Depression is a relatively common psychiatric condition that is on the rise in America today. Depression can vary greatly in its severity and forms of debilitation from person to person, making it difficult to coordinate effective treatments to relieve its symptoms. Currently, it is well established that individuals with depression experience an overall decrease in their brain activity, but the reasons behind this are unknown. Research has suggested that symptoms of depression may be the result of abnormalities and miscommunication in the brain, specifically between structures in the limbic system and the frontal cortex. Limbic system structures are thought to be involved in mood regulation and memory whereas the frontal cortex region of the brain is associated with higher level thinking and complex cognitive processes. Disruptions in the communication between these regions may result in distorted ways of thinking and inaccurate perceptions of the world. This understanding of low brain activity and possible misfires in the brain gives rise to the use of transcranial magnetic stimulation, or TMS, as a way to stimulate and reorganize the brain to relieve depressive symptoms.
An article in the Scientific American describes a way in which TMS is targeted to stimulate regions of the brain, therefore allowing it to rewire itself for optimal connectivity. An electromagnetic coil is placed on the scalp at a specific location to stimulate the left frontal cortex, a region of the brain known to have especially decreased activity in those with depression. Stimulation of this area allows for the activation of that brain region while simultaneously providing an access point through which the magnetic stimulation can rewire deeper subcortical regions. Because this form of treatment has offered relief for many individuals with depression, it offers support in favor of the theory that depression may be the result of miscommunication and ‘faulty wiring’ of the brain. While the use of TMS provides a basis for further research into the neurological causes of depression, it also leaves many unanswered questions. Specialists are still unsure of the exact mechanisms in the brain TMS operates by to reduce depressive symptoms. Understanding these mechanics would allow for more personalized treatment and could provide insight as to why individuals with depression experience such a wide range of symptoms.
Dr. Melissa Hebscher has conducted research using TMS to investigate the ways in which the brain can regulate and communicate with itself to coordinate specific neurological functions. Dr. Hebscher’s study on theta-gamma phase amplitude coupling, specifically, sheds light on how the brain coordinates activity via neural oscillations in across different regions of the brain. It does this by coupling the phases of neural oscillations, or brain waves, to create a communication and modulation system. Although Dr. Hebscher’s work focuses on the use of TMS to uncover the ways in which our episodic autobiographical memory operates, this technique may offer an opportunity to dissect how frontal cortical regions communicate with subcortical regions in the production of depressive symptoms. Dr. Hebscher explains that magnetoencephalogram signals, or MEG, can measure neural activity after repetitive TMS has manipulated the oscillations in the medial temporal lobe, called theta waves, to modulate gamma waves in the precuneus. Although she found that dysregulation of this neural communication resulted in deficits in autobiographical memory recall, Dr. Hebscher also referenced how the increase in magnitude of these oscillations using TMS can result in improvements in memory recall. This seems to be mildly similar to how TMS may work to improve symptoms of depression as it increases the activity in the brain.
These discoveries may make one curious if similar TMS and MEG signal techniques can be utilized to identify similar phase coupling between brain regions, specially the frontal cortex and various regions of the limbic system. This could therefore allow for the discovery of disruptions in neural activity for those with depression and how TMS can recoordinate that activity to allow for healthy, functional communication in the brain. If conclusive evidence is found regarding the types of neural oscillations involved in creating depressive symptoms, the use of TMS could evolve to target and localize treatments for depression.
Additionally, Dr. Hebscher’s research describes the involvement of the precuneus in recalling memories in the first person. It was noted that the greater the regulation of the gamma waves in the precuneus, the better the autobiographical memory recall. The extent to which theta waves regulate gamma waves is dependent on the amplitude of these neural oscillations. Because individuals with depression have decreased activity in the precuneus, it may be possible that the neurons synchronously firing are not creating a strong enough oscillation to allow for efficient first-person memory recall. This may explain why individuals with depression tend to experience deficits in memory and feelings of dissociation. If TMS can be used to stimulate the neural activity in the left frontal cortex, perhaps individuals with depression experiencing these specific symptoms can receive TMS treatment that specifically targets the precuneus similarly to how Dr. Hebscher’s study describes.
Dr. Hebscher’s Research:
Hebscher, Melissa & Levine, Brian & Gilboa, Asaf. (2017). The precuneus and hippocampus contribute to individual differences in the unfolding of spatial representations during episodic autobiographical memory. Neuropsychologia. 110. 10.1016/j.neuropsychologia.2017.03.029.
Hebscher, Melissa & A Meltzer, Jed & Gilboa, Asaf. (2019). A causal role for the precuneus in network-wide theta and gamma oscillatory activity during complex memory retrieval. eLife. 8. 10.7554/eLife.43114.
TMS Article:
Zarei, K. “Fighting Depression with Magnets”. Scientific American. 20 Dec. 2017 https://blogs.scientificamerican.com/observations/fighting-depression-with-magnets/
No comments:
Post a Comment