Our thoughts are built on electricity.
More accurately, brain cells known as neurons communicate with each other using electrical signals. When these signals are faulty, neurological disorders, including depression, schizophrenia and Parkinson disease, can arise.
Faulty signaling can manifest in a variety of ways: there can be excessive electrical signaling in and across brain regions (too much excitatory activity) or important signals can be wrongly blocked (too much inhibitory activity). To treat unbalanced activity, which can occur in conditions such as depression, an innovative therapy known as repetitive transcranial magnetic stimulation (rTMS) has been shown to help. The therapy does not require surgery: instead, electrical currents are applied to a patient’s scalp, which help to restore balance in defective brain circuits.
During rTMS, patients receive a series of electrical impulses that are separated by rest intervals, called inter-trial intervals (ITIs). Changing the frequency of electrical impulses or the duration of ITIs can alter how brain circuits respond to rTMS treatment. However, the optimal ITI to elicit therapeutic effects remains unknown.
Krembil Senior Scientist Dr. Robert Chen recently investigated how changing the ITI influenced brain activity: specifically, the balance between increased (excitatory) or reduced (inhibitory) activity. He found that rTMS has a greater influence on inhibitory brain circuity when the ITI duration was lessened; the proportion of patients whose inhibitory brain circuitry responded to rTMS went from 43 to 73% when ITI was reduced from 32 to 4 seconds. He also found that these inhibitory circuit changes occurred independently of excitatory circuit changes.
“This is the first study to demonstrate that it may be possible to substantially reduce treatment duration without affecting rTMS efficacy,” says Dr. Chen. “If we can reduce the ITI, then we can deliver rTMS treatment in shorter sessions, reducing patient inconvenience and associated health care costs.”
This work was supported by the Canadian Institutes of Health Research, Brain Canada, the National Institutes of Health, the Klarman Family Foundation, the Edgestone Foundation, the Ontario Brain Institute, and the Toronto General & Western Hospital Foundation.
Cash RF, Dar A, Hui J, De Ruiter L, Baarbé J, Fetters P, Peters S, Fitzgerald PB, Downar J, Chen R. Influence of inter-train interval on the plastic effects of rTMS. Brain Stimul. 2017 Mar 2. doi: 10.1016/j.brs.2017.02.012.