Science of stress - Robert Sapolsky Flashcards
Homeostasis is having an ideal body temperature, an ideal level of glucose in the bloodstream, an ideal everything. That’s being in homeostatic balance.
A stressor is anything in the outside world that knocks you out of homeostatic balance e.g if you’re a zebra and a lion has ripped your stomach open.
For 99 percent of the planet’s species, stress is three minutes of screaming terror in the savannah, after which either it’s over with or you’re over with.
We humans turn on the stress response with memories, with emotions, with thoughts, and the whole punch line is: That’s not what it evolved for.
Do it regularly enough, and you’re going to damage your cardiovascular system. Increased blood flow hammers on the walls of your blood vessels, causing inflammation. Fat and glucose and cholesterol begin to clog your arteries. You are more at risk for chronic fatigue, sleep disruption, muscle atrophy, and probably most importantly, diabetes.
Stress kills neurons in the part of the brain called the hippocampus and weakens the cables between neurons, so they can’t talk to each other. This impairs the formation and retrieval of long-term memory. The opposite thing happens in the amygdala, which is where we see fear in a brain scanner. In the hippocampus, stress causes stuff to shrivel up. But stress feeds the amygdala. It actually gets bigger. Chronic stress creates a hyper-reactive, hysterical amygdala, and this tells us tons about what stress has to do with anxiety disorders.
Dopamine is a neurotransmitter that is about reward and pleasure. Cocaine works on the dopamine system. What are the effects of chronic stress on this part of the brain? Those pathways get depleted of dopamine, and this takes away your ability to feel pleasure. So if stress depletes your dopamine, what have you just set yourself up for? Major depression.
What about the frontal cortex? It’s the most human part of the brain; we’ve proportionally got more of it than any other species does. And what does the frontal cortex do? It does gratification postponement, self-discipline, long-term planning, emotional regulation. It’s the last part of the brain to fully mature—that doesn’t happen until you’re 25 years old, which explains a lot about the freshmen year of college.
This has a very interesting implication. If this is the last part of the brain to fully develop, by definition, then, it is the part of the brain least constrained by genes and most sculpted by experience. What does chronic stress do to the frontal cortex? Atrophy of neurons, disconnecting circuits. As a result, you make the most idiotic decisions, which are going to haunt you for the rest of your life, and yet you think they’re brilliant at the time. That’s another effect of chronic stress: Your judgment goes down the tubes.
The emergence of stress as a major risk factor is testament to scientific progress: the deadliest diseases of the 21st century are those in which damage accumulates over time. (Sapolsky refers to this as the “luxury of slowly falling apart”.) Unfortunately, this damage is exacerbated by stress.
After his trip in 1978, Sapolsky began spending every summer in Kenya. In the early 80s, he happened upon a rare event: the highest-ranking female and a low-ranking one gave birth to daughters just days apart, and these newcomers allowed him to compare the effects of status on development. The first thing he noticed was that the high-ranking daughter hit every developmental landmark faster. She walked first, ate solid food earlier and interacted more with other baboons. The lesson, Sapolsky says, is that “status comes with privileges”, which are present from birth.
On one hand, stress can be described as a by-product of a society that leaves people in a state of unease. But that feeling can now be measured in blood and urine, quantified in terms of glucocorticoids and adrenal hormones. And we are starting to see, with scary precision, the devastating cascade unleashed by these chemicals. The end result is that stress is finally being recognised as a critical risk factor, predicting an ever larger percentage of health outcomes.
Stress is a chemical problem. When it occurs, a tiny circuit in the brain triggers the release of glucocorticoids, a family of stress hormones that puts the body in a heightened state of alert. The molecules are named after their ability to increase glucose levels in the blood, thus providing muscles with a burst of energy. They also shut down all non-essential bodily processes, such as digestion and the immune response. “This is just the body being efficient,” Sapolsky says.
But glucocorticoids have a nasty side effect: when they linger in the bloodstream, as they might due to chronic stress, damage accumulates. It’s the physiological version of a government devoting too many resources to its defence department, Sapolsky says. The body is so worried about war that it doesn’t fix the roads or invest in schools.
Interestingly, the effects of stress appear particularly toxic to the brain. When stress becomes chronic, neurons simply stop investing in themselves. Neurogenesis slows and dendrites (the branches of a neuron) shrink. In fact, the very act of keeping primates in standard lab enclosures – often just bare wire cages – is so stressful that for years scientists had a warped understanding of the primate brain. Gould has become an ardent advocate of “enriched enclosures”, which provide the animals with things to play with and social interaction.
These cellular alterations help to explain why, as researchers noted in a recent review article, a “large part of the changes in brain structure and function (induced by chronic stress) have similar characteristics to those observed in neurodegenerative diseases, most notably Alzheimer’s.” And the higher the level of stress hormone, then the greater the level of cognitive decline.
One of the most tragic aspects of the stress response is the way it gets hard-wired at a young age – an early setback can permanently alter the way we deal with future stressors. The biological logic of this system is impeccable: if the world is a rough and scary place, then the brain assumes it should invest more in our stress machinery, which will make us extremely wary and alert. There’s also a positive feedback loop at work, so that chronic stress actually makes us more sensitive to the effects of stress.
The physiology underlying this response has been revealed in the laboratory. When rats are stressed repeatedly, the amygdala – an almond-shaped nub in the centre of the brain – enlarges dramatically. (This swelling comes at the expense of the hippocampus, which is crucial for learning and memory and shrinks under severe stress.) The main job of the amygdala is to perceive danger and help to generate the stress response; it’s the brain area turned on by dark alleys and Hitchcock movies.
Unfortunately, a swollen amygdala means that we’re more likely to notice potential threats in the first place, which means we spend more time in a state of anxiety. (This helps to explain why a more active amygdala is closely correlated with atherosclerosis.) The end result is that we become more vulnerable to the very thing that’s killing us.
Scientists have been able to trace physiological connections from external inequality to three key inner areas: chronic inflammation, chromosomal aging and brain function.
What’s clear by now is if you have a choice between being a high-ranking baboon or a socially affiliated one, the latter is definitely the one that is going to lead to a healthier, longer life. That’s the baboon we want to be—not the one with power, but the one with friends, neighbors, and family.
