Major depressive disorder and bipolar I are both debilitating mood disorders, categorized by persistent depressive symptoms. The depressive symptoms of both conditions are thought to perhaps share underlying brain pathways, and could very well be more closely linked than was originally thought. If this were indeed the case, people who suffer from these conditions would appear to have the same areas of their brain activated under depressed conditions. Any differences seen in brain activation could than be attributed to underlying differences for each condition. Identifying and coming to better understand these underlying differences could result in better treatment options, as well as an overall better understanding of how both conditions work (Cerullo et al. 2014).
To date it is believed that people who are suffering from bipolar I disorder show impairment in the part of the brain that is responsible for regulating emotion, this is known as the cortico-limbic region (Cerullo et al. 2014). The deficits are most clearly seen in the amygdala (the part of the brain responsible for controlling a wide range of emotions, most commonly fear (Dubuc, 2002)), the anterior cingulate gyrus (which plays a roll in processing and modulating of emotional expression as well as emotional learning and vocalization of ones emotions (Joseph, 2000)), the ventrolateral prefrontal cortex (which is used to assess and characterize the different features of environmental stimuli (Moss, 2009)) (Cerullo et al. 2014). Patients who suffer from major depressive disorder show an emphasized level of abnormality within the hippocampus (the area of your brain where emotion is transferred into memory (Phelps, 2014)) and the dorsolateral prefrontal cortex (this structure works in conjunction with the ventrolateral prefrontal cortex but, instead of assessing the world around you, this area of the brain is used to determine appropriate responses to the assessed stimuli (Moss, 2009)) (Cerullo et al. 2014).
To test this, Michael A Cerullo et al. took participants who have been diagnosed with these disorders and put them in an fMRI. An fMRI is essentially a large x-ray machine, that allows the brain to be imaged, however the fMRI not only shows the structure of the brain but it can also detect activity levels within the brain, causing the different structures to light up in an index of colors based on the level of activity. To test the varying levels of brain activity participants in the study were scanned while partaking in something known as a modified continuous performance task with emotional and neural distracters. This is just a fancy way of saying the following: the participants underwent scans of their brains while partaking in an activity in which visual cues flashed across the screen. These cues consisted of simple colored squares and simple coloured circles. The participant had to press a button whenever a circle flashed onto a screen and refrain from responding whenever a square was on the screen. In order to make the brain light up areas that correspond to emotional processing the flashing images were infused with images that have been proven to either elicit an emotionally negative response or an emotionally neutral response. This would allow the researchers to see if an emotional response alters a person perception and accuracy while at the same time looking at which portions of the brain are being highlighted and used (Cerullo et al.2014)
The results of the study showed that the major differences between patients with bipolar I disorder and major depressive disorder when viewing emotional stimuli can be pinpointed to the primary and secondary visual processing regions of the brain, with people suffering from bipolar I having a lower level of activation in these areas when compared to the major depressive patients and the control group. During the emotional component of the task there were found to be activation differences in the regions of the brain that are involved in emotional processing, self-referential imagery and processing of emotional facial expressions. These differences were not however linked to the cortico limbic region of the brain as was originally thought. This means that there could be a similar underlying mechanism for the depressive nature seen in major depressive disorder as well as bipolar I (Cerullo et al. 2014)
Work Cited:
Cerullo, M.A., Eliassen, J.C., Smith, C.T., Fleck, D.E., Nelson, E.B., Strawn, J.R., Lamy, M., DelBello M.P., Adler
C.M., Strakowski, S.M. (2014). Bipolar I disorder and major depressive disorder show similar brain activation
during depression [Internet] Bipolar Disorders 16: 703-712.
Websites used for definition of structures:
Dubuc, B. (2002). The amygdala and its allies. Retrieved Feb. 12, (2015) from
http://thebrain.mcgill.ca/flash/d/d_04/d_04_cr/d_04_cr_peu/d_04_cr_peu.html
Joseph, R. (2000). Cingulate Gyrus. Retrieved Feb. 12, (2015) from http://brainmind.com/Cingulate.html
Moss, S. (2009). Ventrolateral Prefrontal Cortex. Retriebed Feb 12, (2015) from
http://www.psych-it.com.au/Psychlopedia/article.asp?id=313
Phelps, J.R. (2014). Memory, Learning, and Emotion: the Hippocampus. Retrieved Feb. 12, (2015) from