The habenula is a conserved epithalamic nucleus and a key component of the Dorsal Diencephalic Conduction System (DDCS), a pathway known to modulate brainstem monoamine transmitter release influencing mood, behaviour, aversion, and reward suppression. Often termed the ‘disappointment circuit’, the DDCS transduces complex emotional and reward information from the limbic forebrain into changes in serotonin, dopamine and noradrenaline release. These neurotransmitters are thought to be involved in psychiatric conditions such as depression, psychosis and anxiety, and many pharmacological therapies such as antidepressants (increasing available serotonin and noradrenaline) and antipsychotics (dopamine receptor blockade), target these neurotransmitters directly. As a key modulator of monoaminergic function, the habenula could be a valuable potential therapeutic target for the treatment of depression, psychosis and anxiety. Indeed, there have been some pilot studies showing lasting improvement in symptoms of depression following deep brain stimulation (DBS) of the habenula. (Germann, 2021)
The proposed project aims to measure habenular volume using MRIcron in previously scanned depressed patients and controls. Evidence to date has been widely unreliable with no standard means or protocol for volumetric analysis in determining its ambiguous borders, as well as a wide range of reported volumetric values. This will be achieved using a combination of two views, coronal and axial, to more accurately depict its borders. As a secondary goal, this study hopes to compare the volumes of left and right sides in hopes of serving as a means of accurately pinpointing a target for deep brain stimulation. It is hoped that an increased total volume would be seen in depressed subjects which would reflect the increased involvement of the habenula in negative reward processing.