Glutamatergic input from the insula to the ventral bed nucleus of the stria terminalis controls reward‐related behavior

Individuals suffering from substance use disorder often experience relapse events that are attributed to drug craving. Insular cortex (IC) function is implicated in processing drug-predictive cues and is thought to be a critical substrate for drug craving, but the downstream neural circuit effectors of the IC that mediate reward processing are poorly described. Here, we uncover the functional connectivity of an insular cortex projection to the ventral bed nucleus of the stria terminalis (vBNST), a portion of the extended amygdala that has been previously shown to modulate dopaminergic activity within the ventral tegmental area (VTA), and investigate the role of this pathway in reward-related behaviors. We utilized ex vivo slice electrophysiology and in vivo optogenetics to examine the functional connectivity of the IC-vBNST projection and bidirectionally control IC-vBNST terminals in various reward-related behavioral paradigms. We hypothesized that the IC recruits mesolimbic dopamine signaling by activating VTA-projecting, vBNST neurons. Using slice electrophysiology, we found that the IC sends a glutamatergic projection onto vBNST-VTA neurons. Photoactivation of IC-vBNST terminals was sufficient to reinforce behavior in a dopamine-dependent manner. Moreover, silencing the IC-vBNST projection was aversive and resulted in anxiety-like behavior without affecting food consumption. This work provides a potential mechanism by which the IC processes exteroceptive triggers that are predictive of reward

Salience processing and insular cortical function and dysfunction

The brain is constantly bombarded by stimuli, and the relative salience of these inputs determines which are more likely to capture attention. A brain system known as the 'salience network', with key nodes in the insular cortices, has a central role in the detection of behaviourally relevant stimuli and the coordination of neural resources. Emerging evidence suggests that atypical engagement of specific subdivisions of the insula within the salience network is a feature of many neuropsychiatric disorders