In my most recent post I gave an overview of the "simple recurrent network" (SRN), but I'd like to take a step back and talk about neuromodeling in general. In particular I'd like to talk about why neuromodeling is going to be instrumental in bringing about the cognitive revolution in neuroscience.
A principal goal of cognitive neuroscience should be to explain how cognitive phenomena arise from the underlying neural systems. How do the neurons and their connections result in interesting patterns of thought? Or to take a step up, how might columns, or nuclei, interact to result in problem solving skills, thought or consciousness?
If a cognitive neuroscientist believes they know how a neural system gives rise to a behavior, they should be able to construct a model to demonstrate how this is the case.
That, in brief, is the answer.
But what makes a good model? I'll partially answer this question below, but in future posts I'll bring up specific examples of models, some good, some poor.
First, any "model" is a simplification of the reality. If the model is too simple, it won't be interesting. If it's too realistic, it will be too complex to understand. Thus, a good model is at that sweet spot where it's as simple as possible but no simpler.
Second, a model whose ingredients spell out the result you're looking for won't be interesting. Instead, the results should emerge from the combination of the model's resources, constraints and experience.
Third, a model with too many "free" parameters is less likely to be interesting. So an important requirement is that the "constraints" should be realistic, mimicking the constraints of the real system that is being modeled.
A common question I have gotten is: "Isn't a model just a way to fit inputs to outputs? Couldn't it just be replaced with a curve fitter or a regression?" Well, perhaps the answer should be yes IF you consider a human being to just be a curve fitting device. A human obtains inputs and generates outputs. So if you wish to say that a model is just a curve fitter, I will say that a human is, too.
What's interesting about neural systems, whether real or simulated, is the emergence of complex function from seemingly "simple" parts.
In future posts, I'll talk more about "constraints" by giving concrete examples. In the meantime, feel free to bring up any questions you have about the computational modeling of cognition.
[Image by Santiago Ramon y Cajal, 1914.]