What is the goal of the nervous system, part 2 (a twitter story)

My question from Monday spawned some good discussion on twitter (none, alas, on the blog). What is the goal of the nervous system? Well, a lot of people thought it was pretty simple:

As evidence for how important movement is for having a brain:

Yup, when a sea squirt decides to stop moving it just sits there… and consumes its own brain (for some definitions of ‘brain’).  The video at the top, as suggested by Chris Maidan, is a great explanation of the reasoning behind the idea that the brain is for movement. Yet, despite Daniel Wolpert explicitly saying that the reason we have a brain is for movement… he actually makes an argument for something else that came up in the twitter discussion:

Another good alternative:

And to throw in a curveball:

But the answer that I like the best:

I have some thoughts that I’m writing up, though that is taking some time. Let me take a step back, though, and reword what my question was originally intended to be (though clearly in my sleep-deprived state I did a poor job of describing it).

As others suggested above, the overall goal of any part of a biological system is to maximize the transmission of genetic material (by one mechanism or another) from one generation to the next. Yet when examining the nervous system on a more local level that can be hard to notice; the visual system, especially the early stages, are there to extract information about visual scenes; the auditory system is there to extract information about sound; the spinal chord is there to (mostly) generate movement. If you don’t believe me, look at the peripheral sensory nerves, at the retina, at the cochlea: all part of the nervous system, and on a local level they are guided by local goals. It is not until you get to more internal structures that general ideas of value or desire are found.

And we can write this out mathematically; sensory neurons are often said to be maximizing the Shannon mutual information between their response and the visual world which we can write in a very simple way I(neural response;visual stimulus) with plenty of experimental support. In other words, the visual neurons represent as much information about the visual scene as is possible.

But given that we know that the ultimate goal of the nervous system is to enhance reproductive success – why isn’t that included in the equation? Where would we need to include something like that to have a good understanding of the function of some area of the visual system? Is a proxy like ‘utility’ good enough?

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One thought on “What is the goal of the nervous system, part 2 (a twitter story)

  1. Pingback: Monday thought/open question: What is the goal of the nervous system? (Updated) | neuroecology

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