Reward System Flashcards
Behaviors
Pain to avoid, Pleasure to approach
Olds and Milner
a rat would seek to continue stimulation from a thin electrode implanted in certain parts of his brain.
It could reach a level of OCD
Choosing stimulation over food even when starving
Tremblay and Schultz
Monkey
The size of the signal is believed to represent motivational value, raisin > apple
OFC is known to play a critical role in goal-directed behavior
What systems?
DA in the striatum (Nuclues accumbens - NAc) and midbrain (VTA).
Reward occurrence, prediction, omission
DA pathway
- Glu
- GABA
- Mesolimbic DA
- Mesocrtical DA
- Nigrostriatal DA
Ritalin administration during PET
Revealed a correlation between the dose of medication and the occupancy of the DA transporter (blocking DA reuptake)
Social rank and DA in monkeys
Greater DA D2 receptors in the striatum in dominant monkeys (higher social hierarchy).
Administered less cocaine.
Provides some insight into the correlation between increased substance abuse and lower socioeconomic status!
Wanting VS Liking
DA is more wanting in addictions. Not the pleasurable experience, but rather fulfilling the easement feeling
Amygdala & Reward
It’s essential to remembering the rewarding associations
Classical conditioning
A rat without an amygdala will fail to resume pressing the level when stimulated with the tone or light
Reward and Time
Studies have shown that D2 agonists accelerate the internal clock
Utilization of DA and to some extent activate the VTA
Reward Pathway
The dopaminergic pathway mostly involved in reward is the so-called mesolimbic system, which is formed by projections of midbrain dopamine neurons of the ventral tegmental area (VTA) to the striatum, prefrontal cortex, amygdala, hippocampus, and many other structures of the limbic system.
What is addiction?
The continued pursuit of a substance to activity in spite of negative consequences.
Drugs of abuse overwhelm and fundamentally alter the neurons that were never intended to experience such supra-physiological levels of neurotransmitters.
Location of several commonly abused drugs 1
- meso-limbic, and even indirectly to it
- blockage of DA reuptake pump (y3ne more DA available to stimulate NAc (nucleus accumbens)
Location of several commonly abused drugs 2
VTA —> DA —> NAc —> PFC
VTA: Nicotine and alcohol. GABA through Opiates.
NAc: Stimulants. Endorphin pathways through Nicotine and alcohol.
PFC: Glutamate through PCP
Clinical manifestations of addiction
- Tolerance and withdrawal
- Depression and anhedonia when not using
- Less responsive to natural rewards
- The capacity to relapse when many years after abstinence
