
Electrical properties of dendrites help explain our brain’s computing power - magoghm
http://news.mit.edu/2018/dendrites-explain-brains-computing-power-1018
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Symmetry
They're comparing human brains to rodent brains here. Suzana Herculano-Houzel
did some interesting work recently that showed that human (and primate, and
bird) brains have neuron counts that scale linearly with volume while most
mammals only scale something like the 3/4 power of volume. So I wonder how a
crow or lemur brain would look in this regard.

~~~
Balgair
Dr. Herculano-Houzel is a real life Indiana Jones of the brain. She's an
absolute jewel in science. I remember her telling a group of us about her
efforts in Botswana(?) to get elephant brain specimens. Normally, to preserve
a brain, you pump fixative in via the arteries at low concentrations. Even in
a mouse, this takes a few hours. For megafauna, it can take a few days. To get
good elephant data, she told us that you have a new problem: scavengers. You
take the elephant (per game-park regulations) and then get the skull off and
gain access to the massive arteries. Then you have to find a tall enough tree
to hang fixative from, as you can't get a pump out into the veld that will run
for days. You just have to let gravity do the work. Then you slowly fix the
brain in the skull in some random place in the bush. However, the rest of the
elephant is very good at attracting lions, hyenas, etc at all hours of the
day. So you have to fend off the skull from very hungry predators. It's not a
'fun' experience, in her recollection. I remember something about 4-bore
rifles being used a fair bit. Finally you have to get the brain out of
country, which, depending on international regulations and local bribery
customs, can also be difficult.

Honestly, this woman is AMAZING. Here's her website:
[http://www.suzanaherculanohouzel.com/lab](http://www.suzanaherculanohouzel.com/lab)

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buboard
Oddly we know a lot more about the electrophysiology of neurons of mice than
of humans. Compartmentalization of synaptic integration is known to have
computational consequences, e.g. see Bartlett Mel's work :
[http://www.pnas.org/content/111/1/498.short](http://www.pnas.org/content/111/1/498.short)

~~~
lamename
I don't find it odd, I don't plan to volunteer my living brain for patch clamp
experiments :)

~~~
ItsMe000001
Wouldn't one use two-photon microscopy? Patch clamp is quite limited in
comparison.

There also is the combination of both methods - not surprisingly, they write
how hard it is in a living brain (the clamping, the two-photon microscopy part
is much easier): [https://www.the-scientist.com/daily-news/robotic-patch-
clamp...](https://www.the-scientist.com/daily-news/robotic-patch-clamping-
gains-eyes-31008)

Here is an article describing "three dimensional two-photon brain imaging in
freely moving mice using a miniature fiber coupled microscope":
[https://www.nature.com/articles/s41598-018-26326-3](https://www.nature.com/articles/s41598-018-26326-3)
(the experiments that I was aware of all still were done on a sedated animal
with a fixated head).

~~~
buboard
when studying the propagation of dendritic signals, you would like to know the
subthreshold voltage response at the soma. Since no spikes are elicited there
is no calcium signal. Thats why you need patching.

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Kim_Bruning
There's quite a lot of fluff here, but I think the actual story is that some
MIT researchers have been using novel techniques to do electrophysiology on
dendrites?

Which is cool; I just wish the article had gone into more detail on that. (and
maybe included references :-) )

~~~
gumby
It’s not an article, it’s a press release from MIT’s publicity office full of
stuff reporters can pull out to write their own articles without attempting to
understand the paper.

The actual paper is here:
[https://www.cell.com/cell/pdf/S0092-8674(18)31106-1.pdf](https://www.cell.com/cell/pdf/S0092-8674\(18\)31106-1.pdf)

~~~
Kim_Bruning
thank you! :-)

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ivan_ah
Link to journal article:
[https://www.cell.com/cell/pdf/S0092-8674(18)31106-1.pdf](https://www.cell.com/cell/pdf/S0092-8674\(18\)31106-1.pdf)

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Nelkins
Would be interesting to see if genetically engineered rodents with similar
neuronal characteristics have improved intelligence (for some measure of
intelligence).

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hliyan
> electrical signals weaken more as they flow along human dendrites, resulting
> in a higher degree of electrical compartmentalization, meaning that small
> sections of dendrites can behave independently from the rest of the neuron

Reading this, I just realized that all this time I was using the wrong
computing analogy to understand the brain: neurons are not the transistors of
the brain, dendrites are!

~~~
teekert
To be honest, using a transistors analogy may keep you on the wrong path for a
long time as well :) There is not a lot of "digital" going on in those
cells...

~~~
JoeAltmaier
Wait - transistors are not digital they're analog. And neurons are terribly
digital, acting as rate controllers and pulse counters and dividers and so on.

~~~
achileas
That's oversimplified and usually how it's taught at the undergrad level.
Neurons and especially the networks they form are more analogous to analog
electronics, but both analogies end up failing at some point.

~~~
protonfish
From what I know, neurons typically click on or off, so they are digital in
that way. Signal strength is implied by the frequency of those clicks, so
that's analog. Transistors are analog electronics, but used to make digital
switches so it's sort of the reverse.

I guess my point is that calling neurons analog or digital is not a very good
analogy and should probably be avoided.

~~~
nickpsecurity
It's a mixed-signal, general-purpose ASIC done in wetware. Combines both
digital and analog traits. Some of most interesting research I saw in hardware
CompSci does the same. Never goes mainstream since industry prefers things
that are easy to automate and scale up for obvious reasons.

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hosh
I kinda wonder if neuro-atypical human neurons behave about the same or
differently -- for example, autism, ADHD, etc.

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anonymfus
How bad these news are for studies of human neurodegenerative deseases on
animal models?

~~~
achileas
Not really. Much of the research doesn't focus on the electrophysiology of
single neurons, but rather how networks are impaired and what causes the
impairment.

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maerek
Is it possible to strip the Facebook click ID from URLs submitted to Hacker
News?

The link for the story includes the following:
fbclid=IwAR2szOstJ6_hkoar2mo8NkXXMaOnfnIS5rFq5YNcOPf397n5HctnSUCGHjk#.W86CSfP5s-9.facebook

~~~
sctb
Thanks! We've added that to our list of strippy things (AMP is up next) and
removed it in this case.

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tmsldd
funny how neuroscientists use terms such as "computation" and "(more)
computing power", with no proper definition

~~~
arghwhat
Floating point operations, and more FLOPS.

Definitely.

