Idealog

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 such as 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, although it’s 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 physiological processes such as heart rate, breathing, blood gases and electrolytes. It also controls basic fight-or-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, which we share with other mammals: this adds higher-level social skills such as caring and playing, needed to cope with living in social groups and extended child-rearing. The newest, outermost layer, the cerebral cortex, handles reasoning, speech, planning and all the human stuff we do: our cortex is much bigger than that of any other primate.

Your DNA is another information-processing system, a database that specifies not just how to make 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 that 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 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 such as 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 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 fixes every second. How the immune system interacts with mental processing will one day be the hottest topic in medicine (think placebo effect).