chapter 2, one second before

Once, we had lives that, amid considerable privation, also offered numerous subtle, hard-won pleasures. And now we have drugs that cause spasms of pleasure and dopamine release a thousandfold higher than anything stimulated in our old drug-free world.
An emptiness comes from this combination of over-the-top nonnatural sources of reward and the inevitability of habituation; this is because unnaturally strong explosions of synthetic experience and sensation and pleasure evoke unnaturally strong degrees of habituation. 
... the pleasure is in the anticipation of reward, and the reward itself is nearly an afterthought (unless, of course, the reward fails to arrive, in which case it's the most important thing in the world). ... so dopamine is more about anticipation of reward than about reward itself. ... the happiness of pursuit of reward that has a decent chance of occurring. 

chapter 4, hours to days before

Testosterone increases anxiety — you feel threatened and become more reactively aggressive. Testosterone decreases anxiety — you feel cocky and overconfident, become more preemptively aggressive. ... This context dependency means that rather causing X, testosterone amplifies the power of something else to cause X.
Testosterone makes us more willing to do what it takes to attain and maintain status. ... Engineer social circumstances right, and boosting testosterone levels during a challenge would make people compete like crazy to do the most acts of random kindness. In our world riddled with male violence, the problem isn't that testosterone can increase levels of aggression. The problem is the frequency with which we reward aggression.
Oxytocin, the luv hormone, makes us more prosocial to Us and worse to everyone else. That's not generic prosociality. That's ethnocentrism and xenophobia. In other words, the actions of these neuropeptides depend dramatically on context — who you are, your environment, and who that person is.
We get sick from activation the stress response too often, too long, and for purely psychological reasons.
The core of psychological stress is lost of control and predictability. But in benevolent settings we happily relinquish control and predictability to be challenged by the unexpected.
Hormones don't determine, command, cause, or invent behaviors. Instead they make us more sensitive to the social triggers of emotionally laden behaviors and exaggerate our preexisting tendencies in those domains. 

chapter 5, days to months before

The experience alters the number and strength of synapses, the extent of dendritic arbor, and the projection targets of axons. [remapping]
Experience, health, and hormone fluctuations can change the size of parts of the brain in a matter of months. [hippocampus, London cabbies]

chapter 6, adolescence: or, dude, where's my frontal cortex?

As emphatic pain increases, your own pain becomes your primary concern. In contrast, the more individuals can regulate their adverse emphatic emotions, the more likely they are to act prosocially. ... Thus, one predictor of who actually acts is the ability to gain some detachment, to ride, rather than be submerged, by the wave of empathy.
Because it is the last one to mature, by definition the frontal cortex is the brain region least constrained by genes and most sculpted by experience.

chapter 7, back to the crib, back to the womb

Does moral reasoning predict moral action? Rarely ... moral heroism rarely arises from super-duper frontal cortical willpower. Instead, it happens when the right thing isn't the harder thing.
... in young rats, even aversive things are reinforcing in Mom's presence, even if Mom is the source of the aversive stimuli. As Sullivan and colleagues wrote, "attachment [by such an infant] to the caretaker has evolved to ensure that the infant forms a bond to that caregiver regardless of the quality of care received." ... If this applies to humans, it helps explain why individuals abused as kids are as adults prone toward relationships in which they are abused by their partner.

Play is vital. In order to play, animals forgot foraging, expend calories, make themselves distracted and conspicuous to predators. Young organisms squander energy on play during famines. A child deprived of or disinterested in play rarely has a socially fulfilling adult life.
... the opposite of play is not work — it's depression.