
Credit: Dicemanic, via Flikr
There has been an extended buzz in the news media about the use of transcranial “stimulation” techniques to enhance or impair math learning. Popular methods involve the application of a magnetic field or an electrical current to the surface of the skull, which can selectively disrupt (inhibit) or excite cells near the cortical surface.
Transcranial stimulation techniques

Model Transcranial Magnetic Stimulation setup. Electrons flow through the magnetic head coil (yellow) producing a perpendicularly aligned magnetic field (dashed maroon circles), which in turn induces an electrical field (dashed green circle) below the surface of the brain. Credit: Eric Wassermann, M.D., via Wikimedia Commons
Transcranial magnetic stimulation (TMS) is arguably the most popular technique as a magnetic field can be used to influence brain activity without directly affecting sensory or pain fibers present in the scalp. An electric current is first passed through a metal circuit or “head coil” placed above the head (see right). Current flow through the coil induces the generation of a perpendicular magnetic field which can penetrate into the brain. This magnetic field in turn, creates an electrical field in the same plane as the coil, but below the surface of the brain. Depending upon the parameters employed by researchers this technique can be used to produce a relatively targeted excitation or inhibition of the underlying region of cortex.
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