Global Brain Activity

Question 1

what rhythms are there in the brain?

Answer 1

sleeping and waking
breathing cycles
steps of walking
stages of night sleep

Question 2

what does an electroencephalogram (EEG) measure?

Answer 2

generation of small fields in pyramidal cells

takes many thousands of underlying neurons to generate an EEG big enough to see

Question 3

what are the basic requirements for signal detection?

Answer 3

a whole population of neurons must be active in synchrony to generate a large enough electrical field at the level of the scalp
neuron population must be aligned in parallel orientation
(so they summate, not cancel each other out)

Question 4

what is does synchronous activity depend on?

Answer 4

number of active cells, total amount of excitation, timing of activity
in pyramidal cell layer, each neuron receives thousands of synaptic inputs
if inputs are irregular or out of phase, sum has small amplitude
if inputs are activated at the same time, EEG waves will tend to be in phase and amplitude larger

Question 5

how are synchronous rhythms generated?

Answer 5

brainstem nuclei modulate the rhythm of interactions from collective behaviour of neurons

Question 6

what is a one neuron oscillator?

Answer 6

thalamic cells have set of voltage-gated ion channels which allow each cell to generate rhythmic, self-sustaining discharge patterns, even in the absence of external inputs
the rhythmic activity of each thalamic pacemaker cell becomes synchronised with many other thalamic cells

Question 7

what does the oscillatory mode of thalamocortical neurons correspond to?

Answer 7

sleep state
tonically active mode corresponds to awake state
bursts of APs are evoked when neuron is hyperpolarised to activate low threshold Ca2+ channels
bursts account for spindle activity of EEG recording (stage II sleep)
depolarisation of cell transforms oscillatory activity into tonically active mode (by injecting current or stimulating cholinergic reticular activation system

Question 8

functions of brain rhythms

Answer 8

sensory input: thalamus-cortex
activity coordination (binding) or different cortical regions (synchrony, oscillations)
meaningless by-product of feedback circuits
EEG rhythms: window of functional states of the brain

Question 9

behavioural criteria for sleep

Answer 9

reduced motor activity
decreased response to stimulation
stereotypic postures
relatively easy reversability

Question 10

what are the functional states of sleep?

Answer 10

awake
non-REM
REM

Question 11

which neurons control sleeping and waking?

Answer 11

part of diffuse modulatory neurotransmitter systems

control rhythmic activity of the thalamus and EEG rhythms of the cortex

Question 12

diffuse modualtory systems in waking state

Answer 12

activation is high
modulation is aminergic (norarenaline, serotonin)
information source is external

Question 13

diffuse modulatory systems in REM sleep

Answer 13

activation is high
modulation is cholinergic
information source is internal

Question 14

histamine-containing neurons

Answer 14

help in control sleep and waking

found in tuberomammillary nucleus in the hypothalamus

Question 15

what function does sleep/dreaming have?

Answer 15

conversion of metabolic energy
cognition
thermoregulation 
neural maturation 
mental health

Question 16

imaging techniques

Answer 16

structural or functional

Question 17

what is structural imaging used for?

Answer 17

measures the spatial configuration of types of tissue in the brain static maps)
CT, MRI

Question 18

what if functional imaging used for?

Answer 18

measures movement-to-movement variable characteristics of the brain that may be associated with changes in cognitive processing (dynamic maps)
PET, fMRI

Question 19

what are CT scans?

Answer 19

computerised tomography
based on amount of x-ray absorption in different types of tissue
bone absorbs most, CSF absorbs least, brain matter is intermediate
used in clinical settings - to diagnose tumours, haemorrhaging, other gross abnormalities

Question 20

what are MRI scans?

Answer 20

magnetic resonance imaging
completely safe, people can be scanned many times
better spatial resolution than CT
better discrimination between white and grey matter
can be adapted for detecting changes in blood oxygenation associated with neural activity (fMRI)

Question 21

sequence of events in an MRI scan

Answer 21

magnetic fields of protons = initially random
add external magnetic field and some protons align
brief radio wave pulse orients protons to 90 degrees, producing measurable MR
protons return back and new brains slice is scanned

Question 22

physiology underpinning functional imaging

Answer 22

brain makes up 2% body weight but 20% oxygen uptake
oxygen and energy needs are constantly supplied by local blood supply
when neuron metabolic activity increases, so does blood supply to that area

Question 23

what is the difference between PET and fMRI?

Answer 23

PET measures change in blood flow to a region
fMRI is sensitive to O2 concentration in the blood
experimental condition always compared to baseline
indirect measures of neuronal activity

Question 24

what is a PET scan?

Answer 24

positron emission tomography
based on blood volume
involves radioactivity (radioactive tracer in blood)
participants scanned once or a few times
effective spatial resolution
sensitive to whole brain
can use pharmacological tracers

Question 25

what is a (BOLD) fMRI scan?

Answer 25

functional magnetic resonance imaging 
based on blood oxygen concentration 
no radioactivity 
participants scanned many times 
some brain regions are hard to image - e.g. near sinuses

Question 26

what is a BOLD signal?

Answer 26

blood oxygen level dependent contrast
measured in fMRI
relates to concentration of oxy and deoxyhaemoglobin

Question 27

what does HRF mean?

Answer 27

haemodynamic response function

describes changes of BOLD signal over time