How the brain increases blood flow on demand
hms.harvard.edu

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161 points

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gmays

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3 days ago

90 comments

evanjrowley ・ 3 days ago

Recently I started taking an angiotensin II receptor blocker as a medication to lower my blood pressure. The first week was difficult because my body couldn't significantly raise blood pressure during periods of sustained effort, like exercise and yardwork. I believe I'm over this now. Fortunately, the medication seems to be effective and I haven't experienced any negative side effects yet. Some people who take this medication have reported bad side effects, including "brain fog" while using it. I wonder if/how this medication might interact with the blood pressure control mechanisms observed in this research.

  • mediumrhino ・ 3 days ago

    I also take an angiotensin II receptor blocker and my experience has been similar. Additionally, I experience a perceived effect on stress levels as my pulse and blood pressure do not rise in stressful situations.

    On the negative side, I definitely have a harder time reaching my maximum pulse when working out.

  • gddgb ・ 2 days ago

    [flagged]

  • Danjoe4 ・ 2 days ago

    BP meds are dumb. Lose weight

    • mediumrhino ・ 2 days ago

      You assume that everyone has enough fat to shed to arrive at a desirable blood pressure. This is not the case.

    • thrawa8387336 ・ 2 days ago

      Worse, once you start it is very very hard to leave them

Insanity ・ 3 days ago

Always fascinating to me how we are brains, trying to understand how we work. Cool research!

  • SlowTao ・ 3 days ago

    "I used to think that the brain was the most wonderful organ in my body. Then I realized who was telling me this." - Emo Philips

  • kulahan ・ 3 days ago

    Along this same line of thought, I've always found it particularly fascinating that the universe is exploring the universe through molecules arranged into humans. Is the Universe the conscious one here?

    • hnuser123456 ・ 3 days ago

      What I never got is, why do we experience anything? Why can't the universe exist as a simulation where people do people things without having to consciously experience it all? Why can't I just shut off my experience and let my body do whatever it would do without having to put in effort, the same way everyone else's body does whatever it'll do without me having to experience everything they do?

      • groestl ・ 3 days ago
        ・ 3 more

        > why do we experience anything?

        Because the Essence that is the arrangement of molecules replicates onto other molecules, and it is more effective at replicating when it dedicates some of it's molecules to perceive and model it's own existence, in order to run experiments on it. That way it's more likely to find a behavior for the rest of the molecules to successfully replicate. So the molecules experience themselves, and the experience becomes more intense the more advanced the experiments are that can be run on the model.

        • phantompeace ・ 2 days ago
          ・ 2 more

          What is the Essence? In my head I picture movement or electrical fields propagating from some sort of proto cell like structure, but the more I try to “zoom” in, the more I try to find the finger that caused the ripple on the pond surface, so to speak

          • groestl ・ a day ago

            Just the arrangement, the structure, of the simpler things a system is made of, which allows a system to a) sustain and b) replicate.

      • rramadass ・ 3 days ago
        ・ 3 more

        The Hindu School of Philosophy named Samkhya/Sankhya gives you the appropriate Worldview in which your questions are answered - https://en.wikipedia.org/wiki/Samkhya

        There is an "Objective Reality" (mutable, evolves into many forms and includes both material/non-material concepts) and a "Witness-Consciousness" (immutable and attributeless). The latter is embodied in one form of the former which we call Sentient Living Beings. But we forget the distinction between the two and experience reality through its own subjective evolutes within the embodied being i.e. Sensory Mind, Intelligence and Ego. Various techniques/practices have been prescribed in Samkhya/Yoga/etc. to break out of this illusion and realize that one is simply pure awareness/consciousness beyond any experience. This is what is called as Kaivalya/Moksa/Nirvana i.e. a state of mind in which there is total freedom from everything to do with objective reality.

        See also the paper A landscape of consciousness: Toward a taxonomy of explanations and implications and previous discussion on it here - https://news.ycombinator.com/item?id=40844824

        • edwardbernays ・ 3 days ago
          ・ 2 more

          I have been reading the yoga sutras recently and it strikes me how applicable it is. The weird stuff about attaining magical powers is... cool, but samyama and the nature of the reflective consciousness have a lot of explanatory power imo.

      • exe34 ・ 3 days ago
        ・ 3 more

        My adopted working hypothesis is that we have to simulate what others observe/think in order to predict their behaviour and then adjust our own expectations and plans. It's a lo-fi model, because we don't have access to their internal workings - and yet it's a powerful model because it needs to predict the behaviour of very complex agents. If we then turn that powerful machinery onto ourselves, we can add all the extra information we didn't have of others. So it's a much richer, more detailed description of what's going on.

        It's not true that we have to be conscious - we can do things on autopilot too. The same way we can be thoughtless in treating others - we can turn the machinery off.

        • ccozan ・ 3 days ago
          ・ 2 more

          This autopilot works very well with a car and a very well known road ( like a daily commute).

          Recently I was thinking of a very hard problem and I cannot absolutelly recollect approx 30 minutes of the drive home. Apparently my body and some part of the brain took over the driving, while my cortex was busy with the problem reserving the short term memory completly. I snapped out of the situation when apparently a stronger break was needed, and this intrerupted my flow and popped my attention to the road. Fascinating!

          • Timwi ・ a day ago

            > Apparently my body and some part of the brain took over the driving

            That part of the brain is the cerebellum (mostly).

      • cantor_S_drug ・ 2 days ago
        ・ 2 more

        If you want to explore the future possibilities of that line of thought, then Greg Egan's Diaspora is good read.

        The Minds That Left Reality | Diaspora

        https://youtu.be/yYwqy4bzHG4

        • sweetheart ・ 2 days ago

          Such an incredible book! I read it like 8 years ago and think about it often enough that it was on my mind just yesterday :)

      • pessimizer ・ 3 days ago

        The two big problems: 1) Why is anything? and 2) Why am I here and you're over there?

      • gbrito ・ 2 days ago

        Isn't that what death is? No experience whatsoever. Unless the universe ends up being a closed system and we have this discussion or slight variations infinitely many times.

      • lithocarpus ・ 3 days ago

        There might be one like that out there but no one will know about it.

      • Cthulhu_ ・ 3 days ago

        > Why can't I just shut off my experience and let my body do whatever it would do without having to put in effort

        I do feel like most forms of leisure - watching / playing something, alcohol / drugs, sleeping - are basically this, you lose some of your consciousness and awareness in favor of what you're focusing on, or floating / free associating.

      • CoastalCoder ・ 3 days ago

        Friend, let me introduce you to the topics of philosophy, theology, and cosmology!

      • AlecSchueler ・ 2 days ago
        ・ 2 more

        How would your body react to stimuli without experiencing it?

        • Dumblydorr ・ 2 days ago

          Doctors use a hammer on the knee. Instinct and reflex is powerful, that’s why it exists down to amoebas and single celled organisms. A body that doesn’t have autonomic reactions isn’t going to reproduce as capably.

    • reactordev ・ 3 days ago

      I adopt the theory that all consciousness is energy vibrating the strings of the quarks that make up the atoms of the universe that make up humans that study the workings of the universe and thus, ourselves.

      A chorus of being.

      • teiferer ・ 3 days ago
        ・ 3 more

        Are you thus postulating that the rock next to me is as conscious as I am?

        That's a weird use of the term. Doesn't match how I would define it, but you do you.

        • reactordev ・ 2 days ago

          Yes but due to its density, it takes millions of years to form a sentence. If you listen closely to trees, they also speak with one another. Mountains do too. We just have the attention span of a gnat.

          I’m sure at some cosmic level there’s cities of marbles like ours just humming away.

    • exodust ・ 3 days ago

      Perhaps humans are not the end goal of the arrangement process. We like to think we are, but we're likely just a phase.

      • teiferer ・ 3 days ago
        ・ 8 more

        How come you are assuming that there is an "end goal"?

        Humans believing that they are special is as old as human history goes. Special as a species, but many groups also consider themselves special, and individuals as well. Seems to be an emergent thing from the human psyche. One that has had terrible consquences over the millenia, but I might be overlooking the upsides.

        • exodust ・ 2 days ago

          Because the process of "arranging" requires an end goal, according to the definition of the word. No assumptions needed.

          I was replying to the person who suggested the universe might be consciously exploring itself (goal) via an arrangement of molecules into humans. For fun, maybe the arranging process is at the beginning and the end goal is some kind of cosmic party after which everything resets again, or something.

        • johnisgood ・ 3 days ago
          ・ 6 more

          I think you are right. The "I am special" is rampant in today's society as well, and it causes a lot of harm, along with group thinking or mentality, us versus them, and so on.

          • kulahan ・ 2 days ago
            ・ 2 more

            Humanity is special. All evidence points to us being the only technological species in the universe. Way too many holes in the theories that aliens are simply hiding. If we aren’t in a zoo, we’re probably alone, and that in and of itself makes us special.

            But I should mention this PoV only works from an “all humans are equal” angle.

            • johnisgood ・ a day ago

              Yeah, I was referring to people who think they are special and others are not.

          • exe34 ・ 3 days ago
            ・ 3 more

            I am special. My friends say "he's a bit special."

            • johnisgood ・ 3 days ago

              I am special, too, according to many people. Special in the sense of being on the spectrum. :)

  • jimmygrapes ・ 3 days ago

    > Today a young man on acid realized that all matter is merely energy condensed to a slow vibration, that we are all one consciousness experiencing itself subjectively, there is no such thing as death, life is only a dream, and we are the imagination of ourselves. Heres Tom with the Weather.

    -Bill Hicks Don't take this as downplaying at all, because it's a fantastic and uplifting revelation, so long as one doesn't presume they're the first to consider it (it is even better this way imo)

  • motoboi ・ 3 days ago

    Are we though? If you look closely at it, there is no evidence that brain causes consciousness, just correlation.

    • WantonQuantum ・ 3 days ago

      There's a massive amount of evidence that consciousness occurs in the brain. If one were to propose that it's just a correlation then some kind of convincing argument would need to be made about how and why.

      • teiferer ・ 3 days ago

        I read GP comment as "there is no evidence that everything having a brain is conscious (and vice versa)", not as "the place where the individual's consciousness operates is the brain".

        The former could be applied to whatever LLM is the hype of the day.

        It's interesting though that the only consciousness that I'm sure of exists is my own. Anybody else's is just somehing I'm assuming. You can measure intelligence, but not consciousness.

      • nis0s ・ 3 days ago

        True, and there is also plenty of evidence which snows how neuronal degradation in some pathways leads to losing aspects of consciousness.

    • imchillyb ・ 2 days ago

      I believe there is thorough, observable, evidence to suggest that consciousness is manifest exclusively through the brain.

      Persons with damaged brains have damaged consciousness. Persons with underdeveloped brains have underdeveloped consciousness. People without functioning brains have no detectable consciousness.

      There is a metric ton of observed and collected data on consciousness.

      Of course evidence does not equal proof…

      • motoboi ・ 2 days ago
        ・ 2 more

        I appreciate your point, but be sure to take a look at the current state of the mind-body problem to understand that those evidences you brought up point to the brain as mediator of consciousness, not the cause.

        • Timwi ・ a day ago

          They absolutely point to the brain as the cause. To suggest otherwise is to introduce unscientific/superstitious concepts like souls or whatnot, which violates Occam’s razor. If that’s the road you want to go down, come back when you have independent evidence for that.

  • konfusinomicon ・ 3 days ago

    why did it name itself brain or whatever linguistic origin that brain is ultimately derived from. perhaps it was Brian and some brain out there made a typo and here we are today

    • treetalker ・ 3 days ago

      He's not the seat of consciousness — he's a very naughty boy!

  • grishka ・ 3 days ago

    A physicist is just atoms studying other atoms.

HardCodedBias ・ 3 days ago

Brain blood perfusion is quite amazing.

I don't understand from their research if

1) The the blood flow is following the computational/metabolic demand (via the endothelial cells communicating via gap junctions)

2) the brain is signaling the endothelial cells directly.

Maybe the paper explains it, or maybe more research required.

searine ・ 3 days ago

[flagged]

  • tomhow ・ 2 days ago

    Eschew flamebait. Avoid generic tangents.

    Please don't use Hacker News for political or ideological battle. It tramples curiosity.

    Please don't pick the most provocative thing in an article or post to complain about in the thread. Find something interesting to respond to instead.

    https://news.ycombinator.com/newsguidelines.html

  • Cthulhu_ ・ 3 days ago

    I wish / hope the rich take over what the government won't.

    edit: to a point of course, I don't want them pushing their agenda. Put money in an independent charity.

  • thrawa8387336 ・ 3 days ago

    It's great that they are still producing some quality research.

    • Aurornis ・ 3 days ago

      The articles you see now reflect research that was funded and started years ago.

      There will be a sudden and sharp decline in the amount of research produced going forward, until (hopefully) a new administration can make funding important scientific research a priority again.

  • andbberger ・ 3 days ago

    HHMI is a private org

    • lukas099 ・ 3 days ago

      So's Harvard Medical School, right? But they get research grants from the government?

      • nomel ・ 3 days ago
        ・ 3 more

        https://finance.harvard.edu/financial-overview

        Looks like they received $1 billion in private + government grants, so upper end would be 15%?

        > The University ended fiscal year 2024 with an operating surplus of $45 million compared to $186 million in fiscal year 2023, on an operating revenue base of $6.5 billion.

        Wow!

    • tylerhou ・ 3 days ago

      private orgs still benefit immensely from public funding because their researchers are by and large trained by public funding

  • tjwebbnorfolk ・ 3 days ago

    [flagged]

    • lawlessone ・ 3 days ago

      You don't like being reminded of the results of your decision?

      Not generalizing, i mean you specifically .

      • tjwebbnorfolk ・ 2 days ago

        I didn't vote for the orange nutjob any more than you. That doesn't mean I need to hear about his stupidity every 5 seconds on HN for absolutely no reason.

        The parent comment is completely irrelevant to the article. Downvote me all you want, I'm still correct.

    • mpalmer ・ 3 days ago

      I dunno, we're kind of upset about it. And why are you blaming GP? They aren't the one who forced politics into science.

    • tomhow ・ 2 days ago

      Their comment is against the guidelines and I've replied to them to point that out and also marked the subthread off-topic.

      But your reply also breaks the guidelines, notably this one:

      Please don't fulminate. Please don't sneer, including at the rest of the community.

      If you wouldn't mind reviewing https://news.ycombinator.com/newsguidelines.html and taking the intended spirit of the site more to heart, we'd be grateful.

    • exe34 ・ 3 days ago

      There's a reason people hate talking about politics and religion. They are the two forces that shape everything we are allowed to do, so we should not be allowed to talk about them!

    • angelgonzales ・ 3 days ago

      Totally support you!

      I have done research and analysis long enough to understand that we all need to remain humble and refrain from assuming a conclusion without substantial evidence.

      When I read the sentence “All of which have had deep funding cuts.” I speculate that this response is a simple signal amplification without any added evidence and without critique. I think it’s an attempt at self and collective affirmation.

      Who is to say that funding cuts in academia won’t have short and long-term benefits for society and also result in a net increase in happiness and productivity? We simply don’t know yet. Supply and demand of valuable thought and research may redistribute within the economy!

      I think there are very political people out there, the world may benefit from forums which cater to people who are political and separately to those who aren’t very political!

      • ivell ・ 3 days ago

        >> Who is to say that funding cuts in academia won’t have short and long-term benefits for society and also result in a net increase in happiness and productivity

        Don't we already have evidence of this? Many developing nations do not have adequate funding for academia and it is not increasing their happiness and productivity. Neither we can see any benefits on the society.

      • teiferer ・ 3 days ago
        ・ 10 more

        > Who is to say that funding cuts in academia won’t have short and long-term benefits for society and also result in a net increase in happiness and productivity

        Who is to say that if I stop eating I won't see long-term benefits and also result in a net increase in happiness and productivity?

        • vntok ・ 3 days ago
          ・ 9 more

          > Who is to say that if I stop eating beef I won't see long-term benefits and also result in a net increase in happiness and productivity?

          See how considering the tiniest amount of nuance instead of oversimplifying everything tends to allow more interesting thought patterns?

          • teiferer ・ 2 days ago
            ・ 8 more

            Does it? The point was that stopping calorie intake leads to death. That's not a controversial statement. Stopping funding is similar, it ends the thing it used to fund. Expansion of human knowledge, in this case.

            Unclear what that would have to do with beef. Are you saying that beef is bad for health, so stopping only that from entering your mouth is good for your health, and similarly, academic research is bad, so ending that could be good for society? Which type of research is better for society, assuming you'd like to keep some way for society to expand its knowledge of the world?

            • vntok ・ 2 days ago
              ・ 7 more

              In your own allegory, stopping calorie intake would be akin to defunding " Science ". Obviously that brings death to the body and brain drain to the country, no one disputes this I think.

              But that's not what is happening here, so I'm not sure why you would choose to use this allegory.

              Indeed, cutting 100% of gov funding to Harvard Medical School results in defunding them by 20% or so. In your own allegory, that would be akin to reducing calorie intake of a particular type of meat (say, beef) but only by 20% . So: is it bad over the long term? Meh, who knows? It's not trivial to answer, right?

              • freejazz ・ 2 days ago

                Do you have any reason to actually support this kind of otherwise completely specious argument? Yeah, sure, limiting some things that are not good can make a good result. Where's the leap from that to the medical research that's being stopped?

              • teiferer ・ 2 days ago
                ・ 5 more

                > So: is it bad over the long term? Meh, who knows? It's not trivial to answer, right?

                There are two statements here:

                1. Your "who knows if medical research funding being severely reduced will lead to a worse outcome in terms of research results; not trivial right?"

                2. My "reducing funding of medical research will have a negative impact on research results."

                It's not hard to argue that the first one is the claim that has the burden of proof.

                • vntok ・ 2 days ago
                  ・ 4 more

                  I do not agree with your postulate that funding any medical research necessarily brings "long-term benefits for society and also result in a net increase in happiness and productivity".

                  Surely that needs proving. And it seems quite hard for the argument trivially collapses if said research is done by incompetents who misinterpret results, is done by frauds who fake the results, or if the money given is squandered isntead of researching, or if the research results are not written down and shared.

                  • teiferer ・ 15 hours ago
                    ・ 3 more

                    And you are saying that those misuses of money were happening at Harvard?

                    Must be really easy to get a research position there if every idiot fraud is able to.

                    • vntok ・ 12 hours ago
                      ・ 2 more

                      > And you are saying that those misuses of money were happening at Harvard?

                      Out of a more than $2.6B research grant package, yes I do feel pretty certain that there's some misuse happening. Don't you? Misuses of money routinely happen in all sorts of places on much much lower amounts of grants/donations, so what do you think makes Harvard immune to it?

                      There's also the fact that the institution seems open to settling, an indicator among others that they aren't confident in their ability to sustain an audit (per the NYT: "Harvard Is Said to Be Open to Spending Up to $500 Million to Resolve Trump Dispute" https://www.nytimes.com/2025/07/28/us/politics/trump-harvard...)

                      > Must be really easy to get a research position there if every idiot fraud is able to.

                      Indeed. Presumably this is a reason for the Trump admin's demand that Harvard turn over employment forms for university staff. The good news is that Harvard seems to be complying (per The Guardian: "Harvard to comply with Trump officials’ demand to turn over employment forms" https://www.theguardian.com/education/2025/jul/29/harvard-tr...), so if there's anything the admin disagrees with we're sure to hear all about it soon.

                      • teiferer ・ 43 minutes ago

                        Hm interesting. You seem to assume that cutting funding by 20% will cut exactly the fraudulent parts. That naïve world view is quite impressive tbh.

                        >> Must be really easy to get a research position there if every idiot fraud is able to.

                        > Indeed. [...]

                        Hm alright. About 10 of my friends have tried over the years to get into Harvard for research positions, only 2 of them succeeded. I must be surrounded by stupid idots then. Not clear to me how the rest of your text provides any supporting argument (what does providing employment forms have to do with it?) but I'm likely just as stupid as my friends.

      • freejazz ・ 3 days ago

        Obtuse and naive.