Lecture 3 Flashcards
What are the resting state networks and the default mode network – what can they tell us about brain activity how can they be examined? (lecture 3)
pC, mPFC and bIPR monitoring in —– of an explicity task the —— and ——- environment
DMN discovered via — most commonly measured by___ why?
DMN is _______ as sleep depth Inc - may relate to _ _ _
DMN linked with mood and cog - may underlie why we experience fluctuations in mood and cognitive ability if we have SD
mPFC of DMN shows more connecitivty to the rest of the DMN in people who slept more over course of 2 weeks
DMN can be examined using MEG - magnetic fields are less disrupted than EEG by skull or other tissues.
Asymetric acitivty in the first night being measured, keeps you safe (more viglant) second night don’t get this activity
RSN
- RSN are a series of functionally connected networks that can be identified with fMRI – within a network activity increases and decreases coherently,
- Regions form a network in that they preferentially communicate with each other
- Can be seen in the absence of task completion
DMN
set of regions that reduced their brain activity during a task
Posterior cingulate/precuneus, medial prefrontal and bilateral inferior parietal regions monitoring the internal and external environment in the absence of an explicit task
- DMN was discovered via PET
- most commonly measured using fMRI due to the advantages – less invasive, no tracer injected.
- Generally, DMN activity and connectivity is reduced as sleep depth increases. May relate to a loss of consciousness.
- The frontal part (mPFC) of the DMN shows more connectivity to the rest of the DMN in people who slept more over the course of 2 weeks (cumulative total sleep time). As the DMN is linked with changes in mood and cognition, this may underlie why we often experience fluctuations in mood and cognitive ability if we have sleep deprivation.
- DMN can be examined using MEG – Magnetoencephalography. Magnetic fields are less disrupted than EEG by skull and other tissues of brain. In first night of sleep in unfamiliar environment, SWA in DMN is asymmetric – one hemisphere kept more vigilant? Downside is poorer sleep, upside is you’re safer. In second night, you don’t get this asymmetric activity as much.
How do sleep spindles influence memory consolidation
Cause a massive influx of calcium into pyramidal cells of cerebral cortex this triggers intracellular calcium-dependent mechanisms required for synaptic plasticity
What are sleep discharges?
electrophysiological activity that is very specific and defines the sleep cycle. They are generated by the cortex – influenced by the thalamus
What did Clemens et al (2005) find when he conducted a study asking 19 participants to remember 10 f___and their associated n____ to be recalled ______ and _______ sleep
overall memory retention correlated with number of sleep spindles 12/19 improved memory performance after sleep Verbal memory retention correlated with nubmer of spindles at left fronto-central electrodes No correlation with TST or specifc stages Specifically SS related to memory consolidation
The functional role of spindle activity is generally not clarified but describe the evidence that sleep spindles have been linked with memory consolidation, learning and sleep stability
Clemens et al (2005) It is specifically number of sleep spindles that related to memory consolidation Hennies et al (2016) ss relate to interaction between new and exisiting knowledge Dang-Vu et al () Sleep spindes serve a sleep protective function
Give three examples of Sleep discharges
Vertex sharp waves (N1) SLeep spindles and K complexes (N2) Delta slow wave activity (N3)
What did Hennies et al (2016) find in their study of categorising insects?
How do their findings support the dual process model
(reduction hipp)
SS related to interaction between new and existing knowledge new schema learnt over two weeks then new facts (schema-related or not)
presented with new images of insects had to fit them in SSs were associated with intergration of new knoweldge and pre-defined existing knowledge:
- SS predicted:
- increase in schema-benefit over retention period and decay of schema related memories
- a reduction of hippocampus fMRI activation for remote vs recent schema-related facts
- (suggesting support for the dual-process model of sleep hippocampus neocortical transfer)
Dang- Vu et al study of sounds of increasing intensity
SS serve a sleep-portection sounds of increaseing intensity to sleeping participants Ppts with more sleep spindles in quiet night were more difficult to arouse in noisy night ss may be invovled in montior the outside world and prevent you from waking to every external stimulus
Thalamus
when TC neurons are ———- thalamic and cortical neurons become ———- and fire in an O——– M—— independent of E——– S———-
Changes in neuromodulatory environment modify TC –> s_______ E_ a_____ i_ d_________ s____
The effect o sleep on the T——— can be investigated with E–/f—
Hale et al (2016) increase in TFC as go into –
Involved in spindle creation
associated with b—– f——- in the t———c——– p——–
inhibited
synchronous
oscillatory mode
external stimulus
specific EEG activity in different stages
THe effect of sleep on the thalamus can be investigated ith EEG/fMRI
Hale et al (2016) increase in thalamocortical functional connectivity as go into N2 that is that it becomes a more homogenous structure
spindle creation
associated with burst firing in the thalamocortical populations and arise from cyclic inhibition of thalamocortical neurons by reticular thalamic neurons this entrains cortical populations in spindle oscillations
relays infoation to the cortex
all sensory input from the periphery goes ot the lamamus on its way to the cortex
regulating sleep onset
wakefulness signals interupted by the thalamus it serves as gatekeeper to the cerbral cortex effectively dissconneticing the cortex from most internal andexternal signals
During NREM the TRN inhibits TC neruons inhibiting infotransfer
when TC neurons inhibited thalamic and cortical neruons become synchronsied and ffire in an osscillatory model independent of external stimuli
THe effect of sleep on the thalamus can be investigated with EEG/fMRI
Hale et al (2016) inrease in thalmocortical functional connectivity s go into N2 - thalamus becomes a > homogenous strucure
Fatal Familial Insomnia (FFI)
malformed proteins called prions attach the suffer’s thalamus - makes sleep impossible
What are the main techniques that can be used to investigate the brain during sleep, and what are their advantages and disadvantages? (S)
PSG
Nuclear Imaging (PET, SPECT) MEG
fMRI
what is psg?
How does it work?
what output does it give?
- Gamma – stimulated high energy >–Hz
- Beta – aroused, attentive – ~ –Hz
- Alpha – relaxed - ~ –Hz
- Theta – drowsy - ~ - Hz
- Delta – sleep (N3) -.- ~ -Hz
PSG stands for Polysomnography. In its simplest form, it is the combination of EOG, EMG and EEG
other physiological variables can be measured: nasal pressure and airflow to diagnose breathing-related sleep disorders such as OSA
American Academy of Sleep Guidelines recommend:
- 6 channels of EEG – plus a mastoid reference. Pioneered by Berger in 1930.
- 2 channels of EOG – 1 cm below left and 1 below right outer canthus (corner of eye)
- 3 channels of EMG – midline
- 1 cm above inferior edge of mandible
- 2cm below inferior edge and 2 cm to right of midline and another 2 cm to left
- 10/20 system used to standardize where to put electrodes, from iniam (base of skull) to nasian (top of nose). Want to be putting them in same places on different people’s heads, so head size is measured from nasion to inion, and also measurements from ear to ear.
- There are frontal, temporal, occipital and parietal nodes
- PSG should be as minimally invasive as possible so people’s sleep is as undisturbed as possible
HOW The scalp signal –
- synchronised postsynaptic potentials of large neural (pyramidal cell populations) – NOT APs. Measured via an array of electrodes arranged on the head systematically, voltage difference measured against a chosen reference channel.
- APs are too small and fast to be observed, PSPs 10-100ms
-
Pyramidal cells orientation makes them easily accessible from the scalp
- Tend to be synchronously active, big enough signal to measure
- Other cell types also have excitatory activity but EEG only sensitive to Pyramidal cells and post-synaptic potentials
- Activity from deep structures (thalamus, hippocampus) will not generally be observable
- A scalp electrode does not just record from the cortex below it.
- 6 channels – not enough to localise.
- 32 channels – can get more spatial info, but it’s more invasive for the patient.
- EEG also picks up signals from muscles which are electrical tissues – someone clenching jaw can distort the signal.
-
Poor spatial resolution - The electrical fields of the brain are propagative, so the electrode is sensitive to activity around not just directly underneath – poor spatial resolution
- However, has good temporal resolution
- That is why 2000+ electrodes would give better signal
OUTPUT
- The frequency content is like the speed of oscillation, the dominant frequency is characteristic of brain state
- Gamma – stimulated high energy >40Hz
- Beta – aroused, attentive 13-30Hz
- Alpha – relaxed 8-13Hz
- Theta – drowsy 4-8Hz
- Delta – sleep (N3) 0.5-4Hz
What is PSG what are the advantages and disadvantages
- Polysomnography is considered the gold standard of sleep assessment.
- based on laboratory monitoring that usually includes: electrical brain activity (EEG), muscle activation (EMG), eye movements (EOG),
- can also include breathing efforts and flow, oxygen saturation sensors (oximetry), video recording, and additional channels according to study requirements.
- Polysomnography provides detailed info: electrical tracings of brain activity, sleep architecture, sleep stages, sleep quality, arousals, breathing patterns, oxygen saturation, eye movements and leg movements during sleep.
- very rich and enables clinical research and diagnosis of a variety of sleep disorders including sleep apnoea, periodic movements in sleep, parasomnia (e.g., sleepwalking, night terrors), seizures, narcolepsy, REM sleep disorders, and insomnia.
- Another important use of polysomnography is for determination of daytime sleepiness (MSLT)
- ADVANTAGES:
- Most detailed set of data on the sleep process inc crucial info for brain and sleep medicine.
- Diagnosis of a variety of sleep disorders cannot be accomplished without specific info derived from PSG.
- objectively assess daytime sleepiness with procedures such as the multiple sleep latency test.
- Lab = provides full control and supervision on the tested individual under standardized conditions.
DISADVANTAGES
- Unique conditions that require tolerance = unnatural sleep environment (laboratory) and attached electrodes and sensors, which is a challenge to normal sleep patterns.
- It requires some adjustment in adults (first night effect), and it is certainly more challenging for infants and young children.
- sleep and brain itself is not working on 30 sec epochs therefore it is a simplification;
- costly procedure = only for one or two nights, which further compromises the representativeness of the data.
What is Sleep Staging?
What is the Alternative?
- Hori et al (1994) has - sleep stages in light sleep, before you get to N2. They have - -second epochs.
- There are - different types of wakefulness and - different types of N1.
- — widely used – TC – but may be seen in research if they want a more dynamic view of what is happening.
- Overcomes the original AASM limitation that in a 30-second epoch, there may be an overlap of 2 sleep stages.
Muller et al. stages are not homogenous, each stage contains > 1 type of activity. Important to remember that all stages are an oversimplification.
Sleep staging is the seperation of sleep into N1,N2, N3 and REM based on electrophysiological activity
N1 is light sleep characterised by a reduction in alpha waves, and increase in theta waves of 4-7HZ with slow eye movements - the presence of vertex sharp wave - a spike in EEG
N2 - presence of K complexes and short burst of sleep spindles. Muscluar activity occurs but EMG signals will decrease, and conscious awareness of external environment decrease
N3 – delta SWS, large amplitude slow waves of 0.5-2Hz. This is where parasomnias occur, so PSG may show muscle artefacts indicative of sleep walking, talking, night terrors etc. Time spent in N3 is proportional to prior sleep deprivation.
REM – rapid eye movements on EOG, low amplitude mixed frequency wake-like EEG, low chin EMG tone (muscle atonia). Increase in beta waves. Eye movements occur as eyes are controlled by brainstem.
- Studied in 30-second epochs, decide what is predominant. If there’s predominantly VSW but some sleep spindles towards the very end of the epoch, it’s defined as N1.
What are sleep spindles Where are they located When do they reach peak density
brief but powerful bursts of synchronous neuronal firing Thalamo-cortical networks Late at night
PSG provides detailed information of
- electrical tracings of brain activity,
- sleep architecture,
- sleep stages,
- sleep quality,
- arousals,
- breathing patterns,
- oxygen saturation,
- eye movements
- leg movements
