11 Learning and memory

declarative = conscious

—> semantic/episodic memory

—> Medial temporal lobes (Hippocampus, Rhinocortex), Diencephalon, saved in neocortex

non-declarative = unconscious

—> procedural memory, (non)/associative memory

—> Striatum, Cerebellum, Amygdala, Reflex arcs

• Fear memory = amygdala

• Reward memory = nucleus accumbens

—> associative learning

= non-associative learning

habituation = learning to ignore a stimulus that lacks meaning

—> Decreased response to a repeated harmless stimulus

• voltage gated Ca2+-channels are insufficient

• between sensory and motor neurons less neurotransmitter release

sensitization = learning to intensify the response to a stimuli

—> Increased response to a stimulus

• Interneuron —> serotonin —> presynapse of the sensory neuron —> GPR —> AC —> cAMP —> PKA —> voltage gated Ca2+-channels are open longer

• activates transcription activator CREB —> gene regulation

sea slug with only 20 000 neurons and large nerve cells

—> model for learning and memory research

molecular mechanisms of

• habituation

• sensitization

associative learning

classical conditioning (linked to sensitization learning processes)

= one stimulus predicts another

1. Before learning: NS → no response; US → UR

2. During learning: NS + US → UR (repeated pairing)

   NS —> CS

3. After learning: CS (+ without US) → CR

—> Pairing NS and US activates the cAMP/PKA pathway via a dually regulated adenylyl cyclase, strengthens the synapse + transcription factor CREB

instrumental conditioning (linked to habituation)

= behavior-associated

motor response is linked to a reward (rat presses button and gets food)

—> dopaminergic response in Striatum —> habits

instrumental conditioning → habit formation → procedural memory (striatum)

= procedural learning

• fear conditioning = associative learning

• fear memory in the amygdala

molecular mechanisms

• Inhibitory Avoidance

• LTP in the Hippocampus —> NMDA Receptors

• Protein Synthesis for short —> long-term (= consilidation)

= declarative memory

neuronal assemblies

LTP = Neurons that fire together, wire together

• long-lasting reinforcement of synaptic transmission between neurons

• NMDA receptors

  • have to bind Glutamate

  • lost their Mg block because of the depolarisation through AMPA receptors

• increase of AMPA receptors —> stronger synapses —> cell is more sensitive to Glutamate

<-> LTD: long-term-depression

• weak depolarization

• Magnesium block in the NMDA channel is only partially resolved —> Degradation of AMPA receptors —> weaker synpases

strengthened synapses = engram

distributed over many cell contacts in a neuronal assembly

• Partial damage ≠ complete loss of memory

• Partial activation = recall

= Sensory ultrashort memory, raw data

—> just a small fraction goes into our working/short-term memory

• high storage capacity

• unfiltered information

• 2 memories

  • visual sensory memory = iconografic memory

  • auditive sensory memory = echoic memory

    
    

we have to pay attention

7±2 items

e.g. single numbers = memory span

over 9 = exceed older items will be lost

Chunking = grouping information into meaningful units

working memory = immediate use

short-term memory = retains information for a longer period of time (hours) with the potential of consilidation

can be erased due to trauma/electric shock

retrograde amnesia: no memory what happened before the trauma

anterograde amnesia: no memory built after trauma

retrograde amnesia, anterograde amnesia because of alcohol abuse

= long term memory (days-years)

classical model

hippocampus —> synaptic plasticity/LTP/Proteinsynthesis/trancription factor CREB —> transition to long time memory cells —> stored in Neocortex

<-> Multiple trace model as alternative

Hippocampus remains involved in episodic memories

—> new “traces” are formed between the hippocampus and the neocortex each time a memory is retrieved

classical model:

• when hippocampus misses out (patient HM), no new memories can be stored

Multiple trace model:

• episodic memory depends on Hippocampus

sensory register

• seconds, automatically

working memory

• 7±2 items

short term memory

• consilidation (repeats) needed

long term memory

• LTD

—> when reactivated (recalled) —> "labile"/unstable

—> memory can be weakened, erased, or altered before it is reconsolidated

Hippocampus → Fornix → Mammilary bodies (Nuclei of Hypothalamus) → Tractus mamillothalamicus → nuclei of anterior Thalamus → Gyrus cinguli → entorhinaler Cortex → Hippocampus

• entorhinal cortex

• parahippocampal cortex

• cortical association areas

• fornix

personality, language, intelligence stayed normal

= Inability to transfer new information from short-term/working memory to long-term memory (consolidation failure)

place cells = Hippocampus: specific location “What happens where”

grid cells = entrhinal cortex: numeroud locations (metric) = “Where”

—> grid cells may activate place cells