PSYC 444 MIDTERM 1

introduction material all the way to functions of sleep 2

what is sleep (give the three different viewpoints)

sleep can be viewed from three perspectives

• behavioural view - inactivity

• sleep scientist view - polysomnographic markers

• subjective experience - feeling of being asleep, insomnia

homeostasis vs dynamic balance

homeostasis is when an organism needs to maintain internal stability in face of environmental perturbations, dynamic balance is the system looks stable and unchanging, but is in fact constantly adapting to changes both in its internal states and in the environment 

Three main theories of sleep

1. Homeostatic theory: Sleep conserves energy in an energy-demanding organism and plays a key role in thermoregulation

2. Cognitive theory: Sleep maintains brain plasticity by downscaling synaptic strength, preserving cognitive function during wakefulness.

3. Clearance theory: Sleep allows the brain to clear metabolic byproducts accumulated during wakefulness (e.g., adenosine and ββ-amyloid).

what are considered the three classical states of consciousness?

wake, deep sleep and paradoxical sleep

what is the wake state classified as

mostly fast reflexes, an awareness of the environment, mental activity is spontaneous and intentional

what is the deep sleep stage classified as

• Slow wave sleep/delta sleep, non-rapid eye movement/NREM sleep 

• No explicit awareness of self or environment (exceptions) 

• High threshold of reactivity to external stimuli 

• Simple mental activity (images, thoughts), tendency towards amnesia 

what is the REM/paradoxical stage classified as

• Awareness of the dream environment/dream self, in some cases also awareness of sleeping self and physical environment (lucid dreams) 

• Relatively low threshold of awareness of external stimuli 

• Both spontaneous and intentional mental activity 

who recorded the first EEG and when?

1937: Loomis, Harvey & Hobart (Harvard) record and stage human

Wht observation led to the discovery of REM sleep?

cyclical and repeated eye movements were observed in young children during sleep, they hypothesized that the REM represented periods of dreaming ( by Aserinksy and Kleitman)

what are two ways to study sleep?

objective measures such as EEG, brain imagery, behavioural, experimental techniques

subjective estimation such as questionnaires and interviews - this could be retrospective or prospective

Retrospective sleep estimation (examples, pros, and cons)

Examples: Questionnaires (e.g., Pittsburgh Sleep Quality Index), interviews

• Pros: Easy to obtain

• Cons: Often unreliable, subject to bias, and do not correlate perfectly with objective measure

Prospective sleep estimation (examples, pros, and cons)

Definition: - Examples: Sleep diaries

• Pros: Can be modified to target specific sleep problems; eliminates some retrospective biases

• Cons: Labor-intensive, requires motivation, and captures only limited subjective information

what is actigraphy?

a watch like device that can measure gross levels of motor activity. this can be worn for many days to estimate sleep - wake patterns. it will estimate sleep latency, sleep length, restless legs

pros and cons of actigraphy

pros: non - invasive, can be used at home, can collect data over multiple days

cons: only records activity - rest patterns limited data

brain imagining cons for sleep

brain imaging can be used such as MRI, fMRI, SPECT, PET but low temp resolution and it is kind of uncomfortable because subjects cannot move its invasive and expensive

Functional near-infrared spectroscopy 

non-invasive, portable , similar to fMRI &EEG 

• Measures hemoglobin concentration, absorption of near infrared light 

depth electrodes

used in pre-operative cases or for epilepsy (when it isn’t responsive to meds)

• type of intracranial EEG inside the head

• its implanted inside for many days and can record sleep patterns

• good spatial and temporal resolution

single cell recordings, local cortical field potentials

• invasive yet precise (good temporal and spatial resolution)

• records from a single individual cell

• records from extracellular space (summed activity from nearby electrodes) measures level of synchrony

Polysomnography 

• used to diagnose sleep disorders

• objective method of sleep scoring

• EEG, EOG, EMG, EKG

• can add more sensors that are relevant to your research on top of that

high density EEG

this has more electrodes with high spatial resolution along with temporal brain dynamics

EOG (Electrooculogram)

(cue - O looks like an eyeball)

measures eye movements both horizontally and vertically and is used to categorize REM sleep, and slow rolling eye movement during SWS

EMG (Electromyogram)

(cue - M for muscles)

measures muscle tone, typical to measure chin, legs and is used to detect muscle atonia characteristics of REM sleep, for body mvoement, and also for diagnostic of some sleep disorders (teeth grinding, restless leg)

EKG (or ECG) Electrocardiogram

used to measure heart variability and for diagnosis of cardiac anomalies in sleep

EEG - Electroencephalogram

• used for the detection of sleep onset and sleep stage identification

• provides global summation of all activity, there is usually one dominant frequency (which determines what stage you are in)

• consists of aggregated activity of thousands of pyramidal neurons perpendicular to the skull

the meaning of amplitude in EEG

• the amplitude signifies the level of synchrony of the neuronal activity

• low amplitude for asynchronous ( when neurons discharge at dif times)

• high amplitude for synchronous ( when neurons discharge at the same times)

EEG frequencies bands

• Beta - busy brain (13-30Hz) - Wake

• Alpha - awake but relaxed (8-13Hz) - Resting wake, eyes closed

• Theta -transition (4 -8 Hz) - sleep onset, NREM sleep stage 1,2, REM 

• Delta - deep sleep (0.5 - 4Hz) - slow wave sleep, NREM 3

• Hz = frequency of brain waves, higher frequency = more active

what is the longest sleep stage, lasting 45-55 percent % of sleep?

N2 - NREM sleep stage 2

Hypnogram (a line graph that shows the different stages of sleep) features

• REM periods get longer by the end of the night, while SWS disappears

• Hypnogram represents in visual terms progression of sleep stages during the period of sleep stages, notes sleep architecture

why is it difficult to pinpoint the exact moment of sleep onset?

because sleep onset is a gradual process, sleepiness is felt well before sleep onset

what aspects are sleep onset characterized by?

General slowing of brain activity - cortico-thalamic neuron recording:

gradual slowing down of the firing rate 

• Eye movements – rolling 

• Diminished responsiveness to outside stimuli and of cognitive processes 

• Hypnagogic imagery 

NREM 2 characterization

• theta activity here

• presence of K complexes and sleep spindles!

• 50 percent of adult sleep is this sleep

• ranges from simple to complex sleep

k complex

• A bipolar wave (much like a slow wave), lasts at least .5 sec (0-2 Hz)

• involved in preserving different sleeps by playing a role in the thalamo – cortical gating (brain's filtering process where the thalamus controls which sensory and cognitive signals reach the cerebral cortex) 

• could be important for memory consolidation

• marks begining of NREM2 sleep

• can be spontanoeus or evoked

sleep spindle

• sigma activity(12 – 14 Hz) 

• associated with memory consolidation 

• Associated with protective processes against neurodengeration and with brain plasticity 

• marks NREM 2 beginning

NREM 3 – Slow Wave Sleep 

• delta activity (0 – 4Hz) 

• brain activity is slow and synchronized (higher in amplitude) 

• where most parasomnias happen:sleep walking

• predominant in the first half of sleep

REM sleep

• stands for rapid eye movement sleep, aka parodoxical sleep

• mixed frequencies

• muscle atonia (paralysis) - babies don’t possess this yet

• characterized by rapid saccadic eye movements

• breathing and cardiac activity are irregular

• dreams and nightmares often happen here

• tonic and phasic

clinical significance of sleep spindles

• Altered spindle activity in some disorders such as schizophrenia 

• Can be used as indirect indicator of more global deficits in thalamocortical functioning 

• Change with age 

slow wave sleep (SWS)

• slow, synchronous EEG oscilations

• potentially locally generated

• potential functions: memory consolidation, synaptic homeostasis, glymphatic function, restorative function, reactivity 

• SWS is important for LTP

rapid eye movement

• Function is still largely unknown 

• REMs; possible saccadic movements to observe the dream environment (the “scanning hypothesis”) 

• A possible index of intensity of dream experience 

• Could be a marker for depression 

• Plays potential role in learning