of A32. By predominantly targeting disinhibitory neurons in superficial layers, pathways from A32 to the superficial layers of A25 may allow excitatory signals to propagate through the local circuitry. By predominantly targeting PV neurons in deep layers, A32 engages a stronger inhibitory system and certain features a stronger ability to dampen activity in local circuitry.
Source : Joyce et al
Joyce et al. used bidirectional neuron tracers to see the connections between the DLPFC, area 25, and area 32, a possible middleman, in rhesus monkeys. The DLPFC connects to the deepest layers of area 32, where the strongest inhibitory neurons reside. Area 32 connects to each layer of area 25, positioning it as a strong regulator of area 25 activity.
In healthy brains, the DLPFC signals to area 32 to balance area 25 activity, allowing emotional equilibrium. But in depression, silence from the DLPFC leads to an excessive amount of area 25 activity and out-of-control emotional processing.
