Astralcodexten has a new post on amygdalectomy, i.e. surgically eliminating the amygdala from the brain (ideally noninvasively, though for the guest author it happened incidentally in a much larger cancer operation). This was something David and I had previously speculated about, so I'm pretty excited to see any account of it, and even more excited about the big positive effects the guy saw.
My background mental model here is that humans have various physiological knobs to turn, and many of those are set by evolution to levels which are much worse in the modern environment than the ancestral environment. For instance:
* In the ancestral environment, infection was a top killer. Today it's a rounding error. Our immune systems are therefore set by evolution to be far too sensitive for the modern environment.
* In the ancestral environment, food was much less abundant, so our bodies can use energy a lot more liberally today. In particular, this means thyroid levels are best on the high end of the normal range (but still not hyperthyroid); within the normal range, it's a lot better to be generally high-energy than low-energy.
* The modern environment just generally has way less risk than the ancestral environment, and therefore humans' general levels of anxiety, fear and stress are just ridiculously too high. This is where an amygdalectomy comes in: nuking the amygdala is the obvious way to permanently turn down the fear-and-anxiety knob.
The challenge, of course, is adjusting those knobs in a way that doesn't cause a cascade of other problems.
Notably, the ACX post says (very tentatively) that the guy's amygdala removal came with a pretty big IQ increase (7 points)! I'd be surprised if the effect is typically that large, but the IQ increase itself is a hypothesis I would have at least privileged beforehand. The mental model behind that part: in LLMs, people informally observe that RL training seems to make the LLMs stupider relative to their purely-predictive pre
