# Behave by Robert Sapolsky
## One Second Before

There is no single reason behind an action (a behaviour). It is the chain of events, culmination of years of life lived by the individual, hormonic or biological state, and millions of years of (evolutionary) experience aggregated by the species as a whole, etc that impacts each individual. We can't put a finger at a point and say this is "the" reason. The last checkpoint right before a behaviour happens is the brain. This chapter deals with the neurobiology of the event/action/behaviour.

### THREE METAPHORICAL LAYERS
1. **Ancient Brain / Stem (Automatic / Regulatory)**
Found in all animals. Things like breathing, body temperature are controlled from within
2. **Limbic system**
Found in mammals. Emotions.
3. **Cortex** Cognition, memory storage, sensory processing, abstractions, philosophy, navel contemplation.

All three layers talk with each other, influence each other.

### LIMBIC SYSTEM
Rodent <= Olfaction (smells)
Humans <= Visuals

There are no regions in brain associating with one particular behaviour. There maybe some, for other things. For instance, there's a region responsible for left pinkie's bend. Some center-ish: body temperature, breathing.

#### ANS (Autonomic Nervous System)
* **PNS** (Parasypathetic Nervous System): Vegetative states -- Promotes digestion.
* **SNS** (Sympathetic Nervous System): Activated when excited (Fear, Fight, Flight, and sex). Inhibits PNS

#### Limbic System x Cortex

`
as shown by the temperature of a cup—something processed in the hypothalamus—altering assessment of the coldness of someone’s personality. Emotions filter the nature and accuracy of what is remembered. Stroke damage to certain cortical regions blocks the ability to speak; some sufferers reroute the cerebral world of speech through emotive, limbic detours—they can sing what they want to say. The cortex and limbic system are not separate, as scads of axonal projections course between the two. Crucially, those projections are bidirectional—the limbic system talks to the cortex, rather than merely being reined in by it. The false dichotomy between thought and feeling is presented in the classic Descartes’ Error, by the neurologist Antonio Damasio of the University of Southern California; his work is discussed later.`

#### THE AMYGDALA
Sits under cortex in the temporal lobe. Central to mediating aggression, fear, and anxiety.
* Lesion amygdala => Rates of aggression _declines_
* Seeing image that provokes anger => Activates amygdala
* Stimulate amygdala with an electrode => Produces rage
* Destroyed amygdala => Person unable to recognise angry facial expressions

`Crucially, the brain region most involved in feeling afraid and anxious is most involved in generating aggression. The amygdala/fear link is based on evidence similar to that supporting the amygdala/aggression link.`

* Human amygdala responds to fear evoking stimuli. Unpredictability of fearful events.
* Sensitive to unsettling social circumstances.

`activating specific circuits within the amygdala in mice turns anxiety on and off; activating others made mice unable to distinguish between safe and anxiety-producing settings.`

* Innate Fear: Individuals are born with some types of fears. Think snakes. Makes sense from evolution's point of view. An [interesting video clip](https://www.youtube.com/watch?v=B3OjfK0t1XM) from BBC's Planet Earth II.
* Learned Fear: Fear can be conditioned. A crawling toddler touching the bright, inviting tip of a burning incense. BLA (Basolateral amygdala) is involved in learning fears. All sensory signals are always sent to BLA. The fearful ones (based on condition) get meaning -- don't touch that again! -- New circuits are formed for new fears. Learned fears can be unleared. FC inhibits circuits involved in learned fears.

`The amygdala isn’t about the pleasure of experiencing pleasure. It’s about the uncertain, unsettled yearning for a potential pleasure, the anxiety and fear and anger that the reward may be smaller than anticipated, or may not even happen. It’s about how many of our pleasures and our pursuits of them contain a corrosive vein of disease`

#### Amygdala inputs
* **Sensory Inputs**: Our visual, auditory senses are interpreted in cortex. This takes time. They are directly connected to amygdala as well, albeit with reduced accuracy. In some situations
* **Pain (PAG)**: Reliable trigger for fear and aggression. It is not the pain itself that might activate amygdala, but the unpredictable one. Pain, and amygdala's response is again dependent on context.
* **Disgust (Insular cortext)**: For humans, this is involved in both _bite into rancid food_, and thinking of something _morally disgusting_.
* **Frontal Cortex**

#### Amygdala Outputs
* **Bidirectional connections**: FC, Insula, PAG, sensory projections
* **Hippocampus**: Eg. Contextual information about fearful situations.
* **Motor Outputs**: Shortcut sensory connections might evoke some action, making amygdala directing body movements. See a lion? RUN!
* **Arousal**: TBW

### THE FRONTAL CORTEX

Working memory, executive function, organize knowledge, gratification postponement, long-term planning, controlling emotions, impulses

_Makes you do the harder thing_

#### Subregions
* PFC (Prefrontal cortex, decider/executive)
* Mortor cortex
* Insular cortex
* Sensory regions
* etc..

#### FC and cognition
Organises rules/knowledge graph, refer to them while making decisions. Comes up with strategies to organise information => for new data points, try and link them with existing data points so as to make connections between them. This network is referred for decisions.

_Labels/categorical thinking_
Experiment: Monkeys trained to differentiate between cats & dogs. PFC contained individual neurons for pictures of monkey, and cat. Respective correct neuron would fire, even with 40:60 ratio of a hybrid picture.

PFC also has inhibitory circuits, _probably_ refers to the rules / knowledge graph mentioned before, which are involved in inhibiting certain behaviours / actions. `Fun examples`: stop, those aren’t your cookies; you’ll go to hell; self-discipline is good; you’re happier when you’re thinner—all giving some lone inhibitory motor neuron more of a fighting chance.

#### Frontal metabolism and vulnerability
Von Economo (Spindle) cells are expensive. Track a lot of rules, talk with a lot of other parts of the brain (networks), have to be involved in most of inhibitory decisions. `Frontal cortical neurons are generalists, with broad patterns of projections, which makes for more work`.

Hard work (cognitive load) =>
* Performance declines in subsequent cognitively hard tasks.
* Subjects become less social, charitable, likely to help

Often, some tasks that require the involvement of FC, get transferred to autonomous parts of the brain. Example: Learning to play a tune on piano. Intially hard, is later transferred to cerebellum (becomes autonomous / muscle memory kinda thing). The same is true for moral acts.

#### FC and social behaviour
Bigger the social group => larger the size of FC.
Fission-fusion groups => larger FC

Monkeys belonging to fission-fusion kind of groups have better inhibitory control over non-fission-fusion groups.

`We utilize the frontal cortex to do the harder thing in social contexts—we praise the hosts for the inedible dinner; refrain from hitting the infuriating coworker; don’t make sexual advances to someone, despite our fantasies; don’t belch loudly during the eulogy.`

**Damage to frontal-cortex** results in loss of inhibitions in social context.

#### Descartes' error (thought v emotion)

Two parts of the PFC involved in decision making
1. dlPFC - rational, cognitive, unsentimental, utalitarian
2. vmPFC - emotions; talks to limbic system

vmPFC gives negative feedback, thus helps in shifting behaviour. Helps FC run "simulations" of future events to figure out how the resultant event would feel. That is taken into consideration by PFC to make decisions.

`A simplistic view is that the vmPFC and dlPFC perpetually battle for domination by emotion versus cognition. But while emotion and cognition can be somewhat separable, they’re rarely in opposition. Instead they are intertwined in a collaborative relationship needed for normal function, and as tasks with both emotive and cognitive components become more difficult (making an increasingly complex economic decision in a setting that is increasingly unfair), activity in the two structures becomes more synchronized.`

#### FC x limbic system

* PFC is the one who tells BLA to inhibit that learned fear activation
* PFC can control emotions (think of something else / CBT), reason about the situation - silencing dlPFC/limbic system

Anger/Anxiety have affects our interpretations, and our impacts decisions.

### LIMBIC / CORTICAL DOPAMINE SYSTEM
`REWARD, PLEASURE, AND happiness are complex, and the motivated pursuit of them occurs in at least a rudimentary form in many species. The neurotransmitter dopamine is central to understanding this`
* Synthesized in multiple brain regions, including
* Region responsible for movement
* Release of a pituitary hormone
* We are concerned with Ventral Tegmental area (key target for projection is nucleas accumbens)

#### REWARD
Some observations with supporting evidence:
1. Drugs (cocain, heroin, alco) release dopamine in the accumbens
2. If the release is blocked, rewarding stimuli becomes aversive
3. Stress, pain depletes. decreases sensitivity of dopamine accepting neurons. anhedonia -- the inability to feel pleasure.

* Unlike other species, in humans, just imagining pleasurable events releases dopamine.
* Mesolimbic ckt responds to pleasurable aesthetics. Think music.

#### Habituation of Reward
1. Monkey presses lever 10 times, receives 1 raisin => 10 u of dopamines
2. Monkey presses lever 10 times, receives **2** raisin => **20** u of dopamines
3. Continue receiving 2 raisins, the size of dopamine comes down to 10 u
4. Reward the monkey with a single raisin: Dopamine comes down.

Everything is hooked into the same reward circuit and it has to accommodate for everything else as well. Eg, solving math, having orgasm.

`Dopaminergic responses to reward, rather than being absolute, are relative to the reward value of alternative outcomes. In order to accommodate the pleasures of both mathematics and orgasms, the system must constantly rescale to accommodate the range of intensity offered by particular stimuli. The response to any reward must habituate with repetition, so that the system can respond over its full range to the next new thing`

**"Must constantly rescale"**.

* Expected result => Steady dribble of Dopamine
* Better, Earlier => Increase
* Worse, Later => Decrease

*Tegmentam, and accumbens get projections from FC where the expectancy/discrepancy is calculated.*