NEURO2020 WEEK 10

MOTIVATION

• Motivation entails emotions and affective responses to stimuli  

• Pleasant = useful for survival

• Pleasure/displeasure codes for the survival value of stimuli 

REWARDS

Biologically 

• Food, water, sex, social closeness 

Social psychology  

• Achievement, intimacy, power, exploration 

Needs driven 

• Goals to satisfy a need or deficiency (like eating when hungry) 

Incentive driven 

• Goals that give pleasure but not necessarily satisfying a physiological need 

MOTIVATED BEHAVIOUR TYPES - APPROACH

• Individual actively seeks to get close to the goal 

• Action is terminated when the goal is attained 

MOTIVATED BEHAVIOUR TYPES - AVOID

• Inefficient strategy as an individual is never sure if they have done enough to attain the goal of avoidance. The absence of the outcome is the only cue to success.  

Active Avoidance  

• execution of behaviour to avoid an unpleasant stimulus or outcome 

Passive avoidance 

• inhibition of a behaviour to avoid an unpleasant stimulus or outcome 

TWO PHASES OF MOTIVATION

Motivation Phase  

• The organism works to attain a reward  

Consummation Phase 

• The organism evaluates the reward 

• If better than expected – motivation increases 

AMYGDALA

• Facilitates learning of signals indicating an attractive stimulus is nearby  

• Enables 'honing in' on rewards 

• Is connected to early sensory areas as well as higher cognitive areas 

  • Sensory = knee-jerk response to something that looks like a snake 

  • Cognitive = calmness and reflection of realising it is not  

STRIATUM

• Underlies the 'wanting' phase of motivation 

• Responsible for selection of behaviours aimed at incentives/away from disincentives 

• It is responsible for motivated movement 

NUCLEUS ACCUMBENS

• structure in the Dopamine reward system 

• Dopamine is released in response to a cue of a reward. If a reward is attained, this triggers the release of more dopamine. 

• stimulates strong behavioural urges

• Responsible for incentives (both positive and negative) 

 

RESPONSES FROM DOPAMINE STIATAL CELLS

• Monkey trained to associate glucose reward with predicted cue 

• Dopamine receiving cell fires strongly just after reward delivered 

• After training the dopamine cell responds strongly to the cue but stays at baseline to the actual reward 

• When a reward is predicted by the cue but not provided, the dopamine cell reduces its firing rate below baseline 

• Dopamine receiving neurons are thought to code for 'reward prediction errors' 

DOPAMINE AND REWARDS

• Rats in the high dose of dopamine approached the reward slower than rats with lower/no doses 

• However, they consumed just as much when they got there 

• Evidence that dopamine is involved in the 'wanting or incentive power' of the stimulus 

ORBITOFRONTROL CORTEX

• Is connected with amygdala and striatum and dopamine system 

• Responsible for evaluation stage of motivation 

• OFC activity is correlated with the organism's desire for a given reward 

OFC NEURON RESPONSE AND BEHAVIOUR

• Recordings were collected from a single OFC neuron that responds to sweet 

• Initial = strong response to first drops of glucose 

• As more glucose given, OFC neuron reduced its firing rate 

• The monkeys acceptance of the glucose reduced as the firing rate of the OFC reduced 

• After a break, the neuron firing rate and monkeys acceptance returned to normal 

REWARD AND ADDICTION

• Addiction follows the formation of a habit that serves to attain a reward, pleasure, or relief from some ailment. 

• Action is flexible but resource intensive 

• Habit is an inflexible representation specific to the stimulus and context in which they were learned 

BEFORE HABIT IS FORMED, ACTION IS:

• Purposeful, goal directed 

• Action outcome 

• If outcome rewarding – behaviour reinforced 

REPETITION AND ADDICTION

• With repetition, Dorsal Striatum chunks the task so that it is represented as a single event 

• The strength of the chunked representation increases with repetition until it becomes automatic  

• Habit is an autonomic response to a sensory cue  

HABIT

• A chunked representation stays stable as long as it is performed and at least partially rewarded 

• As a habit gets stronger, it becomes less sensitive to outcomes (REWARD INVARIANCE) 

• Dorsal striatum pattern decays when all rewards lose value, rewards are removed, contingency is explicitly changed.  

STRESS AND HABITS

Acute and chronic stress increase habit reliance  

• Impedes deliberate action control 

• Decreased activity in OFC and prefrontal cortex, which are areas for goal-directed learning 

ADDICTION

• Inability to refrain from behaviour despite adverse effects on health and social life, and despite repeated attempts to stop  

• Can be habitual user without being an addict 

• Compulsive, chronic and relapsing 

• Narrowing in diversity of motives 

• Not limited to drugs  

ADDICTION AND BLOOD-BRAIN BARRIER

• Many blood born chemicals cannot enter brain chemistry, but those that can: 

  • Act diffusely throughout CNS (ex. Alcohol) 

  • Bind to specific receptors (ex. Nicotine, THC, heroin) 

  • Influence synthesis, transport, release and deactivation (cocaine, MDMA) 

  • Influence chemical reactions elicited by post-synaptic neurons (LSD) 

• Drug metabolism 

  • Break-down of drugs into non-active forms 

ADDICTION TOLERANCE

• A state of decreased sensitivity to given drug after exposure to it  

• A given dose has less effect than it did previously  

• Shift in dose response curve to right  

• OCCURS WHEN DRUG GIVEN BEFORE CUE

METABOLIC TOLERANCE

• Results from changes that result in less drug getting to the site of action 

• Ex. Liver gets more efficient at breaking down alcohol 

FUNCTIONAL TOLERANCE

• Results from changes that reduce the reactivity of sites of action 

• The number of receptors available, efficiency of receptor sites 

• Ex. Heroin – opioid receptors become less responsive 

ADDICTION DEPENDENCE

• After several days of exposure to a drug, sudden elimination results in adverse physiological responses 

• Withdrawal effect gets weaker over time 

PATHWAY TO ADDICTION

• A shift from goal-directed behaviour to compulsive/habitual drug seeking and consumption 

• Initial drug taking is voluntary and reflects hedonic value or serves a purpose 

• Habitual drug taking: the value of the drug declines but the anticipated reward increases. Wanting >> liking. 

ATTENTION AND THREAT

Threatening stimuli capture our attention. People are faster to find an angry face amongst other expressions.

COGNITIVE MECHANISMS OF THREAT BIAS

Facilitated Attention:

• we detect threatening stimuli faster than non-threatening stimuli

Difficulty Disengaging

• we struggle to move our attention from threatening stimuli

FEAR-RELEVANT STIMULI

Some stimuli are frequently associated with danger in the natural environment - these are termed fear-relevant.

• certain animals such as snakes, spiders

• it aids survival for these fear-relevant animals to have priority in our attentional and cognitive systems

FEAR-RELEVANT ANIMALS AND ATTENTION

We are faster to detect the target when it appears on the same side as the fear-relevant animals.

• stronger effects found in individuals with greater levels of fear as they often struggle to disengage from threatening stimuli

FEAR AND VISUAL SEARCH

Spider fearful participants showed generally more attentional capture and distraction by spider stimuli than non-fearful controls. Therefore, the affective content of stimuli can influence our attention and fear-relevant animals can involuntarily capture our visual attention.

EMOTION AND MEMORY

• Events that evoke high levels of emotion are likely important to us

• the hippocampus (memories) is right next to the amygdala (emotion)

• the hippocampus and amygdala activate together to encode emotional information into long term memory = better retention