Neuromodulators/
Interneurons
Neurons that can affect the activity in entire brain regions rather than just a single synapse
- -> alter/modulate how neurons transmit + receive signals
- -> many diseases that affect learning + memory involve a decline in neuromodulators
ex.: Alzheimers –> reduction in acetylcholine
Synaptic plasticity
The ability of synapses to change as a result of experience
–> learning involves a strengthening/weakening of connections between neurons
Hebbian learning
Two cells that send impulses simultaneously to the same region, will tend to make connections to intermediate cells in common, then no longer act independently
–> the repeated stimulus will thus be more likely to be recognized
“Neurons that fire together, wire together”
How will Hebbian learning help, if one encounters an incomplete version of a familiar stimulus ?
The connections already established through repeated experiences will produce outputs that complete the familiar pattern
Long term potentiation
LTP
Refers to the effect when a synaptic transmission becomes MORE effective as a result of recent activity
–> changes can last for hours/days
Long term depression
LTD
Occurs when synaptic transmission becomes LESS effective as a result of recent activity
- -> connections between neurons that don’t fire together weaken
- -> opposite to LTP
Cell assemblies
Hebb
Refer to large groups of cells that tend to be active at the same time because they have been activated simultaneously in the past
–> can encode many different memories with each neuron participating to a greater or lesser extent in a particular memory
Which synaptic changes occur to store memories ?
- Training results in an increased release of neurotransmitter molecules
- Increased size of PSP
- Postsynaptic membrane will have a larger response to same amount of NT release, due to its bigger size
- Neural circuit increases the number of synaptic contacts
- More frequently used synapses survive, less used die
Hebbian synapses
Refers to a synapse that uses a time-dependent, highly local, and strongly interactive mechanism to increase synaptic efficacy
Dual trace hypothesis
Hebb
Formation of a memory involves a brief, transient process:
- Experience sets up activity that reverberates through the activated neural circuits (STM)
- -> held for a short period - If sufficient, this activity will lead to stable changes in NS (LTM)
Which were the 3 most common laboratory environments for experiments ?
- Standard condition (SC)
- -> 3 animals kept in stand. laboratory w/ food + water - Impoverished/Isolated condition (IC)
- -> 1 animal kept in SC-sized cage - Enriched condition (EC)
- -> 10-12 animals kept in large cage containing a variety of stimulus objects, changed daily
Which cognitive results did the brains of the animals kept in the EC yield ?
- Greater activity of the enzyme acetylcholine
- Thicker cerebral cortices
- Alteration of the expression of a large number of genes
- -> may play important roles in learning + memory - Increase in synaptic connections + more elaborate information processing circuits
Where is memory stored ?
Where is information processed for memory storage ?
Stored: Cerebral cortex
Processed: Other brain regions (Hippocampus etc)
Process of the induction of LTP
- Glutamate is released at synapse that has AMPA + NDMA receptors
- Stimulation will first only activate AMPA receptors
- -> NMDA don’t respond, due to blockage of Mg ions - Sufficient activation of AMPA receptors in same neuron will partially depolarize the membrane, removing Mg+ block
- NDMA receptors now actively respond to glutamate, thus admit large amounts of Ca+
- Protein kinases are activated as a result, which change the properties of many proteins
- CaMs increase the number of AMPA receptors on PS site
–> Membrane will give a larger response to the same weak signal
Portein kinases
Enzymes that catalyze phosphorylation
–> blockage of the kinases can prevent the induction of LTP
(Ca-calmodulin (CaM), Protein kinase a/c)
Phosphorylation
Adding the element phosphor to an organic molecule
–> changes the properties of the molecule
Calcium-Calmodulin kinase
CaM
Remains active once it is put into that state by Ca2+, even if the level of Ca2+ falls
–> plays a main role in maintaining LTP
In which ways does CaM affect AMPA receptors ?
- Increases the conductance of AMPA receptors already present in the membrane
- Promotes the movement of the AMPA receptors from the interior of the spine into the membrane
–> more receptors are available to stimulate the spine
Immediate early genes
IEGs
Refer to a class of genes that are rapidly but transiently expressed in response to extracellular signals
–> are expressed within min
ex.: neurotransmitters, NGFs
CREB
Its activation leads to an increase in the expression of IEGs, due to transcription
–> Transcription factor
Steps in the neurochemical cascade during the induction of LTP
- Increase in intracellular Ca2+
- Activation of protein kinases, which phosphorylate proteins
- Activated kinases bind to CREB
- IEGs enter nucleus, + regulate the expression of LEGs
- Transcription of LEGs leads to synthesis of proteins
- -> necessary to induce LTP - Proteins are then transported down the axon to alter the response of the neuron to further stimuli
Late effector genes
LEGs
Genes that are transcribed to produce proteins necessary for the induction of LTP
–> are expressed within hours
Why is Calcium so important in cellular consolidation ?
- Facilitates processes that can help with the insertion of additional AMPA receptors (Postsyn. membrane)
- Changes the efficiency of exocytosis of glutamate vesicles (Presyn. membrane)
What needs to happen for a memory trace to be long lasting + stable ?
A condition in which 2 cells are coactivated multiple times needs to be created
–> increase in synaptic strength, which will be permanent
