Dick Pountain/17 November 2008 12:54/Idealog 172
You might not believe it but I actually plan these columns rather than just spout off the top of my head. I keep a list of topics and notes in Bonsai, assigned to issues via names like Idealog 172 and so on. At the bottom, unassigned, are tricky-but-important topics I keep chickening out from, and topping that list is "Body As Computer". I mean by that an essay on how the human body contains at least six distinct information processing systems, networked together using a variety of different transport fabrics.
It's no longer controversial to describe the human brain as an organic computer, though it's plain wrong to imagine that it works much like a digital computer. One of its jobs is to sample your surroundings, using five main information channels - sight, sound, touch, smell and taste - in order to alert you to dangers and opportunities, communicate with other humans and simply to enjoy the view. Your brain doesn't store this raw sample data whole the way a PC stores bitmaps and MP3s, but first analyses it into more primitive units: say lines, edges and curves in the case of visual data. Memories are stored in some very, very compressed format that employs these primitives, and which remains yet to be elucidated. To remember is actually to reconstruct from such a compressed description (not always entirely accurately).
Brains evolved over several million years but at each major evolutionary "upgrade" backward compatibility had to be maintained just to keep breathing (not so unlike the IBM-compatible PC then). As a result the human brain contains at least three co-processors of different evolutionary ages, wrapped around one another like layers of an onion. The core is the oldest, the brainstem we share with all vertebrates including reptiles and fishes, an efficient control processor that keeps us alive by regulating crucial physiological processes like heart rate, breathing, blood gases and electrolytes. It also controls basic fight-and-flight response: if the "red mist" of rage descends, that's your brainstem talking. Wrapped around this is an emotional co-processor called the limbic system that we share with other mammals: this adds higher-level social skills like caring and playing, needed to cope with living in social groups and extended child rearing. It's wired to other parts of the brain by sheets of neurons, but also talks to the rest of the body by secreting hormones into the blood stream, and neurotransmitters into the cerebral fluid that modify the operation of the other two co-processors. The newest, outermost layer, the cerebral cortex handles reasoning, speech, planning and all the specifically human stuff we do: our cortex is much bigger than any other primate's.
Your DNA is another information processing system, a huge database that specifies not just how to make all your body parts, but various aspects of running them too. Bodily actions are driven by chemical reactions catalysed by enzymes, which are proteins created by copying their blueprint from a gene imprinted on a strand of DNA. Each cell in your body contains a full copy of your genome with most of its genes turned off (otherwise it would be churning out every possible enzyme all the time). Selectively turning genes on and off controls the activity of individual cells and these vastly complicated control loops form a whole other level of computation, which interfaces with the three brain processors because they're made of cells and so everything they do is controlled by gene expression.
Then there's the immune system, an extraordinarily efficient error correction system that monitors your body for rogue processes. With so many cells expressing different genes, a few are bound to go haywire all the time but the immune system spots their unwanted proteins and shuts them down. Ditto against foreign nasties like bacteria and viruses that invade you from the outside. Your immune system heads off threats millions of times a day and you fall ill on the rare occasions when it fails - in much the same way that you can hear a glitch on a CD if the error correction code fails to cope with a gap, but you don't hear the thousands of errors it does fix every second. How the immune system interacts with mental processing will one day be the hottest topic in medicine (think placebo effect).
Metabolic control now appears to be yet another information processing system, distributed between brain, stomach, liver, colon, muscles and skeleton. Fat cells hold two-way conversations with bones, and both with brain, employing a bewildering range of newly-discovered hormones like leptin, ghrelin, cholecystokinin, adiponectin and osteocalcin. A small brain region, the arcuate nucleus of the hypothalamus, integrates all these queries (how heavy?, how full?, what blood glucose level?, how much fat on deposit?) to calculate how hungry you should feel. Unravelling the workings of this system will one day lead to novel treatments for obesity, diabetes and a variety of related ailments. And it's likely that several more chunks of your anatomy currently believed to be merely structural will turn out to be information-processors too, networked to these six to keep you ticking. Fascinating stuff, one day I really must write it all up...
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