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28 November 2014 @ 10:26 am
fMRI  
Had a Thanksgiving dinner that couldn't be beat yesterday, and had lots of fine conversation with some of our oldest fannish friends. It was a good time. We will get through this.

I had wondered what happened during the functional MRI. Kate said that there was first a general MRI (just holding still while the machine banged and thumped), then a finger-tapping exercise (tap a finger for 30 seconds, then hold still, then tap again), then an exercise of nouns and verbs (given a noun, think of the corresponding verb), then an exercise of concrete/abstract (given a verb, think of whether it is concrete or abstract), then another exercise she doesn't recall. It was all kind of boring and repetitive and some of the tests had to be done over because she dozed off, though they still finished it all up in just under the scheduled two hours.

The answer to the question "how is it that they can ask if you are claustrophobic and also say that you have to be able to read text five feet away??" is that she had an angled mirror in front of her eyes and the words were shown to her on paper cards (some printed, some hand-lettered) held up near her feet.

The paper cards and hand-lettering tell me that the tests vary a lot depending on exactly what brain areas are being examined for the particular patient, and also that this is a very new type of test. This also suggests a reason for the whole deal with the contact lenses -- they are still figuring out how to effectively administer this test. Perhaps in five years the prompts will be displayed on a screen and they'll have a rack of glasses with all-plastic frames in a variety of common prescriptions.

I'll just leave you with today's XKCD:

 
 
 
A Wandering Hobbitredbird on November 28th, 2014 07:02 pm (UTC)
That xkcd is very apropos. Do you know Randall, or is this synchronicity?
David D. Levinedavidlevine on November 29th, 2014 05:58 am (UTC)
Just synchronicity, as far as I know.
Kate Schaeferkate_schaefer on November 28th, 2014 07:24 pm (UTC)
We had a similar Thanksgiving dinner yesterday, with a certain amount of glass-raising to absent friends and slightly over-emphatic hugging of present friends.
tandwtandw on November 28th, 2014 11:22 pm (UTC)
That setup reminds me of when we needed to have our son's visual acuity checked...when he was something like six months old. The process involved sitting him down in front of a monitor in a room full of rack-mounted electronics, putting electrodes on his head to measure neural activity in the visual cortex, and showing arrays of stripes on the monitor that got progressively narrower. When he stopped being able to resolve them as stripes, his visual cortical activity dropped off, and knowing the distance from his eyes to the monitor let the doc determine his angular visual acuity.

The cool part was when the doc checked whether he was fusing the images from his right and left eyes. The doc put a pair of glasses on him, one red lens and one green lens, flashed a circle on the monitor--eight Hz red and 6 Hz green--and did a Fourier transform on his visual cortical activity. You could see the 1/6 and 1/8 periodicities very clearly on the transformed plot, and a little bitty bump at 1/14 that was the image fusion.

This was over nineteen years ago, so I'm sure that the setup is much cleaner these days. Haven't had any occasion to see eye tests of preverbal children, though.
David D. Levinedavidlevine on November 29th, 2014 05:59 am (UTC)
That's fascinating! I had wondered how they assess babies' vision and hearing.
tandwtandw on November 30th, 2014 04:43 pm (UTC)
For a quick and dirty estimate of prescription, there's the much less involved "hold up a lens to the kid's eye and see how sharp the retinal image is" method, but in the case of our son the docs were concerned about how well he was actually processing things.

It occurs to me that you could do something similar for a hearing test; sound a tone at various pitches with an on/off component (i.e., silence/tone/silence/tone) with the silence/tone switches coming at say 6x/second. Do a Fourier transform on auditory cortical activity and look for the 1/6 peak, and drop the volume to see where the peak goes away. Probably been done, though.
Josephthe_gardener on November 28th, 2014 11:35 pm (UTC)
Interesting -- when I was sent for my MRI scan this summer (because the hospital consultant wanted to rule out a head or neck injury as the cause of the loss of motor nerve impulses in my left arm) I was instructed to lie absolutely still and think of nothing at all for the half-hour I was in the machine. I dozed off too -- they had to wake me up when they'd finished.
Luke McGuffholyoutlaw on November 29th, 2014 07:34 pm (UTC)
The one time I had an MRI (several years ago, working out the Meniere's diagnosis) I thought "I used to buy albums that sounded like this." I don't remember if I dozed off or not.
tandwtandw on November 30th, 2014 04:34 pm (UTC)
Someone (can't remember who) said they kept trying to fit the beat to the opening bars of "They're Coming to Take Me Away, Ha-Ha!"