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Lecture 4

PSYC62H3 Lecture Notes - Lecture 4: Brain Stimulation Reward, Nucleus Accumbens, Psychoactive Drug

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Suzanne Erb

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Lecture 4 The Neurobiology of Reward
-These three don't always occurred during addiction and can occur in the absence of addiction
Drugs of abuse- have rewarding effects which cause individuals to enjoy taking the drug
- A reward can be something pleasurable, can take away unpleasant things, can have positive emotional valence, and
can serve as an incentive in the context of learning (eg: reinforcing) (positive or negative reinforcement)
-Something neutral that can produce reward is called classical or pavlov conditioning
-Individuals seek rewards and stimuli from the environment
Different types of rewards
•Natural rewards
•e.g., food, water, sex, nurturing
- Cause pleasure when procuring the rewards
- naturally adaptive roles
•Artificial rewards
•e.g., drugs, money (gambling)
- Act on the same brain systems that natural reward systems work on
Olds and Milner (1954)
• discovered that electrical stimulation of certain areas of the brain was rewarding and reinforcing
-They put a rat in a Skinner box with an electrode in the brain
-In the Skinner box was a lever that the rat could press to allow the region of the brain with the electrode to be
-They identified what brain regions are capable of maintaining brain stimulation of reward by looking at the region that
the rat self-stimulated by pressing the lever
-They found these regions capable of causing rats to self-stimulate

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Brain stimulation reward sites include: brain stimulation reward sites include:
•Medial Forebrain Bundle (MFB)
•Ventral Tegmental Area (VTA)
•Nucleus Accumbens
•Frontal Cortex
•Lateral Hypothalamus
•Substantia Nigra
•Striatum, Amygdala, Hippocampus, Thalamus, Cerebellum
•Locus Coeruleus
- Primary Reward Pathway: consists of MFB, VTA, Nucleus Accumbens and Frontal Cortex
- In particular the VTA and dopaminergic projections which is the primary reward pathway. The MFB's and
nucleus accumbens and prefrontal cortex are also part of the primary reward pathway.
• The DA hypothesis of reward has instigated a considerable amount of research over the last few decades.
• However, much of that research can lead one to conclude that it is oversimplified to consider DA as the sole
mediator of primary “reward”, or primary motivation for natural stimuli such as food, water, and sex.

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-Related behaviour to dopamine because the main projection region is dopamine and when stimulating, there is more
dopamine activity in the brain.
-Dopamine blockers stop rat from brain stimulating
-Graph microdialysis cerebrospinal fluid to test drug levels (100% = baseline)
• Imaging studies are often used to support the idea that nucleus accumbens mediates pleasure.
-Dopamine transmission especially in the nucleus accumbens of the primary pathway mediates all positive reinforcing
stimuli. Drugs of abuse hijack this pathway and cause it to react to both artificial and natural drugs differently.
-Drugs increase dopamine in nucleus accumbens
-Oversimplified to consider it dopamine (DA) as the sole mediator of the primary reward there is more factors
affecting this and humans use dopamine for more than just pleasure
-Nucleus accumbens also reacts to the adverse situations such as stress, aversion, hyper arousal/irritability
• But imaging research also demonstrates that the nucleus accumbens responds to:
• stress
• aversion
• hyperarousal/irritability
• Thus, concepts about role of DA in drug-induced euphoria, dependence, and addiction have undergone
-Benzodiazepam blocking dopamine can take away aversive effects
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