TMS uses an alternating current passed through a metal coil placed against the scalp to generate rapidly alternating magnetic fields.
This passes through the skull nearly unimpeded and induce electric currents that depolarise neurons in a focal area of the surface cortex
The magnetic field generated by TMS is comparable to that of a standard magnetic resonance imaging (MRI) device (approximately 1.5 to 3 Tesla); however, the TMS field is very focal (beneath the coil).
What Part of The Brain Does TMS Target?
Transcranial Magnetic Stimulation (TMS) primarily targets the Dorsolateral Prefrontal Cortex (DLPFC) of the brain. The DLPFC is involved in managing executive functions such as decision-making, problem-solving, and controlling attention and behavior. TMS stimulates regions of the brain that are underactive in patients with depression, anxiety disorder and chronic pain. By stimulating this region, TMS aims to normalise brain activity, contributing to the alleviation of symptoms associated with these conditions.
During TMS treatment, magnetic s fields timulate neural activity in the underactive areas. When this is done tens of thousands of times over a course of 4–6 weeks, lasting changes in brain circuity occur.
The exact mechanisms of action for TMS is unknown. One hypothesis is that stimulation of discrete cortical regions alters pathologic activity within a network of grey matter brain regions that are involved in mood regulation and connected to the targeted cortical sites. To find out more, please visit About TMS.
Both ECT and TMS have been shown to increased monoamine activity (seritonin in particular) and assist in the normalisation of the Hypothalamic pituitary axis.
The effect of TMS varies based on a number of factors. These include whether a high frequency of magnetic stimulation is used. When this occurs, the targeted neurons are stimulated. We generally used high frequency stimulation when target the left prefrontal cortex in the treatment for Depression.
In contrast, low frequency stimulation appears to inhibit cortical activity (and is usually directed at the right prefrontal cortex). Inhibitory stimulation to the Right DLFPC is an alternative treatment used in depression. This can be useful in patients who are at a high risk of seizure (Eg. Depending on their medication). Inhibitory stimulations greatly reduce any risk of seizure.
In a systematic review by Noda et al, the review examined 66 studies in depressed patients who were treated with TMS targeting the dorsal lateral prefrontal cortex and found that high frequency TMS generally increased regional cerebral blood flow and that low frequency TMS generally decreased regional cerebral blood flow
The intensity of the treatment is the other main parameter we can change to ensure efficacy.
If you would like to know how your GP or psychiatrist could refer you for TMS, please visit our TMS Referrals page.
If you are a psychiatrist or pain specialist looking to introduce TMS into your clinic, please visit our Partnering With Us page