A 2006 study done by Malek Bajbouj et al published in Biological Psychiatry has revealed some interesting results regarding differences in cortical inhibition in patients exhibiting unipolar depression compared to healthy controls. Much prior research has been done on the subject of neurotransmitters such as GABA (gamma-aminobutyric acid) that play a role in the pathophysiology of depression. GABA is a known mechanism of cortical inhibition (the overall activity of the brain and the process by which chemical transmitters regulate brain function), and several previous studies have established that in depressed subjects GABA levels are unusually low. This can have several implications for the process of communication in the brain. Bajbouj et al use transcranial magnetic stimulation (TMS) to directly measure the effects that low GABA levels have on cortical inhibition, in this case specifically in the motor cortex. Areas of the motor cortex known for controlling hand movement were stimulated by TMS and the subsequent muscle action potential was recorded by EMG. Depressive patients were shown to have lower motor thresholds and shorter silent periods (periods of inactivity between potentials) than those of the healthy controls. This is an interesting finding in that it suggests a correlation between depression and motor control and function. I think that it is particularly interesting in the way that it manages to build on previous studies and knowledge regarding the function of GABA in cortical inhibition. While previous research provided a sort of background theory regarding the role of GABA, TMS allowed the researchers to directly measure the implications of decreased neurotransmitters on cortical inhibition. This shows the importance of using a multi-faceted approach in research. The study also exhibits the way that brain function is a distributive process, in that motor control was affected by as seemingly unrelated a thing as depression.
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