Comment Info depends on the config of neuron/ 500 Mb max? (Score 1) 82
Interesting things said in this 'ask slashdot'
I'm a very little bit of an expert, as I am very specialized in only one little region of the brain. So this is just my $.02 ! With this in mind, I'd like to make a few remarks:
1. As others pointed out, the question is confusing. A nerve is a bundle of neuronal processes, mostly axons. Depending on the nerve, the type and amount of axons varies. So a nerve is too complicated to start guessing about bandwith. Let's assume the question regards axons 'stead nerves.
2. Even axons form a complicated model. One axon may (but not always does!) bifurcate hugely! In the brain, one neuron (BTW: thusfar no neurons with more than one axon have been observed) contacts on average one thousand (1E3) of other neurons. I don't know about the maximum contacts observed. To simplify, assume one neuron, one axon, one contact.
3. Information along an axon travels on action potentials. As others have pointed out nicely, the maximum frequency cannot exceed the 500 Hz. But although every action-potential is identical at the axon, the reaction it elicits may vary enormously. Action potentials act via chemical messangers, and each messanger acts via it's own pathway. Different messangers from the same neuron may interact, and the history (short-term, long-term) of each messanger, each pathway, each integration step may be of importance. Again, let's simplify. Consider an axon with one synaptic contact on one target neuron acting on that neuron via one pathway that is static, so the pathway's characteristics don't change at all in time. You probably can't find such an axon, and if you find it, you'll have a very very hard time to proof it's indeed that simple. But, let's assume we are looking at this marvle right now.
4. In order to grasp the bandwith, we need the bus-width, as we already know the maximum frequency. So how much information does one single action potential encode maximally? The answer is, we just don't know. Consider the visual system. Receptors in the retina catch light. Depending on the receptor, it's state and the wavelength of the photon, one or more photons may be required. (BTW: these receptors do not encode with action potentials) So, the receptors reaction may encode the place of the impact, more or less the intensity of the impact, and partly the color of the impact. We don't know the resolution of the eye, but let's assume it's 8 times as high as our screen. So 8x1200x8x1000= is somewhat like 80e6, 27 bits. Truecolor=32 bits (;-)), you need three types of receptors for that, so 11 bits. That's 38 bits only at the beginning of the cascade. The information is processed at a lot of levels, from detection of light spots, lines, squares, circles until the detection of objects and their relative speed etc. How many bits is the message there is a dangerous object, so -and so large, this form, this speed, that color etc. in the upper right corner of your eye (BTW: i don't know if such a neuron/message exists, but it could be possible)? One megabit? And where does it stop? No-one knows (Daniel Dennett, consiousness explained, argues it never stops, but somewhere along the pathway a reaction is triggered, and a thought occurs (more denett: a thought thinks you)). Maybe I could imagine a action potential of one gigabit? Let's cut it somewhere. One megabit. That makes our simple model a bandwith of 500 Mbit maximum. Or 500 kbit, give or take a factor thousand.
5. At billions and billions of neurons residing in your brain, you make a pretty speedy connection!
Enough mindgames for now...
Cheers,
Jeroen
I'm a very little bit of an expert, as I am very specialized in only one little region of the brain. So this is just my $.02 ! With this in mind, I'd like to make a few remarks:
1. As others pointed out, the question is confusing. A nerve is a bundle of neuronal processes, mostly axons. Depending on the nerve, the type and amount of axons varies. So a nerve is too complicated to start guessing about bandwith. Let's assume the question regards axons 'stead nerves.
2. Even axons form a complicated model. One axon may (but not always does!) bifurcate hugely! In the brain, one neuron (BTW: thusfar no neurons with more than one axon have been observed) contacts on average one thousand (1E3) of other neurons. I don't know about the maximum contacts observed. To simplify, assume one neuron, one axon, one contact.
3. Information along an axon travels on action potentials. As others have pointed out nicely, the maximum frequency cannot exceed the 500 Hz. But although every action-potential is identical at the axon, the reaction it elicits may vary enormously. Action potentials act via chemical messangers, and each messanger acts via it's own pathway. Different messangers from the same neuron may interact, and the history (short-term, long-term) of each messanger, each pathway, each integration step may be of importance. Again, let's simplify. Consider an axon with one synaptic contact on one target neuron acting on that neuron via one pathway that is static, so the pathway's characteristics don't change at all in time. You probably can't find such an axon, and if you find it, you'll have a very very hard time to proof it's indeed that simple. But, let's assume we are looking at this marvle right now.
4. In order to grasp the bandwith, we need the bus-width, as we already know the maximum frequency. So how much information does one single action potential encode maximally? The answer is, we just don't know. Consider the visual system. Receptors in the retina catch light. Depending on the receptor, it's state and the wavelength of the photon, one or more photons may be required. (BTW: these receptors do not encode with action potentials) So, the receptors reaction may encode the place of the impact, more or less the intensity of the impact, and partly the color of the impact. We don't know the resolution of the eye, but let's assume it's 8 times as high as our screen. So 8x1200x8x1000= is somewhat like 80e6, 27 bits. Truecolor=32 bits (;-)), you need three types of receptors for that, so 11 bits. That's 38 bits only at the beginning of the cascade. The information is processed at a lot of levels, from detection of light spots, lines, squares, circles until the detection of objects and their relative speed etc. How many bits is the message there is a dangerous object, so -and so large, this form, this speed, that color etc. in the upper right corner of your eye (BTW: i don't know if such a neuron/message exists, but it could be possible)? One megabit? And where does it stop? No-one knows (Daniel Dennett, consiousness explained, argues it never stops, but somewhere along the pathway a reaction is triggered, and a thought occurs (more denett: a thought thinks you)). Maybe I could imagine a action potential of one gigabit? Let's cut it somewhere. One megabit. That makes our simple model a bandwith of 500 Mbit maximum. Or 500 kbit, give or take a factor thousand.
5. At billions and billions of neurons residing in your brain, you make a pretty speedy connection!
Enough mindgames for now...
Cheers,
Jeroen
