Learning/Memory and Reward, dopamine, and addiction Flashcards
learning
process of encoding new information
memory
the newly encoded information ⇒ formalizing with physiological and biological change
- Can be stored/present in the brain across short seconds to long years over timescales
- The expression of learned memories allows for new behavior, decision making, and adaptation
long term potentiation (LTP)
strengthening of synaptic connections (potentiation) as a consequence of repeated activation
- Cells that fire together wire together
- Initially discovered in rabbit hippocampus
what does balance of synaptic strengthening/weakening across brain regions reflect?
the storage and decay of information during learning and forgetting
what is memory consolidation necessary for? When does it happen?
stability; sleep
what does LTP stimulate?
an input neuron and get output activity
components of LTP? (5)
- LTP is a change in the baseline strength of a synaptic connection
- Durability depends on how the stimulus is induced ⇒ most often it is not permanent for a given synapse
- The collective cells underlie learning
- There are also depressions across synapses after the experience
- You can demonstrate an increase in the connection strength
how does repeated activation change neurons? (3)
- morphology
- membrane receptor makeup and concentration
- gene expression
how does morphology change from repeated activity of neurons?
If the protrusions change in shape/multiply at the synapse this can change morphology of neurons in striatum
what does morphology refer to?
dendritic spines/synaptic contact points
how does membrane receptor makeup and concentration change from repeated activation?
The pre learning state has less vesicles and less receptors but after LTP both are increased
- Neurotransmitter release
- Neurotransmitter receptors
how does gene expression change from repeated neural activation?
epigenetics or gene alterations
Non-declarative/Procedural memory
automatic, motor, and skill based learning ⇒ sequences of action we engage in a lot
- Also things with background associations such as pavlovian
Nondeclarative types of memory (3)
- Skills and habits ⇒ basal ganglia, cerebellum, neocortex
- Emotional associations ⇒ amygdala
- Adjusting reflexes ⇒ cerebellum
declarative memory
what and where memories that are explicit ⇒ encyclopedia information
types of declarative memory?
- episodic
- semantic
episodic memory
remembering events
- Autobiographical
- Spatial
semantic memory
knowing facts
what lobe is involved in declarative memory?
the medial temporal lobe
associative learning
pavlovian conditioning and operant conditions results in non declarative or implicit memories
- Forming unconscious associations and expectations about the world
- Procedural memories ⇒ motor plans and skills
HM
treated for temporal lobe epilepsy with a bilateral lesion of part of his medial temporal lobe
- removal/disconnection of the hippocampus and amygdala
what happened after HM’s surgery?
He was unable to form new declarative memories after ⇒ facts, events, people
which memories were intact after HM’s surgery?
Procedural memories were intact (aka motor memories)
what happens when people without declarative memory are repeatedly asked to draw a star?
- The same people can do a procedural task where they draw lines between the two stars and stay in between the lines
- After multiple days of working on this they get better at it even though they don’t remember doing it prior
what brain regions are involved in procedural memory?
cortex, basal ganglia, thalamus loop
what type of phenomenon does procedural memory allow? (3)
Associative learning, motor skills, habits
- damage impairs motor control and skill learning
Huntington; what don’t they have deficits in?
medium spiny neurons die off in the striatum and people often have motor impairments
- Happens progressively based on striatal damage
- Don’t have deficits in declarative memories
medial temporal lobe damage results
leads to disruption of declarative and emotional memory formation
Hippocampus
“C” shaped that wraps around the thalamus and has an output track called the fornix
Papez circuit
responsible for declarative memory formation
- Hippocampus ⇒ fornix tract ⇒ mammillary bodies ⇒ mammillothalamic tract ⇒ anterior thalamus ⇒ cingulate gyrus ⇒ hippocampus
what does the hippocampus give us in terms of information?
the what and where of information
spatial memory cells (2)
- place cells
- grid cells
place cells
where specific location encoding is done by individual neurons in the hippocampus ⇒ fire at a specific location
grid cells
spatial geometry encoding by individual neurons in entorhinal cortex
- represented by action potentials for a single grid cell based on space
how does the hippocampus reflect where you are in space?
they change the activity of neurons
amygdala
key for linking emotional experience to events during memory formation
where does memory formation generally occur?
largely in subcortical structures
where does memory storage generally occur?
distributed across cortical areas
what does the frontal cortex encode?
episodic/semantic
what does the motor cortex and cerebellum encode?
procedural
what do sensory specific cortices and association cortices encode?
audio or visual memory
T/F the medial temporal lobe is where memories are long term stored?
no, we know this from HM
reward circuit
direct behavior toward advantageous stimuli
- promote future acquisition
examples of reward circuits
Food, sex, exercise, social interaction ⇒ evolutionarily advantageous that we seek out for survival
what are reward circuits important for? (3)
- signaling value of rewards
- directing learning about them
- producing the motivation to obtain them
how are rewards experienced?
as positive emotions
what are negative effects of reward circuits?
can also produce disadvantageous reward seeking behavior, as happens in addiction
major brain regions that control reward seeking and are affected by drugs (2)
- basal ganglia
- limbic system
what parts of the basal ganglia are involved in reward seeking (2- structure and neurotransmitter)
dopamine, striatum
what parts of the limbic system are involved in reward seeking (4)
prefrontal cortex, amygdala, insula, hippocampus
what areas of dopamine neuron cell bodies are in the midbrain? (2)
- substantia nigra pars comopacta
- ventral tegmental area
what pathway is involved with the substantia nigra pars compacta?
nigrostriatal pathway
- Motor systems, control of movement, etc.
- projects to striatum
what are the pathways of the ventral tegmental area?
- mesostriatal/mesolimbic pathway
- mesocortical pathway
what does the mesostriatal/mesolimbic pathway do?
engaged during reward related behaviors
- projects to the nucleus accumbens
what does the mesocortical pathway do?
project to frontal and nucleus accumbens
- Make and release dopamine but project to different parts of the forebrain in prefrontal area
what do all parts of the striatum receive?
strong axon inputs from dopamine neurons located in the different parts of the midbrain
where are dopamine neurons concentrated? Where do they project to?
SNc; dorsal striatum (caudate/putamen) and VTA
- from there they project to the nucleus accumbent to make a W shape
Brain stimulation reward (BSR)
animals will work very hard to receive electrical stimulation of certain brain regions
- You can stimulate certain parts of the brain to demonstrate it will create a value of a reward signal
what species was BSR done with?
with mice by implanting a stimulation device and animals will work really hard to get stimulation delivered to parts of the brain
- the rat learned that if it presses the bar there will be a zap of stimulation into its brain via the electrode placed there
- this is possible for feelings of reward when we engage in experiences
what regions support BSR? (5)
- VTA/SNc
- Medial forebrain bundle
- Septum
- PFC
- Striatum
what brain areas support the strongest reward?
VTA and medial forebrain area
what dampens BSR and blunts reward seeking?
dopamine neuron lesions or pharmacological inactivation of dopamine signaling
- these studies established that dopamine is critical for a core feature of behavior ⇒ positive reinforcement
Rewarding stimuli
things that feel good and are wanted
- Stimulate dopamine release in the nucleus accumbens and striatum
- Eating, sex, exercise, social activities, etc.
- This signal is needed for learning and motivational drive for survival, but is co-opted by drugs
how do drugs compare to normal rewards?
most drugs produce much greater dopamine levels, compared to food rewards ⇒ have an impact on the brain that promote things non-essential for survival
- drug effects extend longer over time than food which engaged neuronal mechanisms even more
T/F all drugs increase dopamine signaling?
(T) drug classes/types like stimulants vs opioids have the same effect
- Increase dopamine signaling in the striatum
- Like natural rewards of different modalities, these classes also increase dopamine
what does drug exposure do to genes?
rapidly alters gene expression in reward systems
- May change expression in reward circuits ⇒ increase or reduce
what happens with drug tolerance?
chronic administration creates tolerance for what that drug does
- Often other parts are sensitized
- The two things can happen at once => This is what makes addiction cycles viscous
what does repeated drug exposure do to the dopamine system?
they sensitize and overactivate reward systems
- The same experience promotes a greater response in the brain than it does originally
what does drug exposure do to stratal neuron structure?
by increasing the density and thickness of the spines on the neurons, the synaptic connectivity is stronger and signaling at the synapses is stronger
- changes the physical makeup
T/F drugs damage brain tissue?
most drug use does not damage brain tissue, but produces changes in gene expression, morphology, and neurotransmission that affect learning, decision making, and motivation
how does sucrose compare to amphetamine?
sucrose has much less of a plasticity increase as amphetamine does
- Shows the drugs activate things in an exaggerated way
addiction
a medical condition, based on drug effects on brain systems that support normal reward seeking and motivation
- Continued drug use despite negative consequences
- Persistent drug craving and compulsive use
- Relapse
