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For those of you that are overly concerned/excited about this keep in mind that fMRI scans are kind of looked down upon the neuroscience research community for

For those of you that are overly concerned/excited about this keep in mind that fMRI scans are kind of looked down upon the neuroscience research community for the dubious misinterpretations from the findings (see dead Salmon fMRI study). It looks like PET imaging is what many are focusing their research into for better insight / “dynamic analysis” of the brain.

mikeiz404 4y ago
Dead Salmom fMRI Wired Article: https://www.wired.com/2009/09/fmrisalmon/ https://www.wired.com/2009/09/fmrisalmon/ Research Poster: http://www.prefrontal.org/files/posters/Bennett-Salmon-2009.pdf http://www.prefrontal.org/files/posters/Bennett-Salmon-2009....
ramraj07 4y ago
I know we haven’t proven fMRI is not truly measuring activity but have we proven it doesn’t even correlate?
- mattkrause 4y ago
  The signal measured by fMRI is definitely related to neural activity, but the relationship is indirect and sometimes subtly complicated. Neurons compute and communicate electrochemically by controlling how ions (charged particles) flow across their membranes. At "rest", the inside of a neuron is slightly negative (- 70 mV) relative to its environment. However, its surface is studded with channels that let different types of ions into/out of the cell as well as "receptors" that can open or close these channels. Some are opened by specific chemicals, which can bring the cell's membrane potential closer to zero (e.g., by admitting sodium ions). Once it gets above about -55 mV, other channels that are sensitive to voltage take over, and produce a wave of activity that shoots down the axon and eventually causes the release of chemicals that affect other neurons, muscles, etc. This is what actually does work in the brain, but it's not what fMRI measures. Instead, fMRI exploits the fact this process is energetically expensive: neurons need oxygen and sugar (glucose) to do all that work, and so neurons need to plumbed into the vascular system so those can be delivered. The signal fMRI measures is called the BOLD signal, for Blood Oxygenation Level Dependent. The magnetic properties of a blood molecule carrying oxygen are a bit different from a deoxygenated one, and thus they can be told apart with some clever physics and signal processing. Based on what I said above, you might expect that fMRI thus measures the reduction in oxygenation, but it actually turns out to be a lot more complicated than that. Levels do dip when nearby neurons are active, but only briefly. After that, they shoot up, above baseline levels: more blood--and more oxygen--are delivered to the formerly-active area. This is mostly what fMRI measures. The neuromuscular coupling seems to vary between brain states and maybe even brain areas; it's affected by different health conditions and drugs too. It's also limited by the structure of the vascular system. People occasionally find that veins appear to be heavily involved in cognitive tasks, sometimes even more than the brain itself, but that's just because they're delivering the blood. Despite all this, the mechanisms are getting better understood and you can certainly interpret a BOLD change as suggesting that something is happening in that particular region, even if it's not clear exactly how it's implemented.
mattkrause 4y ago
I'm sorry, but that's utter nonsense: fMRI is a perfectly legit technique (and it's not exactly interchangeable with PET). It is certainly true that there have been dubious and over-interpreted fMRI studies. As a technique, fMRI sits at a really awkward nexus where it is easy to do something but much harder to it well. Nevertheless, it can be done well. It just involves thinking hard about a lot of thorny problems, ranging from the signal itself (fMRI measures blood oxygenation, which is linked--indirectly--to neural activity), how it's measured, and how to analyze large volumes of data with unusual spatial and temporal correlation structures, plus the substantive research question on top! The only people who systematically look down on fMRI are insecure first year grad students who think their work is more "science-y" because it involves lasers or whatever rather than asking people about feelings. I guarantee you that many other fields (cough single-cell seq cough) have similar statistical problems; it's just fMRI hit them first and hit them hard: salmon-like mistakes are rare these days. As for PET, the ability to track things other than blood oxygenation is awesome, but the resolution is much worse and the radioactivity also limits its use. There is no magic tool; it's combinations that let us understand stuff.
- antegamisou 4y ago
  You’ve made some good points but just to clarify: I was stating what I perceived to be the general consensus among neuroscientists on fMRI (which btw makes the 'nonsense' labeling come off at least … unnecessary, if not rude) and since it seems PET imaging is on every study where various rates (glucose metabolism during RAPM testing is one iirc) are being measured during specific mental tasks subjects are submitted (or even studies on personality traits), I erroneously concluded fMRI had been 'grown out of' so to speak.
  - mattkrause 4y ago
    The “look down on it” bit hit a nerve because it is sort of true: there’s an archetype of bro-y “I do _real_ science” first year grad students who do think that. They (usually) grow out of it eventually, but usually not before demoralizing a classmate or two. I don’t think this is the general consensus among most neuroscientists though (I am one, but do neurophysiology rather than fMRI). Jack Gallant’s group, which I linked below, has produced a bunch of very smart people. There are some fMRI folks in the National Academy of Sciences, at the NIH, etc. It’s the real deal. I’m curious where you’re seeing newer glucose PET stuff. We have a radiochemistry group downstairs and I thought most of the excitement was now custom tracers for specific receptors.

mikeiz404 4y ago

Dead Salmom fMRI Wired Article: https://www.wired.com/2009/09/fmrisalmon/ https://www.wired.com/2009/09/fmrisalmon/ Research Poster: http://www.prefrontal.org/files/posters/Bennett-Salmon-2009.pdf http://www.prefrontal.org/files/posters/Bennett-Salmon-2009....

ramraj07 4y ago

I know we haven’t proven fMRI is not truly measuring activity but have we proven it doesn’t even correlate?

mattkrause 4y ago
The signal measured by fMRI is definitely related to neural activity, but the relationship is indirect and sometimes subtly complicated. Neurons compute and communicate electrochemically by controlling how ions (charged particles) flow across their membranes. At "rest", the inside of a neuron is slightly negative (- 70 mV) relative to its environment. However, its surface is studded with channels that let different types of ions into/out of the cell as well as "receptors" that can open or close these channels. Some are opened by specific chemicals, which can bring the cell's membrane potential closer to zero (e.g., by admitting sodium ions). Once it gets above about -55 mV, other channels that are sensitive to voltage take over, and produce a wave of activity that shoots down the axon and eventually causes the release of chemicals that affect other neurons, muscles, etc. This is what actually does work in the brain, but it's not what fMRI measures. Instead, fMRI exploits the fact this process is energetically expensive: neurons need oxygen and sugar (glucose) to do all that work, and so neurons need to plumbed into the vascular system so those can be delivered. The signal fMRI measures is called the BOLD signal, for Blood Oxygenation Level Dependent. The magnetic properties of a blood molecule carrying oxygen are a bit different from a deoxygenated one, and thus they can be told apart with some clever physics and signal processing. Based on what I said above, you might expect that fMRI thus measures the reduction in oxygenation, but it actually turns out to be a lot more complicated than that. Levels do dip when nearby neurons are active, but only briefly. After that, they shoot up, above baseline levels: more blood--and more oxygen--are delivered to the formerly-active area. This is mostly what fMRI measures. The neuromuscular coupling seems to vary between brain states and maybe even brain areas; it's affected by different health conditions and drugs too. It's also limited by the structure of the vascular system. People occasionally find that veins appear to be heavily involved in cognitive tasks, sometimes even more than the brain itself, but that's just because they're delivering the blood. Despite all this, the mechanisms are getting better understood and you can certainly interpret a BOLD change as suggesting that something is happening in that particular region, even if it's not clear exactly how it's implemented.

mattkrause 4y ago

I'm sorry, but that's utter nonsense: fMRI is a perfectly legit technique (and it's not exactly interchangeable with PET). It is certainly true that there have been dubious and over-interpreted fMRI studies. As a technique, fMRI sits at a really awkward nexus where it is easy to do something but much harder to it well. Nevertheless, it can be done well. It just involves thinking hard about a lot of thorny problems, ranging from the signal itself (fMRI measures blood oxygenation, which is linked--indirectly--to neural activity), how it's measured, and how to analyze large volumes of data with unusual spatial and temporal correlation structures, plus the substantive research question on top! The only people who systematically look down on fMRI are insecure first year grad students who think their work is more "science-y" because it involves lasers or whatever rather than asking people about feelings. I guarantee you that many other fields (cough single-cell seq cough) have similar statistical problems; it's just fMRI hit them first and hit them hard: salmon-like mistakes are rare these days. As for PET, the ability to track things other than blood oxygenation is awesome, but the resolution is much worse and the radioactivity also limits its use. There is no magic tool; it's combinations that let us understand stuff.

antegamisou 4y ago
You’ve made some good points but just to clarify: I was stating what I perceived to be the general consensus among neuroscientists on fMRI (which btw makes the 'nonsense' labeling come off at least … unnecessary, if not rude) and since it seems PET imaging is on every study where various rates (glucose metabolism during RAPM testing is one iirc) are being measured during specific mental tasks subjects are submitted (or even studies on personality traits), I erroneously concluded fMRI had been 'grown out of' so to speak.
- mattkrause 4y ago
  The “look down on it” bit hit a nerve because it is sort of true: there’s an archetype of bro-y “I do _real_ science” first year grad students who do think that. They (usually) grow out of it eventually, but usually not before demoralizing a classmate or two. I don’t think this is the general consensus among most neuroscientists though (I am one, but do neurophysiology rather than fMRI). Jack Gallant’s group, which I linked below, has produced a bunch of very smart people. There are some fMRI folks in the National Academy of Sciences, at the NIH, etc. It’s the real deal. I’m curious where you’re seeing newer glucose PET stuff. We have a radiochemistry group downstairs and I thought most of the excitement was now custom tracers for specific receptors.