We resume our look at the neocortex, the seat of the mind, in more detail. Here's an image of a slice through part of a monkey brain. The nerve cells (neurons) have been stained in purple, and the neocortex is seen to the right, as a folded sheet of neurons. Since this is a slice the sheet looks more like a folded, concertinering, snake. You can see deep crevasses in the cortical mantle, which are deep infoldings of the sheet. Then underneath this thick purple layer of cells you can see a much paler underlayment - there are no neurons here, but enormous numbers of "wires", or "axons", which are carrying information too and from the overlying sheet of cells. Near the bottom, outlined with a dotted circle, you can see where the cortical sheet fizzles out, forming a curled much thinner but darker sheets called the hippocampus. This is where memories are, at least initially stored - but the memories here are not really complete, more like thumbnails which can trigger a more complete, cortically-based, version.
The sheet of cortical neurons is quite thick (1/3 inch) and is made up of 6 distinct layers. However, the detailed structure of these layers varies quite a bit from one patch of the cortical towel to another. Each patch of cortex seems to process different types of information. For example, the human visual cortex at the back of the head receives (indirectly, via the thalamus, which I will describe shortly) information from the eyes. It then sends this information to other cortical visual area for further processing. These areas are specialized for aspects of visual processing, such as movement or color.
In the center of the image about 1/3 of the way down you can see the visual thalamus, labelled LGd. It has also 6 layers of cells, with alternating layers receiving input from either the left or right eye. Near to the visual thalamus are other thalamic areas, for example labelled VPM,VPJ,LP. These relay other types of information to different patches of the cortex. For example, LP receives partly processed visual infrmation form the primary visual cortex, and sends it back to the cortex (eg to motion or color areas) for further processing.
So, the way the mind digests the world is rather like the way the alimentary canal digests our food: it's done in multiple steps (stomach, duodenum, small and large intestine. Somewhat different types of intellectual "enzymes" are applied at each step, with the net result being not crap but a (sometimes crappy) decision or thought.
What I really want to focus on is the mental digestion process that allows mere "data" (e.g. pixels, supplied by the eye) to lead to ideas. Let's specifically consider object recognition: our ability to glance at an object (e.g. a cup or a hand) and (usually) quickly and almost effortlessly decide what it is.
We are so good at this that it's easy to forget that it's almost a miracle. You can hook a camera up to a supercomputer, and show it a cup or hand, and, however artfully it's programmed, it cannot decide what it is! And it certainly cannot tell you that it's a hand holding a cup! At least now, in 2014. The problem is that while a cup is obvious to us, to a computer it's just a mess of pixels. For images of cups those pixels are different in a specific way from the pixels making up a hand, but this crucial difference ("cupness" versus "handiness") is extremely difficult to define, making it very difficult to program the computer.
Roughly speaking we think that the way the brain (and the cortex in particular) recognises this difference is by large amounts of experience: it has seen many versions of cups and many versions of hands, and it has learned to tell the difference (even without anyone ever saying "these are cups" and "these are hands"). These experiences each generate subtle changes in the connections between the relevant neurons (e.g in the various cortical visual areas mentioned above), such that as information is passed from one set of neurons to another, it's gradually transformed. In the original pixel-based version in the eye, there are no neurons which fire exclusively in response to cups or hands, but somewhere deep in the cortex (I mean, after many stages of cortical digestion) there are neurons that respond only to cups and others that respond only to hands (and others which respond to hands-holding-cups).
This not only works for relatively simple tasks like object reognition, but also, though more painstakingly, for more subtle things like deciding where to dine out tonight, how to purchases that delicious cake, who to marry and figuring out how the brain works.
At this point my reader might start to feel uncomfortable: am I saying that love, and science, and religion, is "nothing other" than the firing of certain neurons? And that furthermore these patterned firings are determined by a purely mechanical, automatic, digestion-like process involving changes in the numbers and strengths of neural connections? The soul boils down to "connectoplasm" (the sneering term used by Steven Pinker in his popular but weighty tome "How the Mind Works"?
In a nutshell I believe this is true, but that the truth is far more amazing than the alternatives, such as those proposed by Pinker or the Pope.....................