So how might resonant memory work? Here’s a highly simplified diagram:
There are two neurons here, creating a loop. How likely is this to happen with millions of nerve cells spreading dendrites all over the cortex?
To the extent that it does happen, it could set up a loop with a specific frequency:
The frequency (f) of this loop is approximately equal to the nerve impulse velocity (v) divided by the length of the loop (L). This doesn’t take into account the time added by each synapse, but it’s a rough start. Whatever the velocities of each axon and the lag of each synapse, this particular little loop has a cycle time associated with it. If you hit it with an input with a matching cycle time, this loop will resonate:
The input stream has pulses separated by t, the cycle time of the loop. The first pulse to hit will circle the loop and feed back into the starting neuron, just as the second pulse is coming in. Because the body of the neuron sums the inputs, it will keep sending a strong signal through the loop. The synapses are strengthened when a signal continues to impact them, so this circuit starts to provide stronger and stronger resonant signals as time goes on. We are training this loop to respond to the input.
The output is just the same as the input here, so we haven’t really accomplished much. But we have seen just how easy it is to create a hypothetical neural circuit that can resonate with a given input.
This site is a repository for information about a theory of memory that relies on resonant circuits.
First, the requisite metaphor:
Imagine a room full of thousands of tuning forks. They are all mounted by their handles, and the frequency of each fork is printed clearly on each mount.
A tuning fork on a resonance box. From brian0918 at en.wikipedia.
I give you a task: find the 440 Hz tuning fork that is somewhere in the room.
If you think like a computer, you will methodically search the room, looking at the printed frequency on each fork, checking for 440. They aren’t in any order, so your search is exhaustive: you can’t stop until you find the right fork. If there are a bunch of 440 forks and you need to find every one of them, then you will have to examine every single fork to be sure you don’t miss any.
But physicists and musicians know a faster way: Bring your own 440 fork and hit it. It will hum out a nice Concert A and as soon as it does, the other 440 forks in the room will immediately resonate with it. You can walk right over to the resonating fork, no searching required. If you have to search for multiple forks, no problem: they are all resonating sympathetically with each other.
If we consider each fork to be a piece of information or a bit of memory, we might find this to be a useful real-world analog for a new kind of computing. The resonance technique has some benefits:
- The information can be retrieved instantly
- The information is recalled by presenting an example of the information itself: the information is “content-addressable”.
- If the information doesn’t exist, you will know it instantly, because none of the existing information will resonate.
- Multiple pieces of information can be found as fast as a single piece of information.
Due to the above benefits, this style of “resonant memory” could be superior to current address-based memory. Furthermore, it may actually provide a plausible neural code for brains.