Blue Mars(252)

The original Hebb hypothesis, first proposed by Donald Hebb in 1949, was still held to be true, because it was such a general principle; learning changed some physical feature in the brain, and after that the changed feature somehow encoded the event learned. In Hebb’s time the physical feature (the engram) was conceived of as occurring somewhere on the synaptic level, and as there could be hundreds of thousands of synapses for each of the ten billion neurons in the brain, this gave researchers the impression that the brain might be capable of holding some 1014 data bits; at the time this seemed more than adequate to explain human consciousness. And as it was also within the realm of the possible for computers, it led to a brief vogue in the notion of strong artificial intelligence, as well as that era’s version of the “machine fallacy,” a variant of the pathetic fallacy, in which the brain was thought of as being something like the most powerful machine of the time. The work of the twenty-first and twenty-second century, however, had made it clear that there were no specific “engram” sites as such. Any number of experiments failed to locate these sites, including one in which various parts of rat’s brains were removed after they learned a task, with no part of the brain proving essential; the frustrated experimenters concluded that memory was “everywhere and nowhere,” leading to the analogy of brain to hologram, even sillier than all the other machine analogies; but they were stumped, they were flailing. Later experiments clarified things; it became obvious that all the actions of consciousness were taking place on a level far smaller even than that of neurons; this was associated in Sax’s mind with the general miniaturization of scientific attention through the twenty-second century. In that finer-grained appraisal they had begun investigating the cytoskeletons of neuron cells, which were internal arrays of microtubules, with protein bridges between the microtubules. The microtubules’ structure consisted of hollow tubes made of thirteen columns of tubulin dimers, peanut-shaped globular protein pairs, each about eight-by-four-by-four nanometers, existing in two different configurations, depending on their electrical polarization. So the dimers represented a possible on-off switch of the hoped-for engram; but they were so small that the electrical state of each dimer was influenced by the dimers around it, because of van der Waals interactions between them. So messages of all kinds could be propagated along each microtubule column, and along the protein bridges connecting them. Then most recently had come yet another step in miniaturization: each dimer contained about 450 amino acids, which could retain information by changes in the sequences of amino acids. And contained inside the dimer columns were tiny threads of water in an ordered state, a state called vicinal water, and this vicinal water was capable of conveying quantum-coherent oscillations for the length of the tubule. A great number of experiments on living monkey brains, with miniaturized instrumentation of many different kinds, had established that while consciousness was thinking, amino-acid sequences were shifting, tubulin dimers in many different places in the brain were changing configuration, in pulsed phases; microtubules were moving, sometimes growing; and on a much larger scale, dendrite spines then grew and made new connections, sometimes changing synapses permanently, sometimes not.

So now the best current model had it that memories were encoded (somehow) as standing patterns of quantumcoherent oscillations, set up by changes in the microtubules and their constituent parts, all working in patterns inside the neurons. Although there were now researchers who speculated that there could be significant action at even finer ultramicroscopic levels, permanently beyond their ability to investigate (familiar refrain); some saw traces of signs that the oscillations were structured in the kind of spin-network patterns that Bao’s work described, in knotted nodes and networks that Sax found eerily reminiscent of the palace-of-memory plan, utilizing rooms and hallways, as if the ancient Greeks by introspection alone had intuited the very geometry of timespace.

In any case, it was sure that these ultramicroscopic actions were implicated in the brain’s plasticity; they were part of how the brain learned and then remembered. So memory was happening at a far smaller level than had been previously imagined, which gave the brain a much higher computational possibility than before, up to perhaps 1024 operations per second— or even 1043 in some calculations, leading one researcher to note that every human mind was in a certain sense more complicated that all the rest of the universe (minus its other consciousnesses, of course). Sax found this suspiciously like the strong anthropic phantoms seen elsewhere in cosmological theory, but it was an interesting idea to contemplate.