Global brain activity

Question 1

What are alpha waves

Answer 1

• Alpha waves are neural oscillations in the frequency range of 7.5-12.5 Hz
• They arise from synchronous and coherent(in phase or constructive) electrical activity of thalamic pacemaker cells
• AKA berger’s wave

Question 2

Where do alpha waves normally originate from

Answer 2

• Predominantly originate from the occipital lobe during wakeful relaxation with closed eyes

Question 3

When are alpha waves reduced

Answer 3

• Are reduced with open eyes, drowsiness and sleep

Question 4

how is an EEG signal detected

Answer 4

• It takes many thousands of underlying neurons, activated together, in sync, to generate an EEG signal big enough to see

Question 5

What are the basic requirements for EEG signal detection

Answer 5

• A whole population of neurons must be active in synchrony to generate a large enough electrical field at the level of the scalp
• This population of neurons must be aligned in a parallel orientation so that they summate rather than cancel out

Question 6

What are the four basic EEG phenomena

Answer 6

1. The alpha rhythm, 8-13Hz, awake subjects with eyes closed
2. The beta rhythm, 14-60Hz, indicates mental activity and attention, eyes open
3. Theta waves, 4-7Hz, indicates drowsiness and sleep or a pathological condition
4. Delta waves, <4Hz, as in 3

Question 7

Where do the theta rhythms come from?

Answer 7

• Come from the hippocampus

Question 8

What is a K complex and what is it caused by

Answer 8

• K complex is an EEG waveform that occurs during stage 2 of NREM sleep
• Caused by calcium spikes

Question 9

What allows thalamic cells to generate rhythmic, self-sustaining discharge patterns, even in the absence of external inputs

Answer 9

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

Question 10

What causes the bursts of action potentials in a neuron during stage II sleep

Answer 10

• Bursts of action potentials are evoked when the neuron is hyperpolarised enough to activate low threshold Ca2+ channels
• These bursts account for the spindle activity of the EEG recording

Question 11

What causes the oscillatory activity to change into a tonically active mode

Answer 11

• depolarisation of the cell(by injecting current or stimulating the cholinergic reticular activation system) transforms the oscillatory activity into a tonically active mode

Question 12

What re the functions of brain rhythms

Answer 12

• Sensory input –> thalamus –> cortex
• Activity coordination(binding) of different cortical regions(synchrony oscillations)
• Meaningless by product of feedback circuits and connections
• EEG rhythms - window of the functional states of the brain

Question 13

What are the three functional states of sleep

Answer 13

• Awake
• Non-REM
• REM

Question 14

What is the type of modulation during the waking state

Answer 14

• Activation is high
• Modulation aminergic(NE locus coeruleus), 5-HT(raphe nuclei), and the information source is external
• Histamine-containing neurons in the tuberomammilary nucleus(tmn) of the hypothalamus are also involved(drowsiness is a side effect of an antihistamines which suppress the TMN network)

Question 15

Type of modulation during REM sleep

Answer 15

• Activation is also high
• Modulation is cholinergic
• Information source is internal

Question 16

What are the functions of sleep and dreaming

Answer 16

• Conservation of metabolic energy
• Cognition
• Thermoregulation
• Neural maturation and mental health

Question 17

What are two examples of structural imaging

Answer 17

• CT

- MRI

Question 18

What are two examples of functional imaging

Answer 18

• PET

- fMRI

Question 19

How do CT scans function

Answer 19

• Based on the amount of x-ray absorption in different types of tissue
• Bone absorbs the most(the skull appears white), CSF absorbs the least(the ventricles appear black) and the brain matter is intermediate(grey)
• Used in clinical settings eg to diagnose tumours or identify haemorrhaging or other gross brain anomalies

Question 20

How does an MRI work

Answer 20

• Completely safe, so people can be scanned many times
• Provides a much better spatial resolution
• Provides better discrimination between white and grey matter
• Can be adapted for detecting the changes in blood oxygenation associated with neural activity(fMRI)

Question 21

What is the sequence of events for the acquisition of an MRI scan

Answer 21

• Magnetic fields of protons initially random
• Add external magnetic field and some protons align
• Brief radio wave pulse orients them 90 degrees and produces a measurable MRI signal
• The protons return back(relax) and a new brain slice is scanned

Question 22

What does a PET scan measure

Answer 22

• Measures change of blood flow to a region
• Based on blood volume
• Sensitive to the whole brain
• Involves radioactivity(signal depends on radioactive tracer)
• Participants scanned once or few times

Question 23

What does an fMRI measure

Answer 23

• Is sensitive to the concentration of oxygen in the blood
• No radioactivity(signal depends on deoxyhaemoglobin levels)
• Participants scanned many times
• Some brain regions(eg near sinuses) are hard to image

Question 24

What is the BOLD signal

Answer 24

BOLD signal - blood oxygen level dependent contrast, is the signal measured in fMRI that relates to the concentration of oxy- and deoxyhaemoglobin in the blood

Question 25

What is HRF

Answer 25

• Haemodynamic response function, describes the changes of the BOLD signal over time

Question 26

What does structural and functional imaging reveal

Answer 26

• Structural imaging reveals the static physical characteristics of the brain(useful in diagnosing disease), whereas functional imaging reveals dynamic changes in brain physiology(might correlate with cognitive function)

Question 27

How does neural activity affect PET and fMRI scans

Answer 27

• Neural activity consumes oxygen from the blood which triggers an increase in blood flow to that region(PET)
• and a change in the amount of deoxyhaemoglobin in that region(fMRI)