Izawwlgood wrote:This is why I kept disagreeing with you; you don't need NT for signal propagation along an axon, but you do need NT to transfer signal to the next neuron. Post synaptic activity is entirely predicated on NT release and uptake by the next neuron in the circuit. You keep talking about ways to model/replace individual neurons, forgetting that signal propagation down an axon is pointless if you can't induce a synaptic bulb to release NT onto the next neuron; saying 'microfluidics will deliver small amounts of NT' forgets that neurons have a lifespan of... a lifespan. How do you propose replacing a lifetimes worth of neurotransmitter?
If you stick one electrode in the presynaptic neuron, one in the postsynaptic neuron, assuming you understand the normal dynamics of that kind of synapse (true for some NT, not for others), you can cut the axon, and use a microcontroller to shape pulses sent to the post-synaptic cell depending on the potential of the pre-synaptic one.
How much serotonin does your brain produce every year? I have no idea, but I suppose it is not on the order of liters. Remember it's a very potent neurohormone, you don't need a lot of it. Let's say a container of 10ml lasts for 5 years (no idea what the real figure is, even the order of magnitude), you would need an operation to "refuel" from time to time. It's not ideal, I agree, but early pacemakers had the same kind of issue, and it's much easier than growing an axon from the midbrain to both the cerebellum and the frontal cortex.
Izawwlgood wrote:To put it simply, just assume a spherical cow
You can't predict anything useful with spherical cows in a perfect vacuum, except maybe orbits. Electrical models of the neurons work, make predictions, and are used by everyone that is not studying a single molecule.
Angua wrote:How are you going to get the current to the cells your chip is going to be interacting with at a fine-tuned enough level not to damage the nerve (you're definitely going to need a way to make sure that it can detect what the target nerves are telling it so it knows when they've had enough). The ion currents are also not the only things the NT receptors affect - you're ignoring all the modulation of NTs that happens within the synapse (eg the cells will up/down regulate NT receptors depending on how often they are activated, other signalling pathways that can be activated (or inactivated) by NT receptor activation, the effects of the glial cells in modulating the NT transmission within the synapse, etc).
Electrical stimulation of single neurons, or small groups of neurons, is currently used. In humans. For years.
If you know the dynamics of NT receptor self regulation, you can emulate it by modulating your pulses.
And I already said currents can't emulate all that is not directly affecting the potential of the cell. Obviously, we can't replicate the effect of dopamine or serotonine with electrodes, and that's why I suggest microfluidics.
I'm not saying my solution is easy or perfect, just that it is much simpler than growing new neurons. Neurostimulation has been applied since what, the 60's? with very crude effects that have been refined to the point people are actually considering replacing the hippocampus.
Growing neurons, on the other hand, is something we have no idea how to do. And when we figure that out, we will have to figure out how to direct the growth of the axon, make it split, direct the growth of branches, same thing with the dendrites, all that through a fully grown brain, tightly packed with axons and other stuff, with similar neurons that will have NOT to be disturbed too much by the process.
Repairing the brain will consist largerly in rewiring stuff. A biological process is stochastic, and it is difficult to direct it without direct mechanical intervention.
The brain is not the skin, it's not renewing itself on a continuous basis, and there is no reason to believe it has mechanism to repair eveything magically if we drop stem cells in the right place. We aren't able to repair organs with a much simpler structure, and far less different types of cells. The day we are able to grow a liver or a pancreas from stem cells, with arteries and all, without using organ scafolds and such; this day only, biological solutions will have a chance to compete with engineered systems.