The hippocampus as a 'predictive map' • Hacker News Board

Re: The hippocampus as a 'predictive map'

#31

Post by eru » Tue, Oct 03, 2017, 2:13 PM UTC

mannigfaltig wrote: post #28

eru wrote: post #18

Earlier quoted context omitted.

Current AI approaches don't have that much to do with the biological brain. Despite the name 'neuronal networks' that we have history to thank for, it's better think of them as just long compositions of functions with a lot of parameters one can tweak. Historically researchers looked at activation functions that are at least somewhat justified by nature, like the sigmoid. More recently people have focused on the math…

> Despite the name 'neuronal networks' that we have history to thank for, it's better think of them as just long compositions of functions with a lot of parameters one can tweak. Actually, the name is not so misleading because `ReLU(Wx + b)` is an approximation of the response of a large ensemble of integrate-and-fire neurons in terms of the firing rate [1] (it models populations of pyramidal neurons in the cortex).…

Thanks! Yes, you can find that the ReLU does model some aspects---but if memory serves right people didn't switch from sigmoid to ReLU because they were interested in modelling the brain better, but mostly because they were looking for a structure that's simpler to train. Sigmoids notoriously smear out all your backpropagation 'juice' after only a few layers, don't they?

(I only mention ReLU because they are definitely simpler in mathematical structure than ye olde sigmoid. Max out is another interesting activation function that's first and foremost inspired by the math / pragmatics of drop-out training, and were any relations to biology more likely to be subsequent discoveries and not intentional design features.)

Re: The hippocampus as a 'predictive map'

#32

Post by zardo » Tue, Oct 03, 2017, 2:20 PM UTC

eru wrote: post #29

orbifold wrote: post #23

Earlier quoted context omitted.

Actually ReLU(x) = max(x,0) can be thought after a change of parameters as the firing rate response of a leaky integrate and fire neuron at least for a certain range of parameters. So it is not completely far fetched, but of course nature does not use rate coding exclusively.

Yes. Though I think they stumbled on ReLU just from technical considerations and not taking nature into account? That happens fairly often in engineering: looking around enough one can often find natural precedents for our artifices. But directly trying to copy nature did not lead to the plane or helicopter.

Wikipedia list this as the first paper involving ReLU in an ANN:

[1] R Hahnloser, R. Sarpeshkar, M A Mahowald, R. J. Douglas, H.S. Seung (2000). Digital selection and analogue amplification coexist in a cortex-inspired silicon circuit.

Re: The hippocampus as a 'predictive map'

#33

Post by SubiculumCode » Tue, Oct 03, 2017, 2:34 PM UTC

dontreact wrote: post #7

I don't know how this theory fits in with patient H.M. who was still capable of many types of learning and planning, despite having his entire hippocampus removed. https://en.wikipedia.org/wiki/Henry_Molaison At the least such a broad sweeping theory of how a brain region works should address how it fits in with evidence with the most famous lesion (and deeply studied) patient who did not have said brain area?

As much as I love the hippocampus (topic of my dissertation), I had to constantly remind myself that there is a lot of other brain.

Re: The hippocampus as a 'predictive map'

#34

Post by gnaritas » Tue, Oct 03, 2017, 2:54 PM UTC

dwringer wrote: post #24

_0ffh wrote: post #14

Earlier quoted context omitted.

I didn't downvote, but I have an inkling. I'll share what some of these people may be thinking about your comment. I'll be hyper-critical there because you specifically asked about why someone might have downvoted, so don't take it personally. "Reading about rewards in AI context makes me wonder, why current AI only focuses on the network topology aspect of natural intelligence." Well, it doesn't. Not at all. It look…

If someone only has familiarity with AI from reading passing news stories, it is reasonable to think they would have such a perception of the field. I think your diagnosis of the downvoters might be correct, but "not even wrong" seems a bit extreme. AFAIK somebody out there is probably trying to do a research paper on simulated neurotransmitters as we speak. More interesting would be if anyone had links to existing r…

> it is reasonable to think they would have such a perception of the field.

It really isn't; what's reasonable is to always assume whatever you thought of in 10 seconds, has been deeply researched regardless of whether you're aware of it or not. What's reasonable is to assume researchers are vast leagues ahead of whatever shallow thoughts you have on a subject since you "know" you have a shallow understanding. The reasonable person simply asks for links to read deeper about a subject, they don't criticize something they have a shallow understanding of and ask why no one is doing X.

Re: The hippocampus as a 'predictive map'

#35

Post by SubiculumCode » Tue, Oct 03, 2017, 2:59 PM UTC

itschekkers wrote: post #27

rayuela wrote: post #21

Just $225 to read the actual paper... what a steal! If someone would so kindly share that pdf on here I'd greatly appreciate it. Nvm found it: https://www.biorxiv.org/content/early/2016/12/28/097170

theres a website called sci-hub (which maybe illegal) that you can use to get almost any paper in a STEM field, especially from major journals. you type www.sci-hub.cc/ and then paste the DOI of the paper. it takes you straight to the pdf!

Or you can contact the researcher, who are generally happy to share our research via email. Or check their researchgate.

Re: The hippocampus as a 'predictive map'

#36

Post by duozerk » Tue, Oct 03, 2017, 3:00 PM UTC

itschekkers wrote: post #27

rayuela wrote: post #21

Just $225 to read the actual paper... what a steal! If someone would so kindly share that pdf on here I'd greatly appreciate it. Nvm found it: https://www.biorxiv.org/content/early/2016/12/28/097170

theres a website called sci-hub (which maybe illegal) that you can use to get almost any paper in a STEM field, especially from major journals. you type www.sci-hub.cc/ and then paste the DOI of the paper. it takes you straight to the pdf!

Also if it doesn't work (happens from time to time) or disappears, they have a tor mirror that works consistently: scihub22266oqcxt.onion.

Re: The hippocampus as a 'predictive map'

#37

Post by [deleted] » Tue, Oct 03, 2017, 3:06 PM UTC

gnaritas wrote: post #34

dwringer wrote: post #24

Earlier quoted context omitted.

If someone only has familiarity with AI from reading passing news stories, it is reasonable to think they would have such a perception of the field. I think your diagnosis of the downvoters might be correct, but "not even wrong" seems a bit extreme. AFAIK somebody out there is probably trying to do a research paper on simulated neurotransmitters as we speak. More interesting would be if anyone had links to existing r…

> it is reasonable to think they would have such a perception of the field. It really isn't; what's reasonable is to always assume whatever you thought of in 10 seconds, has been deeply researched regardless of whether you're aware of it or not. What's reasonable is to assume researchers are vast leagues ahead of whatever shallow thoughts you have on a subject since you "know" you have a shallow understanding. The re…

[deleted]

Re: The hippocampus as a 'predictive map'

#38

Post by [deleted] » Tue, Oct 03, 2017, 3:13 PM UTC

gnaritas wrote: post #34

dwringer wrote: post #24

Earlier quoted context omitted.

If someone only has familiarity with AI from reading passing news stories, it is reasonable to think they would have such a perception of the field. I think your diagnosis of the downvoters might be correct, but "not even wrong" seems a bit extreme. AFAIK somebody out there is probably trying to do a research paper on simulated neurotransmitters as we speak. More interesting would be if anyone had links to existing r…

> it is reasonable to think they would have such a perception of the field. It really isn't; what's reasonable is to always assume whatever you thought of in 10 seconds, has been deeply researched regardless of whether you're aware of it or not. What's reasonable is to assume researchers are vast leagues ahead of whatever shallow thoughts you have on a subject since you "know" you have a shallow understanding. The re…

[deleted]

Re: The hippocampus as a 'predictive map'

#39

Post by kortex » Tue, Oct 03, 2017, 3:17 PM UTC

mh-cx wrote: post #10

Reading about rewards in AI context makes me wonder, why current AI only focuses on the network topology aspect of natural intelligence. What about the neurotransmitters like dopamine or serotonine? Could they (or more specific: their effects) be key to an AI that feels more “natural“?

Glutamate is the primary "connection" neurotransmitter in the brain ("It is used by every major excitatory function in the vertebrate brain, accounting in total for well over 90% of the synaptic connections in the human brain."). DA and SER are far more sparse and unevenly distributed, concentrating in areas with heavy interconnectivity, such as the limbic system and hippocampus. These monoamines are thought to primarily serve in a modulatory role, affecting performance and stability of neural connections in general, in an on-line fashion.

By comparison, ANNs have many meta-parameters (parameters besides the actual weights), such as learning rate and momentum, affecting stability and performance. Being able to tune these on the fly would likely improve performance.

The "ANNs are not like the brain!" camp like to point out that the ANN is a mathematical model bearing (on one level) little similarity to the human brain, but I think this glosses over the fact that key features (e.g. layers of connections, CNNs) were directly biologically inspired, and we can still glean a lot by studying the best example in our world of a learning system.

Re: The hippocampus as a 'predictive map'

#40

Post by chiggins » Tue, Oct 03, 2017, 3:20 PM UTC

pizza wrote: post #13

mh-cx wrote: post #11

Earlier quoted context omitted.

Downvoters please explain what's so stupid about my question.

I upvoted you, and I'm actually glad you asked the question despite downvotes. I imagine those who did are of the opinion that essentially you're ascribing too much function to the neurotransmitters themselves, as opposed to the contexts in which the presence of the neurotransmitters are used as signals. Take a look at this brain schematic here [0]. I vehemently disagree with some of the presented-as-fact ideological…

Not to derail this further, but your description of Parkinson's disease is incorrect. Dopamine plays a role, but it isn't degeneration motor neurons themselves. There are many effects, but the primary symptoms WRT motor control are caused by death of dopaminergic neurons whose cell bodies reside in the substantia nigra but innervate and regulate firing of corticostriatal pre-motor pathways.

[0] I did my PhD on this

[1] https://en.wikipedia.org/wiki/Parkinson%27s_disease#Pathophy...

[2] https://en.wikipedia.org/wiki/Nigrostriatal_pathway