33-year-old Xiao Wang, an engineer working in the Hsinchu Science Park, developed symptoms of anxiety, insomnia, and brain fog after contracting COVID-19. Initially, he underwent repetitive transcranial magnetic stimulation (rTMS) therapy at an external clinic, with stimulation targeting the left prefrontal cortex of the brain. However, after 10 sessions, his panic, anxiety, and insomnia worsened. Seeking further help, he consulted Dr. Zhou Bohan, a psychiatrist at China Medical University Hsinchu Hospital. During the examination, Dr. Zhou discovered that Xiao Wang was left-handed. Using functional near-infrared spectroscopy (fNIRS), a brain imaging technique, it was revealed that the patient's "dominant brain" was located in the right hemisphere, contrary to the typical left-hemisphere dominance in right-handed individuals. Consequently, Dr. Zhou administered reverse stimulation to the right prefrontal cortex. After 20 treatment sessions, Xiao Wang's panic and anxiety gradually improved.
According to neuroimaging studies, the left prefrontal cortex of depressed individuals tends to exhibit decreased functionality. Therefore, traditional rTMS therapy for depression typically involves stimulating the left prefrontal cortex to achieve symptom improvement. However, previous brain imaging studies have often excluded left-handed participants to avoid confounding results. As a result, it remains unclear whether left-handed individuals with depression exhibit "left-sided hypoactivity" in the prefrontal cortex. Consequently, when treating left-handed patients clinically, the standard approach still involves stimulating the left hemisphere, as with right-handed patients.
Past brain imaging research has shown that 94% of right-handed dominant brains are left-hemisphere dominant, whereas only 78% of left-handed dominant brains exhibit left-hemisphere dominance. Therefore, left-handed individuals with depression undergoing brain stimulation therapy have a higher chance of receiving rTMS treatment on the "wrong side," leading to counterproductive outcomes. Left-handed individuals make up approximately 15% of the general population. In Taiwan's cultural context, there has been a tendency to forcefully convert naturally left-handed individuals to right-handed, resulting in many right-handed depressed patients potentially being latent left-handed individuals. Therefore, extra attention is needed in their treatment.
It is recommended to assess handedness before TMS treatment, which can be done through tools like the Edinburgh Handedness Inventory. However, the most accurate and direct approach would be to use brain imaging techniques such as functional near-infrared spectroscopy (fNIRS) to observe the location of the dominant brain hemisphere directly. This helps avoid misplacement during treatment and ensures optimal efficacy of TMS therapy.
