Memory consolidation

Question 1

Describe the first experiment that led to the idea that memory consolidation occurs during sleep [6]

Answer 1

• place cell firing recorded as mouse rune through maze
• used to determine the sequential activation of the place cells in the hippocampus
• when mouse left to sleep
• place cells were reactivated
• and fired in the sequence as when awake
• occurs on a compressed timescale (seconds to ms)

Question 2

What was special about the timescale of reactivity of these place cells in memory consolidation experiment

Answer 2

ideal for synaptic plasticity

Question 3

When do the ‘replay events’ occur

Answer 3

slow wave sleep SWR

Question 4

Describe the relation between hippocampus and PFC to replay events. include evidence [3]

Answer 4

• recorded neuronal activity in PFC and HPC as rat explored maze
• recorded replay events during sleep/rest
• timing of reactivation PFC relative to HOC same as doing exploration

Question 5

What other areas have similar findings been found to have replay events [2]

Answer 5

• entorhinal cortex
• visual cortex

Question 6

What is the current role of rest and sleep in memory consolidation [2]

Answer 6

• rest: offline activation of HPC-cortical cell assemblies
• sleep: enables LTM consolidation

Question 7

Who was HM [3]

Answer 7

• brain areas removed due to epilepsy
• unable to form declarative memories
• could remember early childhood

Question 8

The association areas stores LTM while HPC involved in encoding new memories. Describe a hypothesis related to this [3]

Answer 8

• HPC works with cortex to create new memories
• gradual plasticity process (with HPC) connection between neurones and cortical regions are strengthened
• until memory can be accessed independently of HPC

Question 9

What are slow oscillations [5]

Answer 9

• low frequency waves ~1Hz
• occur during nREM sleep
• coincide with period of high neuronal activity (depolarisation: up states)
• and low neuronal activity (hyperpolarisation: down states)
• occur as ripples from rostral(front) to caudal areas of the brain

Question 10

What are spindle oscillations [2]

Answer 10

• occur in non REM sleep
• brief bursts of activity 9-16Hz

Question 11

What is the difference between spindle oscillation and SWR

Answer 11

spindle oscillations are shorter than SWR

Question 12

Identify the stages of sleep and key features [4]

Answer 12

REM
- stage R (dreaming)
NREM
- stage N1 (light sleep)
- stage N2 (deep sleep)
- stage N3 (deep sleep, sleep walking)

Question 13

How would you expect a hynogram in the early hours of sleep differ to the later hours of sleep in a healthy adult [2]

Answer 13

• more deep sleep in early cycles of sleep
• more REM in the later sleep cycles

Question 14

Identify the physiological features of REM sleep [3]

Answer 14

• large eye saccades (eyes flick)
• lose muscle tone (except eyes)

Question 15

What type of brain waves are seen in light sleep [1]

Answer 15

theta (4-7Hz)

Question 16

What stage of sleep are slow oscillations most commonly found

Answer 16

N3 (deep sleep)

Question 17

What stage of sleep are spindle oscillation most commonly found

Answer 17

N2 (deep sleep)

Question 18

How does the sleep architecture differ in rodents vs primates [2]

Answer 18

• rodents do not have stint stages of NREM
• have higher frequencies theta waves in REM sleep

Question 19

What evidence is there for consolidation theory [3]

Answer 19

• cortical ECoG and HPC LFP recordings taken in epilepsy patients
• found that spindles occur at same time as slow oscillations in up states
• hippocampal ripples coincident with troughs of cortical spindles

Question 20

What is the novel object task [3]

Answer 20

• mouse explores where there are two objects in initial exploration
• then move the location of one of the object
• if memory intact mouse will go to object that has moved location out of interest

Question 21

Describe the experiment that showed slow oscillations - spindle - ripple coupling supports memory consolidation [4]

Answer 21

• electrodes in HPC and PFC
• HPC ripples detected in real time
• when there were HPC ripples mPFC was simulated to evoke low oscillations they were followed by spindles
• mouse did better in novel object task

Question 22

Describe evidence that slow oscillations and spindles modulate neuronal activity [2]

Answer 22

• imaged the activity of different neuronal subtypes during sleep
• when there were concurrent SO and spindles there were also bursts of neuronal activity in cells

Question 23

How SO associated with excitatory pyramidal neurones

Answer 23

increases activation

Question 24

How are SO associated with PV+ neurones

Answer 24

increased activation

Question 25

How are SO associated with inhibitory SOM+ neurones

Answer 25

deceased activation

Question 26

What evidence is there that spindles are associated with increased dendritic activity [3]

Answer 26

- increased dendritic Ca2+ activity - same as measuring spindle activity - when traces overlapped there is a strong correlation between two (well aligned)

Question 27

Explain how the effect of PV+, pyramidal cells and SOM+ cells are involved in memory consolidation [5]

Answer 27

- neurones from cortex and hippocampus excite pyramidal dendrites (replay events) - increases activity of PV cells - SOM activity is decreased by increased PV activity - which disinhibits dendrite of pyramidal cells - increases pyramidal cell activation

Question 28

How do spindle oscillation aid synaptic plasticity [2]

Answer 28

- create brief periods od dendritic depolarisation in cortical neurones - priming them to undergo synaptic plasticity