Brains & Machines

From a traditional scientific perspective, and from a basic common sense point of view, most of us assume that the world we live in is one which we see,  hear, touch, taste, and smell.   That the environment we perceive around us is the result of our senses telling us the make up of an objective and separate reality.  Certain findings, however, conflict with that very fundamental notion.  Recent anatomical studies of cortical connectivity tell us something very different, namely, that the input to our brains from sensory organs is actually quite sparse.  Rather than synaptic input from sensory organs, the vast majority of connections are interneurons (i.e. neurons talking to other neurons).  For the visual system, only about 5-10% o f synapses are connected to the periphery, whereas the majority of neuronal interactions are reflecting intrinsic or thalamocortical connections.  When you run the numbers (as one of my graduate students did), the brain consists of approximately 10¹² neurons (1 with twelve zeros after it), each making a synaptic contact 5,000 to 10,000 times. That makes for a total of  10¹⁶ synapses – a very large number indeed.   Now in thinking about information coming in, the retina has about 1,000,000 fibers going into the brain. Again assuming 5,000 to 10,000 synaptic connections that brings  us to about 10¹⁰ synapses.  Taken together, that means there are a million times more connections in the brain than there are for the actual input and processing of vision.  The same holds true for the output side of things.  When considering the cortiospinal tract,  the pathway of all the motor axons that execute every movement we are capable of, again we see a number of about 10⁶ fibers.  Again, much much lower than the total number of connections in the brain.

            So what’s the brain doing?  It would seem the preponderance of brain activity and communication is not in the moment to moment processing of sensory inputs coming from the outside world, nor is it occupied with external behavior either. So again, what gives?   There are a growing number of scientists who think the brain is in the business of predicting the world around it, rather than actively processing the activity as its coming in.  To predict upcoming events you have to have a “model” to compare against.  Maybe another word for a model, is a pattern of expected experiences or behaviors.  So rather than sensing the world around us, our brains create a model of what the world should be and use our senses to tell us whether our model is correct or not.  From an evolutionary standpoint, being able to predict events – like when I see a shaking of the bushes there will be a tiger there – helps us survive.  Its also more energy efficient.  Our brains are not busy rebuilding the world on a moment by moment basis, we have a model of what that world is and we check every so often to make sure its correct.  If not, then we’ll make changes to the model.

            I think what is fundamentally interesting about this proposition is the important role the “observer” plays in their environment.  Because it really isn’t our environment that we perceive, its our model of that environment.  So we are all really walking around in the world we created for ourselves.  Thus, when we are depressed the world is indeed a darker place, and when we are happy the world is brighter.  To push this a little further, I think that we can alter and change that model, and thus we can in a certain sense impact the world we live in.  So for the cynic, who thinks nothing good come out of anything – they’re right.  But the limitation is not that the world is a shitty place, it’s the barriers in their own mind.