sleep cycle, circadian rhythm and memory Flashcards
how is sleep defined and how is it studied?
reduced motor activity, reduced response to stimulation, stereotypic postures like eyes closed, and easy reversibility
studied by looking at muscle movements with electromyography, eye movements with electro-oculography and brain activity
with electroencephalography
EEG - what does it do/require/it’s benefits/drawbacks?
measures the synchronous electrical activity from large populations of neurons in the brain using electrodes on the scalp
a large number of neurons is required for any electrical activity to be detected
its non-invasive, has high temporal resolution but low spatial resolution and data is easily gathered
you can add different kinds of brain waves??
define non-REM sleep and it’s stages
Decreased neuronal activity, lower brain temperature and metabolic rate
Stage 1 - drowsiness - awaken easily, lower eye and muscle activity, low voltage activity of mixed frequencies, mostly theta waves
Stage 2 - light sleep - body temp drops, heart rate slows down, EEG shows ‘K complexes’ (big spike) and ‘sleep spindles’ (bursts of high frequency activity)
Stage 3 - deep sleep - slow delta waves interspersed with faster waves. Sleep walking, dreaming, talking etc…
Stage 4 - very deep sleep - similar to stage 3, delta waves exclusively on EEG
what do the main brain waves look like?
alpha is like a smooth/curved tree line
theta is like a larger, more spaced line of peaks, like hills
delta are biggest, look like mountain range
beta are smallest, look like a spikey tree line
describe REM sleep
EEG mimics wakefulness
Closed eyes move rapidly from side to side
Perhaps intense dreams
why is REM sleep described as paradoxical?
Termed paradoxical sleep - all muscles relax (except eye muscles) yet brain activity mimics wakefulness, brain temperature and metabolic rate rises like when awake, yet all skeletal muscles are atonic (can’t move)
Eyes, middle ear ossicles and diaphragm maintain active (and smooth muscle ofc)
describe human sleeping patterns in terms of the stages and specifically young adults
It’s not linear, you don’t have to go stage 1,2,3,4, REM, you can move between them
In young adults - 5% in stage 1,
50-60% in stage 2,
3 and 4 are 15-20%, REM is 25 %
how is sleep regulated?
by norepinephrine and serotonin neurons in the brain stem
inhibition of motor neurons
‘diffuse modulatory system’ (a small amount - a few thousand - neurons) controls rhythmic behaviour in the thalamus
wakefulness - how is it achieved from sleep, what can cause sleep/coma?
activation of neurons in brain stem - depolarising effect - causes wakefulness
lesions of the brain stem can cause sleep or coma
in the non-rem stage, what happens in the brain?
decreased firing in the brain stem and spindles and delta waves indicate thalamus activity
in the REM stage what happens in the brain?
no activity in frontal lobe, the raphe nuclei and the locus coeruleus
inhibition of the motor neurons
what are some theories on dreaming?
it’s circuit testing
exercising synapse when there’s no external activity
memory consolidation
circadian rhythms - how do they work?
they are endogenous - so they persist without external cues, however, external cues can cause a shift in the schedule, but you would still be sleeping/awake for same amount of time
what areas of the brain modulate circadian rhythms?
Regulated by suprachiasmatic nucleus in the hypothalamus, connected to the eyes by the retinohypothalamic tract
So light is directly linked to circadian rhythms
define -
1) learning
2) memory
3) recall
4) the engram
learning = acquisition of information
memory = storage of learned information
recall = reacquisition of stored information
the engram = physical embodiment of a memory
types of memory - there are four, what are they?
procedural = skills not available to the conscious mind
declarative = available to conscious mind and can be explained in symbols/language
explicit = memory that can be consciously recalled, like an event
implicit = not consciously recalled, learning a skill, conditioning
some things can have an overlap
what are the three durations of memory?
immediate = seconds
short term/working = minutes
long term = days, months, years
the temporal lobe - what can electrical stimulation cause?
what is the relevance of epileptic seizures and temporal lobectomy?
stimulation = hallucinations and recollection of the past
seizures = complex sensations and memories experienced suggest a link to temporal lobe
a temporal lobectomy resulted in fewer seizures in an epileptic memory but the inability to make more long term memories
what structures in the brain, aside from the temporal lobe, are involved in memory?
prefrontal cortex = working memory
hippocampus = converts long term to short term, particularly declarative
amygdala - processes sensory input so involved in emotional implicit memory like fear/smell
cerebellum = involved in procedural memory like balance and sensory motor processing
hippocampus - structure/input/differences?
three layers + dentate gyrus
input = entorhinal cortex
enlarged in people whose work requires spatial memory
what is the most popular mechanism of memory?
Hebbian synapse concept = two neurons spiking at the same time form a stronger connection
synapses have plasticity - how so? long term/short term?
facilitation - when a synapse experiences an increased effect on the postsynaptic neuron from the same stimulus, due to more sensitive Ca2+ channels
depression = same stimulus produces weaker postsynaptic response due to vesicle depletion
these changes can be short term, or long term but long term requires postsynaptic changes
both facilitation and depression can be involved in making memories, even if you would expect depression to weaken memory (not necessarily the case)
what is long term potentation?
its lasting facilitation
1st discovered in hippocampus between CA3 and CA1
a presynaptic neuron gets better at causing a greater response in postsynaptic neurons increase EPSP from same stimulus
what is long term depression?
a decrease in amplitude of EPSP for the same stimulus
how was memory demonstrated in that snail thing?
using a less complicated brain can be useful
showed an increase in effect from same stimulus
also demonstrated habituation as it stopped hiding it’s sensitive gills when it realised the stimulus posed no threat
what cellular mechanisms are involved in long term potentiation/depression?
changes in length require receptor activation - glutamate or serotonin
second messengers like Ca2+ and cAMP can be used
the process often requires protein phosphorylation and then protein synthesis, if a structural change is desired
specifically how does long term potentiation occur?
release of Ca2+ from presynaptic neuron, ions move into post via AMPA, from there Ca2+ triggers kinases to do some phosphorylating to increase AMPA activity and make the postsynaptic neuron more sensitive
