Lecture 26- Reward Dysfunction Flashcards
What two types of brain systems are there?
-Systems with a specific function: For example, the visual system or the system invovled in fine movements of the fingers
-Systems with a generic function: systems that process information received
from regions performing widely differing specific functions to perform a particular behaviourally important operation (you can’t easily say where the operation/ function is located: is kind of spilt across lots of different regions).
What is the mesolimbic dopamine (ventral) circuit as part of the reward system?
- Inputs from hippocampus to integrate memory of ‘context’
- Inputs from amygdala to
integrate memory
of an emotional e.g.
fearful situation
What is the nigrostriatal
dopamine (dorsal) circuit as part of the reward system?
- Reinforces sensory-motor
associations - Important in learning new skills
- Important in forming habits: also disordered in addictions
What type of system is the reward system (specific or generic)?
It is a generic system because it integrates information from many addiction areas serving different functions and SELECTS a behavioural response: e.g. stay or go?; repeat what you just did or don’t; or do something different.
What group of brain structures does the reward system often involve?
Basal Ganglia
Which components of the basal ganglia are associated with either the mesolimbic dopamine circuit or the nigrostriatal dopamine (sensorimotor) circuit?
1)
Striatum (caudate,
putamen- sensorimotor- dorsal circuit).
Nucleus accumbens
(limbic- ventral)
2) Globus pallidus
(sensorimotor-dorsal), ventral pallidum (limbic-ventral)
3) Substantia nigra
(sensorimotor dopamine -
nigrostriatal-dorsal), ventral
tegmental area (limbic
dopamine - mesolimbic- ventral)
4) (Subthalamic nucleus)
How does the basal ganglia part of the reward system
select between the options of what to do? What is the problem with this?
-There are separate pathways that lead to different behavioural outputs
-We have competing
‘motivations’ BUT only
one set of muscles to
respond with! So need to ensure correct ‘selection’
-This selection is the role of the reward system in the basal ganglia. Different parts select the most appropriate
/ most important movement, sensation, idea, plan, memory, emotion, in a given situation, based on experience
What different actions/ paths can the reward system follow in order to choose the best outcome?
-Limbic areas= Motivation/emotion
-Associative/ sensory areas= Cognition (ideas/memories/plans)
-Motor areas= responsible for sensorimotor (stimuli/ actions)
What tool do the basal ganglia use to inform choice actions? (think a psychology concept)
Reinforcement learning –
learning the strategy to be taken in a given situation that maximises the
chance of a successful outcome
-strategy is stored for later selection
-reinforcement makes that strategy more likely to be selected in a similar situation in future
How is dopamine important in reinforcement learning?
positive reinforcement releases dopamine and therefore, increases the chance of action again (want dopamine release to happen again). I.e. dopamine is essential for learning.
Where can the dopamine signal (or the amount of dopamine released after a rewarding stimuli) be measured? What might these rewarding stimuli be?
-In the striatum of the basal ganglia
-Rewarding stimuli= sex/ food
When does dopamine need to be released in order to be reinforcing and what change to the synapses occurs?
-Release of dopamine into the striatum AFTER cortical activity (an ‘action’) can increase the strength of synapses from the cortex
-Temporal order is important: has to be after otherwise it doesn’t make sense not backing up the action so won’t be reinforced to do it again.
-Therefore, Synaptic plasticity at corticostriatal synapses controls what is learnt for later selection
How do you record the strength of the corticostriatal synapses?
Record via an electrode into the spiny projection neurons which connect to the cortical neurons
What physiological term describes the strengthening of the corticostriatal synapses in response to positively rewarding stimuli after a cortical action (reinforcement/ reward learning)?
Long Term Potentiation (LTP)
How do we know that dopamine release is reinforcing?
-Because animals will learn the action required to activate their own dopamine pathways: Intracranial self-stimulation (ICSS)
-ICSS is where a stimulating electrode is placed in an area near dopamine neurons (near the substania nigra) . The animal will just keep pressing the lever to release more dopamine (it has directly activated the reward pathways).
