"Do you know the half-life of a microtubule, the protein filaments that form the internal scaffolding a cell? Just ten minutes. That's an average of ten minutes between assembly and destruction.Yeah, that's what I want to know.
Now the brain is supposed to be some sort of computer. It is an intricate network of some 1,000 trillion synaptic connections, each of these synapses having been lovingly crafted by experience to have a particular shape, a particular neurochemistry. It is of course the information represented at these junctions that makes us who we are. But how the heck do these synapses retain a stable identity when the chemistry of cells is almost on the boil, with large molecules falling apart nearly as soon as they are made?"
Myelin and RNA molecules seem to last months. And DNA is of course fairly hardy, though it still needs continual repair. But on the kinds of figures that are coming out now, it seems like the whole brain must get recycled about every other month. And certainly everything points to the synapses as being about the most dynamic part of the whole system.Oh, that explains it. Sort of. Maybe.
Clearly the shape of the synapses IS somehow maintained despite the molecular turmoil. But there is an issue here that demands some specific theory. The stability of brain circuits cannot simply be taken for granted. Princeton University's Joe Tsien - famous for making mice smarter by splicing in slower-closing NMDA receptors - is one of a number of researchers pursuing the idea that synaptic structure may be stabilized by pressure from both above and below.