Does the brain really function like a computer as in, ultimately every response is related to a binary sequence based on whether particular neurons fire or not?
First of all, I would like to point out that making analogy between digital computers and the brain is often very misleading.
That being said, my answer is, some scientists believe so, some don't.
Several things to consider:
Some neural systems are not spiking. C. elegans for example has a nervous system that is entirely analogue. Human nervous system also contains neurons with graded responses (mostly in the sensory front-end though).
Spiking neurons may be binary at each time point, but time itself is continuous. Firing at 0.003 seconds later can represent something different. (in contrast to the usual synchronous digital architecture of computers)
The neuron doctrine is sometimes challenged. Glial cells that do not fire may have important functions for information processing. See:
- Bullock, T. H., Bennett, M. V. L., Johnston, D., Josephson, R., Marder, E., and Fields, R. D. (2005). The neuron doctrine, redux. Science, 310(5749):791-793.
1$\begingroup$ That's exactly what I was wondering; if in fact, some brain signals are propagated on a grade. Thanks! $\endgroup$ Feb 18, 2015 at 21:19
$\begingroup$ Plus neurons have modulators that change the way they behave. Some modulators may cause hyperpolarization while others may decrease the threshold for depolarization. $\endgroup$– One FaceFeb 18, 2015 at 23:17
While action potentials are usually binary, you should note that synaptic communication between neurons is generally not binary. Most synapses work by neurotransmittors, and this is a chemically mediated graded response that, for example, act on voltage-gated ion channels. So even though action potentials are often binary, communication between neurons are most often not, and action potential firing can involve the integration of synaptic information from many different neurons. Therefore, the brain as a whole cannot be reduced to a binary system.
See this as a complement to @Memmings answer.
1$\begingroup$ Many neurotransmitters (also) have metabolic G-protein-coupled receptors as their target. E.g. Glu has NMDA-receptors (Na,Ca-channels) and AMPA receptors (Na ion channel), but also a gamut of metabolic GLuRs as target. I slightly adapted your answer by adding 'e.g.' Fine answer. +1, therefore removed the intro line - unnecessary :) $\endgroup$– AliceD ♦Feb 20, 2015 at 13:09
$\begingroup$ Very interesting. Thanks for the response. I am not familiar with voltage-gated ion channels and will definitely be reading up on them. Thank you! $\endgroup$ Feb 20, 2015 at 17:00
John vonNeumann, the famous computer scientist, tackled this idea in his last book, 'The Computer and the Brain.' He personally landed on the side of the brain being a binary system, due to the behavior of neurons which either fire or do not fire.
While that is an important observation, and will have significant consequences to people trying to create artificial brains within computer systems, I think a more important observation has to do with computational complexity. It is very easy to build systems which, at least theoretically, have the potential to be universal computers. From that fact, it is fairly trivial to see that whatever definitions you choose to work with in terms of brain input and output (sensory nerve cells feeding electrical impulses from organs of perception being a possible definition of 'input' and propagated impulses to muscles, or changes in the neural structure itself being possible definitions of 'output' for example), yes it is possible to construct a binary system which can perform the same calculations as a human brain.
However, there is a catch. Because it is impossible to perfectly know the complete state of the brain, and because any degree of inaccuracy in the starting state of the binary system, no matter how small, will cause the behavior of the binary system to diverge completely from the behavior of the specific brain being modelled, it is reasonable to say that no particular individual brain can be reduced to a binary system.
as far as I know the brain processes data in stages the neurons themselves are not purely binary as in a computer in that every action has a predetermined output. the neuron response tends to be goverened by sigmoid function output and hence the use of this function in artificial neural networks. further, the synapses have strengths that is depended on the amount of neurotransmitter in there which obviously varies from cell to cell and even in the same cell and hence one speaks of the probability of a neuron firing given a certain stimulus. additionally the neurons from sensory organs fire pulses at a frequency that increases with the strength of the stimulus. furthermore, the data from sensors is processed in layers of neurons lower layers have rapidly firing neurons whule higher layers fire at much lower rates.
you also have to consider the fact that the brain is actually a complicated network of "recurrent" neurons meaning that the output is fedback as an input and this is different from simple computer gates such as AND gates or XOR gates it is similar to counters may be but obviously on a very bigger scale. one more point is that recurrent neural networks have built in memory that enables the pattern recall and recognition and so the study of the brain as a binary system is very complicated and will fail to explain how the brain works.
on the macro scale the human brain operates as a bayesian inference engine more or less I mean when it comes to thinking and inference i.e. it relies on probabilities and knowledge gained from past experiences to deal with current problems and new data
It's theoretically possible, because all information can be well approximated/copied in binary, and it's practically impossible because of size, energy, and program size/depth.
A fly brain is <1mm wide and an intel fly brain equivalent is >1000mm wide... much slower than the fruit fly. (Thats why flies see your hand coming in slow-mo).
This intel chip has as many neurons as a slug, far less than a fly: https://www.cnet.com/google-amp/news/intel-packs-8-million-digital-neurons-onto-brain-like-pohoiki-beach-computer-loihi-chips/
he binary model has to include "chemical modelling" and "physical modelling" like a graphics card which models light and creatures as binary.
Except that there is an added issue: processing speed. The brain can grow direct connections which are very fast. Silicon signals have to travel 1000 times further for every calculation.
2d chips take as much space as a skyscraper and a small nuclear station for energy, and future mythical 3d transistors would take space and would be slower because they require direct chemical processing and flexible internal connection to be as fast.
AI is very performant and is one of the future paradigm changes like "internet/mobile phone / electric car / AI "
human brain is strictly digital device using defined action potentials (0 volt as logical 0 and specified (fixed) voltage potential as logical 1). these two potentials work same way as complex logic gates systems. brain processes all types of analog-like variations (signal amplitude or response strength) as very short time based sums of logic gates operations. there is no other applicable description of brain functionality
2$\begingroup$ Welcome to Biology.SE! This seems to conflict with the accepted answer and could easily be mistaken for an opinion rather than an answer based on facts. Consequently, I think will find that supplying supporting references (primary literature is best) will help your answer receive a more favorable response. ——— You may also wish to take the tour and then consult the help pages on the standards for additional advice on How to Answer effectively. Thanks! 😊 $\endgroup$– tyersomeSep 1, 2019 at 0:33