Global brain activity Flashcards
THE EEG
i) where on the cortex does the EEG record signals from?
ii) how good is the spatial resolution? how easily can you tell signals apart that are close together?
iii) how good is temporal resolution
iv) name two situations it can be used for clinically
v) name three advantages
i) the surface
ii) poor spatial resolution - cant tell signals apart that are close together
iii) good temporal resolution - can record signals that happen close together in time
iv) to look at physiology of sleep and in epilepsy
v) non invasive, can be used in children and no negative effects
THE EEG - GENERATING A SIGNAL
i) which cell type generate small fields of electrical activity which can be detected by the EEG?
ii) what type of activity is needed to be detected by the EEG?
iii) name the two basic requirements for signal detection (how many neurons activated and what alignment)
iv) what does the amplitude of the EEG signal partly depend on?
i) pyramidal cells
ii) synchronous activity - need lots of neurons activating at the same time to record the signal
iii) 1) whole population of neurons must be active in synchrony to generate a large enough elec field at the top of scalp 2) the pop of neurons must be aligned in parallel orientation so they summate rather than cancel each other out
iv) amplitude of signal can depend on how synchronous the activity of the underlying neuron is
EEG AND BEHAVIOUR STATES
i) what amplitude of signals are seen in an epileptic fit? are the same or different timings of waves seen at each electrode?
ii) what rhythm is seen when awake but eyes closed
iii) what rhythm is seen when awake and eyes open?
iv) what rhythms are also seen in REM sleep (when dreaming)
v) which two brain areas give critical inputs in non REM sleep? give two characteristics of the EEG signal at this time
vi) which type of brain rhythms are the slowest?
i) high amplitude and same timing at each electrode
ii) awake eyes closed = alpha rhythm
iii) awake eyes open = beta rhythm
iv) REM sleep also see beta rhythm
v) thalamus and brainstem give inputs in non rem sleep very synchronous and high amplitude signals during this time
vi) delta
GENERATION OF SYNCHRONOUS RHYTHMS
i) which cell gives rhythm to all cells?
ii) where are neurons taking in feedback from?
iii) which brain area can give specific rhythm input into the cortex?
iv) what does large networks of cells in the cortex firing at the same frequency cause? (2)
i) pacemaker neuron
ii) eachother
iii) thalamus
iv) firing at the same freq > oscillations and synch activity
RHYTHM FREQUENCIES
What is the frequency of
i) alpha ii) beta iii) theta iv) delta rhythms?
I) alpha = 8-13Hz
ii) beta = 14-16Hz
iii) theta = 4-7Hz
iv) delta = 4Hz
THALAMIC CELLS
i) what type of channels in the cells allows generation of rhythmic and self sustaining discharge patterns? are external inputs needed for these signals to be sustained?
ii) what does the rhythmic activity of each thalamic pacemaker neuron then become synchronised with? when does this happen?
iii) what type of activity occurs in the cortex in slow wave sleep? what does this correlate with in the thalamus?
iv) what mechanism allows bursts of activity in the thalamus?
v) what type of activity is seen in waking? do thalamic cells fire more or less often than in slow wave sleep? how is amplitude different?
i) voltage gated channels - allows these signals to be sustained even without external input
ii) activity of each thalamic pacemaker becomes synch with many other thalamic cells - happens during sleep
iii) large synchronous activity in slow wave sleep which correlates with bursts of activity from thalamic cells
iv) opening of voltage gated channels in thalamic cells generate large calcium spikes therefore Na channels open and cause bursts of activity
v) waking = no bursts of activity and no co-ordination of lots of cells firing together - thalamic cells fire less frequently and have lower amplitude
SLEEP
i) which four behavioural criteria can sleep be defined by?
ii) what are the three functional states of sleep?
iii) what amplitude/frequency of waves are seen when awake? which two rhythms are seen
iv) what brain area is the master controller of sleep wake states? what does it control and what does this cause?
v) which stage of sleep are theta rhythms seen?
vi) which stage of sleep are spindles and K complexes seen? is this REM or non REM
i) reduced motor activity, decreased response to stimulation, stereotypic postures, relatively easy reversibility
ii) awake, REM, non REM
iii) awake = high frequency, low amplitude - alpha and beta rhythms
iv) brainstem > controls firing of the thalamus which controls the cortex
v) theta = stage 1 non rem sleep
vi) spindles/K complex - stage 2 non REM sleep
FUNCTION OF SLEEP AND DREAMING
i) give four potential reasons
ii) which rhythms are seen in REM sleep?
iii) what type of NT activity is there in waking and in REM sleep
i) conservation of metabolic energy, cognition (consolidate info), thermoregulation, neural maturation and mental health
ii) beta rhythms
iii) waking = aminergic eg noradrenaline
REM sleep = cholinergic
IMAGING TECHNIQUES
i) what does structural imaging measure? give two examples
ii) what does functional imaging measure? give two examples
i) measures spatial config of types of tissue in brain (static) = CT and MRI
ii) measures changing characteristics of the brain that may be associated with changes in cognitive processing = PET and fMRI
STRUCTURAL IMAGING
i) what colour do bones and fluid appear on CT?
ii) which tissue absorbs the most and least X-ray in CT?
iii) which technique doesn’t use ionising radiation?
iv) does CT or MRI have better spatial resolution?
i) bone = bright white and fluid = black
ii) most abs is bone and least abs is fluid eg CSF
iii) MRI doesn’t use ionising rad therefore sager
iv) MRI has better spatial resolution
what is the sequence of events to generate an MRI picture?
(4 steps)
1) magnetic field of protons are initially random
2) add an external magnetic field and some protons align
3) then add a brief radio wave pulse which orientates the protons at 90 degrees to produce a measurable MR signal
4) protons return back to normal when a new brain slice is scanned
FUNCTIONAL IMAGING
i) which type of scan measures change of blood flow to a region?
ii) which type of scan measures concentration of oxygen in the blood?
iii) which scan involves injection of radioactive dye?
iv) what does an fMRI signal depend on? what is this signal called? what describes the change of this signal over time?
v) does PET or fMRI have better spatial resolution? vi) what is a requirement for functional imaging?
i) change of blood flow = PET
ii) oxygen conc = fMRI
iii) PET = radioactive dye
iv) fMRI signal depends on levels of deoxyhaemoglobin - BOLD signal - changes in this signal over time measured by HRF (haemodynamic response function)
v) PET has better spatial resolution vi) must have a baseline to compare it to as it measures relative changes
PET/fMRI SCANNING
i) what are 5 key parameters for PET?
ii) how can pharmalogical tracers be utilised in PET scanning?
iii) what is the BOLD signal? which imaging modality is the signal used for?
iv) how good is temporal and spatial resolution for fMRI?
v) give an example of an area that may be hard to image using fMRI
1) based on blood volume/flow 2) uses radioactivity 3) poor temporal resolution 4) good spatial resolution 5) can use pharmacological tracers
ii) inject the tracer and record where the receptors are for it
iii) fMRI - relates to conc of oxygen and deoxy Hb in blood
iv) good temporal but poor spatial resolution
v) some brain regions eg near sinuses
