Brain rhythms and sleep Flashcards
What are rhythmic activities (oscillations) of the brain?
- Rthyms that differ in their frequency, origin and reactivity to changes in sensory input and task demands:
- All rhtyms are characterised by the periodic re-occurance of similar patterns at a relatively constant rate
- Some oscillations have been shown to be linked to a specific behaviour but the function of many osciillations are still unclear
- e.g.
- Circadian rhthym - regulates our sleeping anf waking patterns. Aligns with light-dark (day-night) cycles and is driven by an intrinsic circadian clock
- Hibernation (longer rhtymic period)
- Breathing (shorter rhythmic period)
- Cerebral cortex : Range of electrical rhythyms depending on state of consciousness (recorded using EEG)
How can we record oscillations in the cerebral cortex?
- The electroenecephaloram (EEG)
- Measurement of generalised cortical activity
- Non-invasive, painless
- Diagnose neurological conditions such as epilepsy, sleep, disorders, research
**W
What is an EEG recording?
- Very small electrical fields generated by synaptic currents in pyramidial cells
- The signal is only seen by the scalp EEG electrode if thousands of them contribute their small volatage at the same time (synchronous firing)
What drives oscillations?
- Mechanisms of synchronous rhythms that can be led by a pacemaker or that arise from collective behaviour of all participants
How does the thalamus act in oscillation?
- The thalamus can act as a powerful pacemaker
- Can generate very rhythmic, self sustaining, discharge patterns even when there in no external input
- Thalamocorttical axons
- Thalamus - cortex = excited cortical neurons
- Cortical cells will oscillate to the same rhythm as the thalamus
What are circadian rhythms?
Circadian Rhythms
- circa = approximately; dies = a day
Daily cycles of light and dark
— Schedules of circadian rhythms vary among species
— Physiological and biochemical processes in body: Rise
and fall with daily rhythms
— Daylight and darkness cycles removed, circadian rhythms
continue
— Brain clocks
What role does the circadian rhythm play in physiological function?
- Sleep and wakefulness
- Temperature
- Growth hormone
- Cortisol
- Potassium
What is the suprachiasmatic nucleus of the circadian rhythm?
- A brain clock
- Intact SCN produces rhythmic message : SCN cell firing rate varies with the circadian rhythm
- Each SCN cell is a small clock
- Light sensitive input pathway
- Clock (SCN)
- Output pathway
- Allows the clock to control certain brain and body functions according to the timing of the clock
- Circadian rhythmicity of behaviour, hormone levels, sleeping and waking, metabolism, feeding, drinking
What is sleep?
- A readily revereseible state of reduced responsiveness to , and interaction with, the environment
- SCN = important for maintaining circadian rhythmicity of sleep-wake cycles. Sleep is also regulated by mechanisms other than the circadian clock, primarily the amount and timing of prior sleep
What are the stages of sleep?
Stage 1: Transitional sleep. Alpha rhythms of relaxed waking becomes less regular and
wane and eyes start to make slow, rolling movement. It is fleeting and only last a few
minutes.
Stage 2: Slightly deeper, may last 5-15 mins. Includes occasional 8-14Hz sleep spindle
generated by a thalamic pacemaker). And high-amplitude K-complex. Eye movements
almost cease.
Stage 3: Large amplitude, slow delta rhythms. Eye and body movements usually absent.
Stage 4: Deepest stage of sleep: Large EEG rhythms of 2Hz or less. Can last 20-40 mins.
REM: Sleep will lighten from stage 4 to stage 2 (for about 15 mins) before entering brief
period of REM. Frequent eye movements, fast EEG rhythms.
As night progresses, there is general reduction in NREM and sleep and an increase in REM
Half nights REM sleep occurs during its last third
Obligatory ‘NREM’ cycle before next REM period begins
*Consider the implications for teenagers and night owls. Will very rarely receive all the REM
sleep they require as being woken up too early.
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What are the physiological changes during non-REM and REM sleep?
- Non-REM sleep
- Steady HR, BP and respiration rate
- Muscles relaxed
-REM sleep - Fluctuating HR, BP and respiration rate
- Skeletal muscles profoundly relaxed (body movements may occur)
What are the proven benefits of a full night of sleep?
Proven benefits of a full night of sleep…
* Makes you live longer
* Enhances your memory
* Makes you more creative
* Keeps BMI low and decreases food cravings
* Protects from dementia and cancer
* Wards of the flu
* Lowers risk of heart attack, stroke and diabetes
* Reduces depression and anxiety
How does sleep aid memory before and after learrning?
Sleep aids memory before learning:
* The hippocampus offers a short term reservoir/temporary information store, for new
memories. BUT it has a limited storage capacity (e.g. a USB memory stick). Exceed its
capacity and you may not be able to add more information or, equally as bad, you
may overwrite one memory with another (called interference forgetting).
* How does the brain deal with this capacity issue?
Sleep: Acts as a file-transfer mechanism. It moves recently required information to
more permanent, long-term storage locations, freeing up short term memory stores.
* Result? We awake with a refreshed short-term storage and greater ability for new
learning.
Which sleep period offers a greater memory saving benefit?
- For facts based, text- book like memory : Early night sleep, rich in deep NREM
- NREM - can also helpo you recover memories you could not retrieve before sleep
- Important for forgetting info we no longer need- actively deletes memories during NREM to improve learning efficiency and improve the ease of memory recollection
