Thursday, December 22, 2011

TMS (Boyden MIT): The Open Noninvasive Brain Stimulator

The goal of this project ( is to design a simple, safe, effective TMS device for modulation of emotion, sleep, attention, and other central nervous system properties.
Many commercial entities sell TMS hardware and software, often for prices exceeding $50,000. We will devise a TMS device that will be constructable by a practitioner skilled in electrical engineering, for less than $400.

The project comprises at least the following 8 components. The logical way to begin is to A) figure out the field geometry desired at the specific depth under the skull, B) design a prototype coil, preferably with standardized values, C) pick the capacitor and resistor adjoining, D) work your way back to the power supply.

1. a reinforced coil (e.g., of copper wire) geometrically appropriate for stimulating the brain (e.g., a figure-8 coil, containing two circular loops, between 3 and 7 cm in diameter),

1b. a testing tank which would hold saline, to mimic the volume conductor of the brain, and thereby permit the electric field to be mapped for various coils and pulse protocols,

2. the control circuitry for charging up a high-capacity capacitor or bank of capacitors, via a power supply system connected to an AC wall source or battery source, and then controlling the discharge of the capacitor into the coil,

3. mechanical hardware for holding and positioning the coil with respect to the head,

4. safety circuitry that limits the current discharged and the repetition rate of the stimulator,

5. an optional measurement device (e.g., fluxgate magnetometer) to measure the magnetic field induced, and

6. computer software and interface hardware for connecting a computer to the control circuitry, and for displaying hardware status and/or error events.

7. integration with EEG or IR was brought up by many attendees of the session at Foo Camp. The contributors decided this should be built in, a priori.

8. OTHER THOUGHT: transcranial direct current stimulation (tDCS) has, like TMS, been shown to improve working memory and mood. Shall we design our TMS device with the capability of doing simultaneous tDCS? It could complicate things somewhat. Hoewver, the methodology is dead simple — apply a DC current across two electrodes, attached to the scalp!

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