I got the recommendation for this book from Chris Chatman’s book list, and reading Steven Strogatz’s book was very much a pleasure. My nit-picks are that I wish it had had more actual math equations and fewer analogies, but those flaws are outweighed by the breadth of topics he covers. Here are some of my notes (assume it is a quote unless indicated by brackets):
Why do we need so many of these cells, if one can do the job by itself? Probably because a single leader is not a robust design–a leader can malfunction or die. Instead, evolution has produced a more reliable, democratic system, in which thousands of cells collectively set the pace.
Once two oscillators fire together, they will never drift apart on their own, because they have identical dynamics, furthermore, they are identically coupled to all the others, so even when they are kicked, they will stay in sync because they are jolted equally. Thus absorptions act like a ratchet, always bringing the system closer to synchrony.
Fireflies represent one of the few tractable instances of a complex, self-organizing system, where millions of interactions occur simultaneously–when everyone changes the state of everyone else. Virtually all the major unsolved problems in science today have this intricate character.
[Why do women show sync in their menstrual cycles? They are having a chemical dialogue]: It could be that women unconsciously strive to ovulate and conceive in step with their friends (to allow them to share child-rearing and breast-feeding duties) and to keep out of step with their enemies (to avoid competing with them for scarce resources).
“The great tragedy of science–the slaying of a beautiful theory by an ugly fact.” - T. H. Huxley.
[The sleep patterns of subjects isolated from the world]: During his first five weeks in the cave, Siffre unknowingly lived on a 26-hour cycle. He woke up about two hours later each day and drifted around the clock relative to the outside world, but otherwise maintained a normal schedule, sleeping about a third of the time.
Body temperature in a healthy person does not stay constant at 98.6 degrees F, or at any other number; it typically undulates through a range of about 1.5 degrees over the course of the day, even if we lie in bed an don’t exert ourselves.
How long a subject stayed a sleep did not depend on how long he had been awake beforehand; it depended on when he fell asleep in relation to his cycle of body temperature.
Alertness goes hand in hand with body temperature: It’s low when temperature is low and high when temperature is high.
Therefore, minimum alertness should occur around the time of the temperature through, namely, 4 to 6 AM…. Field studies show that from 3 to 5 AM, workers are slowest to answer a telephone, slowest to respond to a warning signal, and most apt to read a meter wrong.
The rule is that REM is most likely just after the part of the temperature cycle when your body is coldest. In 24-hour entrainment, that’s the circadian phase when most people wake up, which is why REM is so common at the end of sleep.
[Biological clock depends of the hypothalamus, when brain legions were tested in rats in most areas]: The rats went right on feeding, drinking, and running rhythmically–except when the lesions were placed in the front part of the hypothalamus. then the rats became arrhythmic.
Births are most likely to occur in the early morning, around 3-4 AM; the same is true of deaths, with the curious implication that we all tend to live an exact, whole number of days.
The synchronizing effect of light can be inferred from the fact that 80 percent of blind people have chronic sleep disorders.
[There is a difference between serendipity and luck.]
[How lasers work]: Every time a photon hits an excited atom, it duplicates itself, amplifying the amount of light traveling in that direction, which is precisely what the acronym laser stands form: Light Amplification by Stimulated Emission of Radiation. The emission is said to be stimulated (as opposed to spontaneous) because the incoming photon provoked the excited atom into spitting to the new photon.
The emitted photon is indistinguishable from the one that spawned it. If you think of these photons not as particles but as tiny waves of light, they’d be perfectly synchronized. All their peaks and valleys would be aligned, meaning that they’re carrying light of the same color, in the same direction and with the same phase.
Only the photons bouncing back and forth between the mirrors survive. And not only do they survive; the proliferate. With every rebound through the tube, they give birth to more and more perfect copies of themselves, reinforcing their light and creating a magnificent beam of perfectly synchronized photons. To let some of that light out, one of the mirrors is designed to be slightly less than 100 percent reflective. The tiny fraction of synchronized light that escapes is what we see as a laser beam.
In its technical sense, however, chaos refers to a state that only appears random, but is actually generated by nonrandom laws. As such, it occupies an unfamiliar middle ground between order and disorder. It looks erratic superficially, yet it contains cryptic patterns and is governed by rigid rules. It’s predictable in the short run but unpredictable in the long run. And it never repeats itself: Its behavior is nonperiodic.
But the rub is the obstinate way the predictability horizon depends on the initial precision: If you want to predict twice as long yet still achieve the same accuracy, it will now cost you not twice the effort but ten times as much. In a chaotic system, the required precision in the initial measurement grows exponentially, not linearly.
Normally a neuron is quiescent. With inadequate stimulation, it shows little response and returns to rest. But a sufficiently provocative stimulus will excite the neuron and cause it to fire. Next it becomes refractory (incapable of being excited for a while) and finally returns to quiescence. The parallels with chemical waves extend to action potentials, the electrical waves that propagate along nerve axons. They too travel without attenuation, and when two of them collide, they annihilate each other.
[The BZ reaction is an example of electrical waves in an excitable medium, and since these processes are all so similar studying it yields useful stuff about the brain.
For the tangle of neurons in the brain, where cells connect extensively to others nearby but also send long-range fibers halfway across the cortex, grids and lattices were clearly inappropriate. A better model of the geometry would incorporate a looser, more relaxed kind of structure, a hodgepodge of order and randomness, with clustered local connections and haphazard global ones.
[A classic puzzle in computer science is the “density classification problem for one-dimensional binary automata”, involves finding a local rule based on neighbors to cause all of nodes in a ring to turn on or off depending on whether more than half of the nodes are initially on or off.
A dumb rule (the majority rule) running on a smart architecture (a small world) achieved performances that broke the world record…. Small world architecture [with some random connections thrown in between various nodes in the ring] may be a powerful design for other problems of collective computation, one that confers surprising strength on even simpleminded local rules.
The most highly connected proteins are indeed the most important ones for the cell’s survival… the deletion of any of the kingpins (the top 1 percent of all proteins, each with 15 or more connections) proved deadly 62 percent of the time, [as opposed to a deletion of the peons (93% of proteins), which proved deadly only 21 percent of the time.]
Heterogeneity in the population has mixed effects. A broader range of thresholds destabilizes the system, making it more susceptible to fads (essentially because there are more early adopters to provide kindling), whereas a broader range in connectivity (greater variability in the number of neighbors per node) tends to stabilize it.
[Crazy experiment, there is a possibility that]: Electrical rhythms in our brains can be influenced by external signals. For instance, Norbert Winere described an outrageous experiment conducted in Germany in the 19502, in which the unnamed scientists attempted to synchronize a human subject’s brain waves by beaming high-power electromagnetic radiation at him. As Weiner tells it, a sheet of tin was suspended from the ceiling and connecting to one terminal of a 400-volt generator running at 10 cycles a second, the same frequency as the brain’s alpha rhythm. He writes that this apparatus “can produce electrostatic induction in anything in the room” and that “it can actually drive the brain, causing a decidedly unpleasant sensation.”
The intense optical stimulation caused by the pulsing, kaleidoscopic bursts of light apparently triggered attacks of photosensitive epilepsy, a rare disorder that has become much more common as television and video games have proliferated. The precise cause of photosensitive epilepsy is unknown, but it’s thought to be a synchronization disorder in which brain waves are entrained by flickering light, causing neurons in the brain to misfire in lockstep and produce a seizure. That hypothesis is consistent with the clinical observation that the most dangerous frequencies are between 15 and 20 cycles a second, just a bit faster than the brain’s alpha rhythm.
[Jurgen Fell et al (2001)]: They asked volunteers to memorize lists of words, and after briefly distracting them with another task, tested their recall. Meanwhile, during the memorization phase of the experiment, the scientists measured the firing patterns of neurons in the subject’s hippocampus and rhinal cortex, adjacent brain areas known to be involved in memory… These subjects were epileptics who already had electrodes implanted in their brains in preparation for upcoming neurosurgical procedures, which afforded an unusual opportunity to record directly from human brain cells during the act of memorization
A quarter of a second after viewing words that they’d later remember, their brains showed a rush of synchrony between the hippocampus and rhinal cortex, but there was no synchrony when they first viewed words they’d later forget.