Confederacy of a Dunce - Stirring the brain

Friday, November 11, 2005

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It's been a very busy week; I'm in the midst of preparing an extensive application to obtain ethical approval for several years' future experiments in language processing and cognitive neuroscience. I don't write much at all about specific things I'm doing at work, mainly because my work-related writing is channeled toward more practical ends like publications, applications and a minor project known colloquially as a Ph.D. thesis.

But when it comes to messing around with people's brains, how could I not write about it? I'm talking, of course, about Transcranial Magnetic Stimulation (TMS). TMS is a way of directly affecting the brain by using directed magnetic devices on the surface of the head, in order to induce electrical currents in fairly precisely-identified areas of the brain (at least on areas near the surface). The main concern is safety: the International Federation of Clinical Neurophysiology reports safety considerations (most importantly, avoiding TMS if you have metal in your head, sensitive implanted electronic devices, epilepsy, heart disease, etc.). Anyway, TMS has generally been used for two main purposes. First, as a treatment for depression (see this psycom.net link for more details), essentially as a safer, less invasive and generally nicer version of electroconvulsive therapy. I know little about this research, but there is a lot of interest in this application, although to date the US FDA has not approved TMS devices for use in therapeutic settings (some have been approved by similar bodies in Canada and Israel).

The area I'm involved in, instead, focuses on trying to gain a better understanding of brain function by assessing the effects of TMS upon a specific part of the brain. The logic here is fairly simple: if a particular part of the brain is involved in processing information of a certain kind, TMS to that area will affect tasks that involve that kind of information. For example (a fake example using entirely invented areas and ideas, but which is very much an analog to the real studies we are considering), suppose that we are testing a hypothesis that the Ultramarine area of the brain is responsible for performing mathematical operations of addition and subtraction. A TMS experiment might then test participants' ability to add and subtract under different stimulation conditions: No stimulation at all (to get an idea of each participant's different abilities), stimulation to the Ultramarine area, and stimulation to the Periwinkle area (which is not believed to be involved in adding and subtracting). If the Ultramarine area is indeed involved in adding and subtracting, we would expect to see differences when comparing performance between the Ultramarine and Periwinkle stimulation conditions. Such differences are not enough to allow conclusions that indeed, the Ultramarine area is involved in addition and subtraction (for example, it could be involved in all mathematical operations, or in combinatorial processes of all sorts, or in visual recognition processes, or "cognition", or numerous other things the brain can do). In order to make conclusions like that, it's also necessary to conduct similar experiments using different tasks (for example, multiplication and division, for which differences would not be observed if the Ultramarine area is only doing addition and subtraction). This is especially important (and difficult) since many areas of the brain seem to subserve multiple functions, and it's extremely hard to isolate specific functions. Think of everything that is involved in doing a simple addition problem like 2+2. Seeing the image of "2+2", distinguishing the individual numbers and symbols as distinct entities, identifying the referent of each (i.e. "+" means to add), retrieving or calculating the answer (however that is done!), and all the steps involved in producing the answer (let me assure you, there are many). In short, it's a hard problem that requires many, many steps.

Yesterday for the first time, I participated in a TMS experiment. Unfortunately, it didn't go so well, despite all my knowledge about the relative safety of TMS, and also my knowledge that the particular area being stimulated (visual area V1) is not typically a painful or unpleasant site (other sites can have uncomfortable consequences, such as an icky twitch of the facial muscles each time a magnetic pulse occurs). I blame it on the fact that I am a delicate flower of a man. It was a rather strange sensation, somewhat like someone tapping on the back of my head. But I managed to work myself into a sort of state (quite similar to my reaction to blood tests or other medical situations): by about trial number 10 (of 150+) I was shaking, sweating profusely, light-headed and nauseated, and I had to call a stop to it. I'm afraid I'll have to wear my tinfoil hat into the TMS lab in the future.

science

Friday, November 11, 2005 1:33:13 PM (GMT Standard Time, UTC+00:00)

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Thursday, November 17, 2005 1:00:03 PM (GMT Standard Time, UTC+00:00)

According to your fake analog experimental setup, trial number 10 should still have been assessing your 'mathematical' ability before any stimulation had occurred. Perhaps you are trying to blame TMS for your inadequate 'mathematical' skill. Of course, since you don't share the actual nature of the experiment, we all know that it must be. nudge nudge

The Noblesvillian

Thursday, November 17, 2005 1:05:46 PM (GMT Standard Time, UTC+00:00)

Dear Sir,

I should note that in my fake analog experiment setup, my description was not intended to reflect the actual order of stimulation (or no-stimulation types). In actuality, all possible orders would be used (for different participants) in order to rule out the possibility that increased or decreased performance was related to the stimulation itself, rather than to fatigue or practice effects.

Sorry for failing to clarify this; I think it qualifies as an error of omission rather than a mathematical error.

The Dunce

Sunday, November 20, 2005 2:13:35 AM (GMT Standard Time, UTC+00:00)

I guess that's what I get for trying to use a flux capacitor as a random-number generator.

The Noblesvillian