24.5 Memory

Question 1

Describe the paradox of where memory is stored in the brain

Answer 1

Memory is both distributed and localised

Distributed - many parts of NS represent a single event
Localised - a single event involves a limited number of brain systems

Question 2

What is the root cause of Korsakoff syndrome?

Answer 2

Thiamine (vit B1) deficiency

Question 3

What is the common cause of Korsakoff syndrome?

Answer 3

Alcohol misuse

Question 4

What are the characteristics of Korsakoff syndrome?

Answer 4

• Problems learning new info
• Cannot remember recent events
• Long-term memory gaps

Question 5

What is the one-line summary of the Hebbian synapse?

Answer 5

Cells that fire together wire together

Question 6

Describe the plasticity of Hebb synapses shown from a) and b) to c) in the diagram (shows optic neurons from each eye going into a cat LGN)

Answer 6

(a, b) Initially the synapses to the LGN overlap. Neurons from top or bottom eye fire simultaneously to cause top or bottom LGN neuron to fire.

(c) Over time, the neurons that fire together wire together. Note opposite also happens: Input cells that fire out of time with the target lose their link.

Question 7

What is the general structure of the hippocampus?

Answer 7

Two thin sheets of neurons folded onto each other

Question 8

What are the two layers of the hippocampus called?

Answer 8

Dentate gyrus and hippocampus proper (Ammon’s horn)

Question 9

What are the four subdivisions of the hippocampus proper (Ammon’s horn)?

Answer 9

CA1, CA2, CA3, CA4

Question 10

Which of the subdivisions of the hippocampus are involved in long-term potentiation (LTP) of declarative memory?

Answer 10

CA1, CA3

Question 11

What is the difference between declarative and non-declarative memory?

Answer 11

Declarative memory = conscious memory of facts/knowledge
Non-declarative = unconscious memory through e.g. skills, conditioning

Question 12

Which specific types of memory is LTP involved in (according to the spec)?

Answer 12

Spatial (locations, route to locations)
Episodic (temporary memory, e.g. what you had for breakfast)

Question 13

What provides the major input into the hippocampus?

Answer 13

Entorhinal cortex

Question 14

Entorhinal cortex provides input that synapses onto the…

Answer 14

dentate gyrus

Question 15

Dentate gyrus sends mossy fibres to…

Answer 15

CA3 pyramidal neurons

Question 16

CA3 pyramidal neurons sends one axon to the fornix (irrelevant to memory) and one axon to…? What are these axons called?

Answer 16

CA1 neurons
Axons = Schaffer collaterals

Question 17

Describe how LTP occurs in a CA1 neuron in terms of the firing frequency mechanism.

Answer 17

Schaffer collaterals need to fire a high-frequency train of stimuli (tetanus) to the CA1 neurons
This evokes a long-lasting increase in EPSP amplitude, as synapses made more effective
= LTP

Question 18

Describe how LTP can occur with the Hebbian synapse mechanism.

Answer 18

‘Cells that fire together wire together’

• When two CA3 Schaffer inputs (input 1 and 2) fire at the same time - bc of spatial summation, they cause the postsynaptic CA1 neuron to fire, causing LTP
• Now EITHER input 1 OR 2 can fire on their own to cause CA1 neuron to fire
  –> Association formed between input 1 and 2 (e.g. association between a duck and a quack sound)

Question 19

What are the two requirements for LTP to occur?

Answer 19

1) Synapses are stimulated at frequencies high enough to cause temporal summation of the EPSPs
2) Enough synapses must be active simultaneously to cause significant spatial summation of EPSPs