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Give up? Do something else (bee keeping, perhaps)?

March 4, 2013

Screen Shot 2013-03-04 at 13.17.25

There’s a popular complaint out there that FMRI/MEG/EEG are correlational techniques, and so the patterns of activation we see may be by-products or epiphenomena. As such, FMRI/EEG/EEG may not tell us anything of interest about how the brain accomplishes tasks. Let’s take this position as a given and that there is a very real possibility that these are epiphenomena and so they are of limited use (NB the NeuroRant collective will point out how fundamentally stupid the epiphenomenon idea at a later date).

So what’s the solution? Give up? Do something else (bee keeping, perhaps)?

No. Never. Not this time. The solution is transcranial magnetic stimulation (TMS). TMS disrupts neural processes and so tells us if a region is NECESSARY for a given task (unlike grubby old FMRI which only shows it’s correlated with a task). Now TMS fixes everything, doesn’t it? For example, we zap motor cortex and motor output is disrupted. Ipso facto, the motor cortical region is necessary for motor output (like ranting). Great. Solved. Now we can get somewhere, right? Cure some neurological and psychiatric conditions? Get some Pulltizer prize-winning popular science books written, right? Wrong.

NeuroRant says: ‘Big Whoop’. We have established that a certain bit of the brain, X, is ‘necessary’ for process Y, but what have we learnt? What does being necessary mean? Does it mean that region X contains the neural representations that allows process Y to work? Not necessarily. Does it mean X is an important way-point, necessary for relaying information from brain region A to brain region B or down the spinal tract to make the body do something? Again not necessarily. Does it mean that region X modulates what region A does to allow A to do something important? Again not necessarily.

In fact, TMS-ing region X and so disrupting process Y could mean very, very many things, some of which are deeply uninteresting. In fact, you could imagine a really long daisy chain of processes that all have contributions on each other. So disrupting region X, disrupts process Z1 which disrupts process Z2 which disrupts process Z3 which disrupts process Z4, ad nauseum…  finally disrupting process Y. In fact this process could go on for ever, like might happen in a reductio ad absurdum. Oh, it is a reductio ad absurdum. Nice.

To illustrate, I might find that zapping my left medial-inferior-ventral-caudal-anterior-lateral-dorsal-parietal lobe increases the likelihood of me trolling strangers’ blog posts. This region is therefore necessary for stopping me irritating strangers. However, this may be deeply uninteresting. In actual fact (fact, in this thought experiment although unfortunately not in reality), this is because left medial-inferior-ventral-caudal-anterior-lateral-dorsal-parietal lobe actually is the part of the brain that allows bee-keeping thought processes to flourish. As everyone knows, bee-keeping, and thinking about such matters,  is an intensely calming persuit. If you stop this relaxing brain process then all sort of chaos starts churning around the brain. One thing leads to another, and it’s stranger-trolling time. The ‘necessary’ bit of TMS hasn’t really bought us anything about understanding how the brain works.

NeuroRant does not want to dismiss TMS as a useful technique. In fact, some of NeuroRant’s best friends are TMS-ers. However, NeuroRant isn’t convinced that TMS adds something, IN PRINCIPLE, very different to FMRI/MEG/EEG. It’s not better. It’s just a different approach with a different emphasis. That is, TMS could, in principle, all be neurobollocks in the same way that FMRI/EEG/MEG could be. Although, completely, blindingly, obviously BOTH techniques aren’t neurobollocks.

  1. Disclaimer: I’m a TMS-er

    I don’t agree. TMS can also be used to measure changes in cortical excitability, in inhibition or facilitation and in cortical reorganization. So yes, disrupting a process with TMS is not always useful but sometimes, this disruption is time-specific (which you don’t find in fMRI) which provides a lot of information.

    The problem is that, with fMRI, there will always be areas that will show up if you contrast a rest condition and a task condition. These areas are not very informative. It is not as easy with TMS. TMS disruption of a cortical area will not always yield a change in behavior. It is much more specific and requires a hypothesis-driven approach. This is less the case for fMRI (but depends on the experimental design)

    If you dismiss all virtual lesion studies, why not dismiss all lesions studies… It is true that the studies on HM are not very informative…

    So, no fMRI, no TMS and no lesion studies. What is left?

    The problem for any of those methods is not their use is how they are used. Nice and clever experimental designs are rare for TMS and for fMRI but these good experiments often provide a lot of information about how the brain works.

    • But we didn’t dismiss TMS. TMS is very useful. We said that at the end. And obviously, some uses of TMS (e.g., SICI) give completely different information to anything you can get with FMRI.

      What we were saying was that showing something is “necessary” is basically not telling us very much, in principle. Now it’s possible that TMS, for practical reasons, is better than FMRI. But that’s a completely different argument.

  2. I want to post a spelling rant: it is Ad NauseAM, you use the Latin inclinations the wrong way in more than one post. When you want to sound smart do it right.

    On topic: TMS or fmri arent the problem. Psychology is the problem. Mainly the lack of math and quantative system theoretical modeling. Disturbing a hypothesized network system and observing network response can learn one a great deal about a system. But that’s science, not psychology. Reasoning along the lines of ‘necessary’ processes and daisy chains is childish and unscientific.

    • A spelling error. we apologise. Although, for balance, there’s something not quite right about the word “quantative” in your post, and we’re not entirely sure that “learn” is used in the accepted way. But the meaning is clear enough, and that’s what’s important, right?

      Anyway, regarding the rest of your post, you seem to be agreeing with the gist of what we said. But, we wouldn’t go so far as to suggest that psychology is not science. Psychology is a broad field. There are some aspects of physics research which are a lot less scientific than many areas of experimental psychology.

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