Vestibular neuromodulation: stimulating the neural crossroads of psychiatric illness

In a recent provocative Opinion article in Trends in Cognitive Sciences, Downar et al.1 (see also Goodkind et al.2) draw from quantitative metaanalyses of repositories of structural neuroimaging studies to propose a ‟common core” of brain regions whose function is disturbed in a wide variety of psychiatric disorders. Central to this core is the (dorsal) anterior cingulate cortex (ACC) and (anterior) insular cortex (IC). These regions map closely onto a functional anterior cinguloinsular network (aCIN), or ‟salience” network, that has also been identified with metaanalyses of thousands of neuroimaging studies. The psychiatric common core/aCIN is argued to stand at a crossroads position in the network architecture of the brain, being active during behavioural selfcontrol, emotion regulation, and social cognition, and acting as a switch to deploy other major functional networks mediating cognition and emotion. Dysfunction in this ‟hub” role can thus predispose to multiple psychiatric illnesses such as bipolar disorder, major depressive disorder, schizophrenia, obsessive compulsive disorder, anxiety disorders, post-traumatic stress disorder, attention deficit hyperactivity disorder, autism spectrum disorders, eating disorders and substance dependence disorders. Downar et al.1 also discuss prospects for precisely targeting key nodes of the common core for therapeutic effect, potentially with broadspectrum benefits across psychiatric disorders. They review various brain stimulation methods, such as electroconvulsive therapy (ECT), repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS), epidural cortical stimulation, and deep brain stimulation (DBS), and point out that the non-invasive techniques in particular require further development before being able to successfully target deeplysituated and relatively focal common core nodes like dorsal ACC and anterior IC, as well as relevant subcortical regions such as the putamen (PN) in the basal ganglia. It is suggested that targeting the common core/aCIN with brain stimulation could lead to improved treatments for many psychiatric illnesses, and in turn align psychiatry with neurology as psychiatric illness pathology becomes better defined.