PSYC 2: Biological Foundations - Fall 2012 - Professor Claffey

Notes: Cognition 3

Version:
11/26/12 - original version

Motivation & Reward

Questions:
    How can experimenters manipulate the brain directly to drive behavior?
    What happens in the brain when an experience is rewarding?
    How are reward and learning related in the brain?

Experiment: Lever Press

Source: sccpsy101.com/home/chapter-4/section-16/

Task:
    Animals learn to press a lever to have a reward delivered
    Rewards: food, water, sexual mates, drugs

Result:
    Animals will lever press 100s of times per hour for reward

this is __________________
        learning to behave in a way to produce a favorable outcome

contrasts with ____________________

learning that two things are associated but doesn't require any action/behavior for the subject

(like ____________________ task)

Experiment: Intracrancial self-stimulation (ICSS)

Discovered by Olds and Milner (1954)

Task:
Animal has electrode implanted into certain brain areas

(exact areas described below, doesn't work in most areas)

Same as lever press task, but instead of a physical reward the

animal's brain is electrically stimulated

Result:
Rats will press the bar 1000s of times per hour for stimulation
Rats will forgo food in favor of ICSS to the point of starvation

(Wise, 2002)

Theory:

The areas were electrodes can produce extensive self-stimulation are the "pleasure centers" of the brain

Dopamine & Intracranial Self-stimulation (ICSS)

review:
    dopamine - a monoamine neurotransmitter like _______________________________________________
    Produced by cells in the brain stem and released broadly throughout brain

background:
    ________________________ dopamine system - a group of neurons involved in distributing dopamine in the brain
    more in "Pathways" section below

Findings that imply that dopamine is involved in ICSS
    Most of the sites of self-stimulation are in the mesocorticolimbic dopamine system
    Lesions of the mesocorticolimbic system disrupt self-stimulation
    Stimulation increases release of dopamine
    Dopamine agonists increase self-stimulation and antagonists decrease it

Summary: dopamine seems to be critical to self-stimulation and reward seeking behavior

Dopamine Pathways

Mesotelenchephalonic dopamine system

Neurons that produce dopamine have cell bodies in the:

substantia nigra

project to dorsal striatum (basal ganglia)
nigrostriatal pathway
involved in ____________________________

ventral tegmental area (VTA)

project to cortex including nucleus accumbens
(and other areas)
mesocorticolimbic pathway
involved in ____________________________

Nucleus Accumbens - site of _______________________________

Dopamine, Learning & Reward

Review: Schultz, J Neurophys, 1997

Task:

Electrodes recording from dopaminergic neurons in

substantia nigra & VTA

Animals learn that a conditioned stimulus (CS) predicts a reward

Results:

If a reward comes unexpectedly, dopamine neurons fire

If the CS predicts a reward, dopamine neurons fire at CS but not for the reward

If the CS predicts a reward but the reward doesn't arrive, neurons are inhibited at time of expected reward

Summary:

Dopaminergic neurons don't simply fire at a rewarding experience, but at ____________________________ reward

Dopamine aids learning by signalling ____________ events and may facilitating synaptic changes

Theory:

We don't have a "pleasure system" just because it feels good - organisms consumed with pursuing pleasure for its own sake would probably not be adaptive.

Our "pleasure system" is an important and possibly critical part of ____________. By drawing our attention to unexpected, positive outcomes, we focus on and try to repeat behavior that produces these better outcomes.

Addiction

Theory:
    drug addiction involves reward-seeking behavior
    reward-seeking behavior (ICSS) involves the mesocorticolimbic system
    does drug addiction depend on the mesocorticolimbic system and dopamine?

Drugs that affect dopamine
    Cocaine - blocks dopamine ____________ (more dopamine in the synapse)
    Amphetamine - ______________ dopamine reuptake (more dopamine in the synapse)
    but not all drugs act on dopamine, so dopamine can't be the only answer
        (morphine on opiod receptors, MDMA on serotonin)

Evidence for Dopamine & Addiction

Animals will self-administer addictive drugs, similar to how they behave with ICSS
    Dopamine antagonists block self-administration of drugs and rewarding aspects of food
    Lesions to nucleus accumbens or VTA block self-administration of drugs
    Drugs and other reinforcers are associated with elevated dopamine in nucleus accumbens

Source: Volkow et al, 2009

PET scan (positron emissions tomography)

- Uses radioactive isotopes to observe where molecular reactions are occurring in the brain

- Not precise in time, somewhat precise in location, but allows for
observing specific ____________________

Result:

Ratings of how pleasurable a high is correlate with:

increasing cocaine dose and PET cocaine binding with dopamine receptors (Volkow et al, 2004)

increasing amphetamine dose and PET levels of dopamine in the nucleus accumbens (Drevets et al, 2001)

Meth abusers have less dopamine binding to dopamine receptors than non-using control subjects (Volkow et al, 2009)

Theory of Dopamine & Addiction

Drugs that affect synaptic dopamine are short-circuiting the dopamine reward/learning system

During drug use, there is excessive dopamine activity compared to typical, daily rewards

With excessive dopamine activity, neurons produce ____________ dopamine receptors
the dopamine signal is so strong, less receptors are needed to get the message
this is an example of ____________________

With less dopamine receptors, drug users are less likely to experience pleasure from daily experiences, which involve much less dopamine compared to drug use.

NOTE: cocaine & amphetamine-like drugs interact directly with dopamine reuptake/receptors

most other drugs do not interact directly with dopamine reuptake (e.g. morphine interacts with opiod receptors)
this is not the only mechanism for drug-induced reward and addiction

Emotions

Everyday concepts of emotions: feelings, moods, simple (fear) vs complex (guilt), cultural
    hard to define / agree

Emotions are part of adaptive behaviors
    Avoid aversive stimuli
    Seek rewarding stimuli
    Communicate with other animals of the same species

Past Theories

Around 1900, there was a "chicken or the egg" question regarding emotions
    Do emotions -> physical reactions (see the bear -> feel scared -> heart races)
    Or physical reactions -> emotions (see the bear -> heart races -> feel scared)
    Wasn't clear resolution to this question

As modern psychology was emerging around 1960, emotions were largely ignored
    considered undefinable (could not be ____________________ ) so not worth studying

In last 2 decades, neuroscientists like Joseph LeDoux & Antonio Damasio have reopened their study

"Emotions are specific and consistent collections of physiological responses triggered by certain brain systems when the organism represents certain objects of situations" - Antonio Damasio

studying emotions by examining ____________________________ and ____________________

Limbic System

Limbic system - a collection of structures with a role in emotional behavior

Limbic system is ____________________ across mammals

Compared to lower mammals, primates have a smaller proportion dedicated to limbic because the frontal cortex expanded

Amygdala

Revisited: Fear conditioning

Lesions to the amygdala ________________________ the freezing response
Amygdala sends output to areas responsible for the physical reactions (like hypothalamus)
    Freezing, piloerection, cardiovascular response
Amygdala forms simple associations between stimuli and positive/negative experience
    ________________________________
Review: What did the hippocampus do?
    Theory: The hippocampus recognizes/remembers the context, the amygdala binds the context to fear

Human: Amygdala & Fear

Task:
   subjects observe different facial emotions during fMRI
Result:
    amydala response is maximal for fearful faces
Theory:
    Is amygdala needed for experiencing or understanding emotions?
    Understanding may require experiencing the emotion for oneself

amygdala face processing morris

Source: Morris et al, Nature 1996

Patients with Urbach-Wiethe disease (destroys the amygdala) are particularly deficient in describing/recognizing fear

urbach wiethe fear drawning adolphs

Source: Adolphs... & Damasio, Neuroscience 1995

Amygdala: Not only for fear

Patient DR had amygdala lesion (Scott et al, 1997)
Could recognize faces but not the emotion (especially not fear)
Also could not recognize emotional content of written or heard words

Hypothalamus

Diverse functions: controls or involved in: hormone release, temperature regulation,food & water intake, sexual behavior, daily cycles, emotional responses

Output to autonomic nervous system (ANS) to quickly control:
heart rate, digestion, respiration, salivation, perspiration, pupil dialation, sexual arousal
Output to endocrine system
____________________________________________________

    ____________________________
    affects digestion, immune system, sexual arousal, energy levels, mood
    related neurohormones: cortisol, epinephrine (adrenaline), norepinephrine

Role in emotion
serves as the interface between cognitive and ____________________________

Hippocampus

May not be directly involved in emotional associations,
but sometimes necessary for remembering stimuli that enter into emotional associations
(see "Revisted: Fear conditioning" above)

Prefrontal Cortex

Seat of executive functioning: impulse control, decision making, delayed gratification
The prefrontal cortex (hopefully) inhibits or tempers emotional reactions

Decorticate cat

Source: michaeldmann.net/mann16.html

Cat had entire cortex removed
    Left basal ganglia, limbic system, brain stem

Could do automatic behaviors like walking if placed on a treadmill

Cat was prone to ____________________
    Aggressive / violent behavior with little or no provocation
    Must have hypothalamus intact
    Lack of cortex to inhibit inappropriate emotional reactions

Stress

stress - direct threats, perceived threats, feelings of strain

Pathways

Brain
Limbic system - perceive directly stressful stimuli (fear conditioning)
Cortex - interpret complex situations as stressful (is my boss mad?)

Hypothalamus - interface with pituitary gland & endocrine system

Anterior pituitary system

Release ____________________________ from adrenal cortex
mobilize energy, combat inflammation, assist in healing
release ____________________ - natural pain killers

Sympathetic nervous system

Release ____________ and ____________ (EPI = adrenaline)
Norepinephrine & epinephrine physically mobilize the body,
but circulating NOR/EPI also improve encoding of memories
Help "lock in" important stimuli
(remember the threat/experience)

Stress as Adaptive

In life threatening situations
    Mobilizes the body, reduces perception of pain
In critical learning situations
    EPI/NOR improve sensation & memory
In brief, manageable situations - ____________ stress
    Boast the immune response

Stress as Maladaptive

In ongoing, unmanageable situations - ____________ stress
Prevents the body from returning to homeostasis
Weakens the immune system, poor tissue growth, energy mismanagement, depression

Serotonin

Source: en.wikipedia.org/wiki/Serotonin

Review:

A monoamine neurotransmitter (same family as dopamine, epinephrine, norephinephrine)
Released from neurons with cell bodies in brain stem and distributed to a diverse brain areas

Released from raphe nuclei in brain stem

in simpler organisms, including ____________________ serotonin is primarily involved with ____________ behavior
    roughly 80-90% of the human body's serotonin is in the gut, 10% in the CNS

Can produce feelings of satiety (having enough food)
    With sufficient serotonin, rats consume less food and shift away from fatty foods (Clifton, 2000)

Low serotonin is associated with agitation & sluggishness

Depression - helped by increased serotonin in synapses
    Selective serotonin reuptake inhibits (SSRI) - fluoxetine (____________) was first SSRI to be approved

regulates ______________________________________

Drugs that act on serotonin:
    psilocybin (shrooms), mescaline, LSD, MDMA are agonists of the serotonin receptors

Summary:
    a sense of satiety/well-being is associated with proper serotonin functioning

Summary

Dopamine is critically involved in pleasure, reward and the motivation to learn
Amygala is the site of simple emotional memories - notably but not only fear
Hypothalamus is the gateway to physiological responses, which are fundamental to emotion reactions
Prefrontal cortex is involved in overriding or reconsidering our emotional reactions
Proper serotonin functioning is associated with a sense of satiety and well-being