28 ms·

The optic nerve is directly connected to the superior colliculus, which directly controls saccades and is sensitive to novel (bright) visual stimuli. If such a

The optic nerve is directly connected to the superior colliculus, which directly controls saccades and is sensitive to novel (bright) visual stimuli. If such a stimulus hits the the periphery just outside the fovea the time from stimulus onset to "fixation" should be minimized, without having to go through the "slow" ventral pathway/stream (V1 etc.). This time should still be more than 1-3 ms, but likely is below 100ms. No references, sorry. Edit: First said LGN projects SC, but pathway is even shorter than that. Edit2: The consensus on these fast, superior colliculus-guided "Express" saccade latency seems to be 80-120 ms. See: http://www.scholarpedia.org/article/Human_saccadic_eye_movements http://www.scholarpedia.org/article/Human_saccadic_eye_movem...

nonbel 9y ago
Why is there so much expertise being shared without any refs on this topic? Are they hard to find online for some reason?
- Phemist 9y ago
  One of the issues is this type of neuroscience is becoming too "basic", so it's what gets taught in classes as the truth and professors don't necessarily give references anymore. Also I was typing on my mobile phone, but have switched to my laptop now. The scholarpedia (basically peer-reviewed wikipedia) article on saccades should be pretty interesting.
  - ant6n 9y ago
    If it's very basic, the reference could be a text book.
    - Phemist 9y ago
      Ofcourse, but textbooks are super-broad in scope. I don't think just referencing "Kandel, 5th edition" would be of much help and I don't have these books on hand to actually point you to the right page/section of the book.
    - nonbel 9y ago
      I wouldn't trust a textbook, they usually leave out the nature of the evidence for whatever is being claimed (not even citing sources). You really have to get to the primary literature. For example, this sounds factual enough: "The optic nerve is directly connected to the superior colliculus" But I wonder how this "direct connection" was established. Was it done in humans or only mice/rats? Is it really always a direct connection or only in eg 80% of people, etc.
      - Balgair 9y ago
        https://www.amazon.com/Principles-Neural-Science-Fifth-Kandel/dp/0071390111 https://www.amazon.com/Principles-Neural-Science-Fifth-Kande... This is a good text, at an upper-div/grad level, of fundamental neuroscience with all sources cited. That particular connection is straightforward to do in humans. A Golgi stain to the rector muscles/ON and dissection in cadavers would be sufficient to trace the reflex to the SC and then another Golgi stain to that area to get back to the optic nerve. I'm unfamiliar with the toxicity of Golgi stains, but it may be able to be done alive. Also, the visual systems to the brain-stem are remarkably conserved through evolution. I would not be surprised to see this connection in lampreys. That any significant percent of humans lack it would be a hell of paper. Blind individuals usually have these reflexes too (like Stevie Wonder): https://en.wikipedia.org/wiki/Blindsight https://en.wikipedia.org/wiki/Blindsight
        nonbel 9y ago
        >"This is a good text, at an upper-div/grad level, of fundamental neuroscience with all sources cited." I was able to check a bit and see no citations: "The human brain contains a huge number of these cells, on the order of 10^11 neurons, that can be classified into at least a thousand different types." https://neurology.mhmedical.com/content.aspx?bookid=1049&sectionid=59138622 https://neurology.mhmedical.com/content.aspx?bookid=1049&sec... That 10^11 number is out of thin air. How was it determined? That is what a citation is for. >"I'm unfamiliar with the toxicity of Golgi stains, but it may be able to be done alive." No, the gogli stain is very toxic. It depends on a precipitate forming in "random" (no one knows why) cells. Also I see no reason it couldn't spread from cell to cell (via gap junctions, etc) so that method isn't too convincing. >"Also, the visual systems to the brain-stem are remarkably conserved through evolution." You can remove a rat's cerebrum and have it stay alive and keep doing stuff: "Cage climbing, resistance to gravity, suspension and muscle tone reactions, rhythmic vibrissae movements and examination of objects with snout and mandible were difficult to distinguish from controls." https://www.ncbi.nlm.nih.gov/pubmed/630411 https://www.ncbi.nlm.nih.gov/pubmed/630411 Rodents are much more reliant on their brainstem than humans, I wouldn't be at all surprised that there are large differences. In fact, there's been a long debate about a similar claim regarding the cortico-spinal tract: "Direct connections between corticospinal (CS) axons and motoneurons (MNs) appear to be present only in higher primates, where they are essential for discrete movement of the digits. Their presence in adult rodents was once claimed but is now questioned." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704511/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704511/
    - kkylin 9y ago
      Ideally. Problem is, things move too quickly to get into textbooks or even review articles, especially on the experimental side of things. I'm not a neuroscientist myself, and have cobbled together what little I know from books (which I read but do not always trust), papers (which are not always easy for outsiders to interpret), and most importantly talking to neuroscientists, participating in / co-running journal clubs, etc.
Phemist 9y ago
So in response to the grandparent, 1-3 ms is way too short, but it kinda of depends on the definition of "react" in this instance. The delay from a photon hitting the retina to triggering neurons in the superior colliculus to spike is likely pretty low (I would guess ~10 ms?), but when ocular motor movement becomes involved (ie stimulus onset -> fixation) things slow down considerably.
kkylin 9y ago
Cool, thanks!

nonbel 9y ago

Why is there so much expertise being shared without any refs on this topic? Are they hard to find online for some reason?

Phemist 9y ago
One of the issues is this type of neuroscience is becoming too "basic", so it's what gets taught in classes as the truth and professors don't necessarily give references anymore. Also I was typing on my mobile phone, but have switched to my laptop now. The scholarpedia (basically peer-reviewed wikipedia) article on saccades should be pretty interesting.
- ant6n 9y ago
  If it's very basic, the reference could be a text book.
  - Phemist 9y ago
    Ofcourse, but textbooks are super-broad in scope. I don't think just referencing "Kandel, 5th edition" would be of much help and I don't have these books on hand to actually point you to the right page/section of the book.
  - nonbel 9y ago
    I wouldn't trust a textbook, they usually leave out the nature of the evidence for whatever is being claimed (not even citing sources). You really have to get to the primary literature. For example, this sounds factual enough: "The optic nerve is directly connected to the superior colliculus" But I wonder how this "direct connection" was established. Was it done in humans or only mice/rats? Is it really always a direct connection or only in eg 80% of people, etc.
    - Balgair 9y ago
      https://www.amazon.com/Principles-Neural-Science-Fifth-Kandel/dp/0071390111 https://www.amazon.com/Principles-Neural-Science-Fifth-Kande... This is a good text, at an upper-div/grad level, of fundamental neuroscience with all sources cited. That particular connection is straightforward to do in humans. A Golgi stain to the rector muscles/ON and dissection in cadavers would be sufficient to trace the reflex to the SC and then another Golgi stain to that area to get back to the optic nerve. I'm unfamiliar with the toxicity of Golgi stains, but it may be able to be done alive. Also, the visual systems to the brain-stem are remarkably conserved through evolution. I would not be surprised to see this connection in lampreys. That any significant percent of humans lack it would be a hell of paper. Blind individuals usually have these reflexes too (like Stevie Wonder): https://en.wikipedia.org/wiki/Blindsight https://en.wikipedia.org/wiki/Blindsight
      - nonbel 9y ago
        >"This is a good text, at an upper-div/grad level, of fundamental neuroscience with all sources cited." I was able to check a bit and see no citations: "The human brain contains a huge number of these cells, on the order of 10^11 neurons, that can be classified into at least a thousand different types." https://neurology.mhmedical.com/content.aspx?bookid=1049&sectionid=59138622 https://neurology.mhmedical.com/content.aspx?bookid=1049&sec... That 10^11 number is out of thin air. How was it determined? That is what a citation is for. >"I'm unfamiliar with the toxicity of Golgi stains, but it may be able to be done alive." No, the gogli stain is very toxic. It depends on a precipitate forming in "random" (no one knows why) cells. Also I see no reason it couldn't spread from cell to cell (via gap junctions, etc) so that method isn't too convincing. >"Also, the visual systems to the brain-stem are remarkably conserved through evolution." You can remove a rat's cerebrum and have it stay alive and keep doing stuff: "Cage climbing, resistance to gravity, suspension and muscle tone reactions, rhythmic vibrissae movements and examination of objects with snout and mandible were difficult to distinguish from controls." https://www.ncbi.nlm.nih.gov/pubmed/630411 https://www.ncbi.nlm.nih.gov/pubmed/630411 Rodents are much more reliant on their brainstem than humans, I wouldn't be at all surprised that there are large differences. In fact, there's been a long debate about a similar claim regarding the cortico-spinal tract: "Direct connections between corticospinal (CS) axons and motoneurons (MNs) appear to be present only in higher primates, where they are essential for discrete movement of the digits. Their presence in adult rodents was once claimed but is now questioned." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704511/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704511/
  - kkylin 9y ago
    Ideally. Problem is, things move too quickly to get into textbooks or even review articles, especially on the experimental side of things. I'm not a neuroscientist myself, and have cobbled together what little I know from books (which I read but do not always trust), papers (which are not always easy for outsiders to interpret), and most importantly talking to neuroscientists, participating in / co-running journal clubs, etc.

Phemist 9y ago

So in response to the grandparent, 1-3 ms is way too short, but it kinda of depends on the definition of "react" in this instance. The delay from a photon hitting the retina to triggering neurons in the superior colliculus to spike is likely pretty low (I would guess ~10 ms?), but when ocular motor movement becomes involved (ie stimulus onset -> fixation) things slow down considerably.

kkylin 9y ago

Cool, thanks!