Transcranial Magnetic Stimulation (TMS) - a breakthrough in brain science
By Mike Hanlon
February 12, 2006
This article is the latest in a monthly series by Dr. Max Sutherland. Max’s column is published monthly and posted at sutherlandsurvey.com. You can receive an advance copy by email (it's free). Max Sutherland is author of the book 'Advertising & the Mind of the Consumer’ (published in eight languages) and is a registered psychologist. He works as an independent marketing consultant in Australia and USA and is also Adjunct Professor at Bond University.
February 13, 2006 Everyone knows about brain scanning, but most of us have never heard of a new technology called transcranial magnetic stimulation (TMS). Non invasive and painless, it can temporarily inactivate an area of the human brain to let brain scientists study the effect. Twenty years ago we began the scientific dream of peering into the human brain while it is working. Brain scanning devices such as fMRI and PET scans can pinpoint precisely which brain regions are active as people respond to stimuli (including brands and advertisements) or as they go about making decisions (including brand choices). It is fascinating to see just what areas of the brain light up in response to a stimulus or a particular decision task but still we have to ask, what exactly can we conclude from this? Because an area of the brain lights up doesn’t mean that it is causal in that behaviour or decision. After all, ice cream sales correlate with drownings but they don’t cause them. You cannot conclude causality from correlation because there is no way of knowing if some other, unaccounted-for variable (like weather) may be involved. To sort out causality you need to be able to do experimentation.
Brain scientists must do more than just observe the brain at work; they have to be able to experiment on it, but there are definite limits to the extent that brain scientists can intervene with, and physically play around in, someone’s brain.
Now, this limitation has been partly lifted by a breakthrough in technology in the form of a device that can harmlessly and temporarily knock out targeted brain areas and thereby help brain scientists sort out causality. It is called Transcranial Magnetic Stimulation (TMS).
TMS uses a powerful magnetic field to stimulate or inhibit areas of the brain. It requires the generation of an electromagnetic signal at a specific frequency, and a coil to focus that magnetic field on a specific brain region. The stimulating coil is held close to the scalp so that the field is focused and can pass through the skull. What is felt is merely a kind of tapping on the skull as the current starts to flow.
The magnetic field used in TMS can temporarily knock out a brain function or artificially stimulate one. It appears that low frequencies (lower than 1 Hz) inhibit brain activity, while higher frequencies stimulate the targeted brain area, although no one is sure why. After magnetic stimulation of a brain region, even at higher frequencies, an area usually becomes temporarily unresponsive to the normal input from the rest of the brain. So with this newer technology, instead of merely watching the brain in action, experimenters can intervene to transiently inactivate an area and evaluate the behavioural consequences. This enables researchers to more easily test hypotheses about the human brain.
Although TMS devices have been around since 1985, it is only recently that it has become possible to use TMS simultaneously with other brain scanning techniques. It can now be used in combination with these, and this means we can examine the brain at work with (fMRI or PET) brain scanning while simultaneously applying TMS to knock out a key brain area and watch the effect. In other words, it gives us more in insight as to what role that part of the brain seems to be playing.
A Potential Therapeutic Tool
TMS is more than an exciting research tool; it is also shaping up as a treatment tool for some psychological problems. For example, by applying it to the temporal lobes (just above the eyebrows) it alters a person’s mood. Applying it above the right eyebrow produces euphoric happiness while above the left eyebrow produces apathy and sadness. There is considerable research under way to turn this from a temporary effect into a longer lasting treatment for depression.
People understandably worry about the prospects of mind control with such brain science techniques and their fears seems justified when claims for the techniques are subjected to commercial hype often by consultants wanting to sell their services. TMS is currently only possible if a volunteer’s head is in close contact with the magnetic source so why should we be afraid of mind control with it? The answer according to Steven Rose, the noted British professor of biology writing in The Observer (5th Feb. 2006), is that TMS at a distance is now under active military investigation.
TMS can be used to prevent people from seeing a visual stimulus, make it hard for them to speak, or induce involuntary movements. Pulses directed to different spots on the motor cortex can make a thumb twitch, an arm jerk, or a leg kick. If TMS application at a distance becomes a possibility, it could potentially be used by the military to disable an enemy by controlling their mood, vision, or physical responses.
It is also easy to see how it could be used unscrupulously …