How the brain increases blood flow on demand
60 comments
·July 29, 2025evanjrowley
mediumrhino
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.
Insanity
Always fascinating to me how we are brains, trying to understand how we work. Cool research!
SlowTao
"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
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
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?
Cthulhu_
> 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.
groestl
> 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.
tasty_freeze
David Chalmers coined the phrase "the hard problem" of consciousness.
lithocarpus
There might be one like that out there but no one will know about it.
CoastalCoder
Friend, let me introduce you to the topics of philosophy, theology, and cosmology!
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exe34
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.
pessimizer
The two big problems: 1) Why is anything? and 2) Why am I here and you're over there?
reactordev
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
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.
exodust
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
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.
motoboi
Are we though? If you look closely at it, there is no evidence that brain causes consciousness, just correlation.
WantonQuantum
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
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
True, and there is also plenty of evidence which snows how neuronal degradation in some pathways leads to losing aspects of consciousness.
grishka
A physicist is just atoms studying other atoms.
konfusinomicon
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
He's not the seat of consciousness — he's a very naughty boy!
jimmygrapes
> 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)
bozhark
So you can get brain hard?
crackrook
You can get nose hard too! https://wikipedia.org/wiki/Honeymoon_rhinitis
searine
Supported by the National Science Foundation, Harvard Medical School, National Institutes of Health, and the Howard Hughes Medical Institute.
All of which have had deep funding cuts.
Cthulhu_
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
It's great that they are still producing some quality research.
Aurornis
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
HHMI is a private org
tylerhou
private orgs still benefit immensely from public funding because their researchers are by and large trained by public funding
lukas099
So's Harvard Medical School, right? But they get research grants from the government?
nomel
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!
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searine
"HHMI halts inclusive science programme" : https://www.nature.com/articles/d41586-025-00396-6
tjwebbnorfolk
There had to be someone who couldn't help themselves but to bring politics into this somehow.
We all read the news. Everyone knows this. Is there no escape even on HN? Just shoot me already.
lawlessone
You don't like being reminded of the results of your decision?
Not generalizing, i mean you specifically .
mpalmer
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.
exe34
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!
Bluescreenbuddy
Leave if you don’t like it. Whiny child
angelgonzales
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!
teiferer
> 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?
ivell
>> 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.
freejazz
Obtuse and naive.
HardCodedBias
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.
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.