Global brain activity Flashcards
(27 cards)
What are alpha waves
- 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
Where do alpha waves normally originate from
- Predominantly originate from the occipital lobe during wakeful relaxation with closed eyes
When are alpha waves reduced
- Are reduced with open eyes, drowsiness and sleep
how is an EEG signal detected
- It takes many thousands of underlying neurons, activated together, in sync, to generate an EEG signal big enough to see
What are the basic requirements for EEG signal detection
- 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
What are the four basic EEG phenomena
- The alpha rhythm, 8-13Hz, awake subjects with eyes closed
- The beta rhythm, 14-60Hz, indicates mental activity and attention, eyes open
- Theta waves, 4-7Hz, indicates drowsiness and sleep or a pathological condition
- Delta waves, <4Hz, as in 3
Where do the theta rhythms come from?
- Come from the hippocampus
What is a K complex and what is it caused by
- K complex is an EEG waveform that occurs during stage 2 of NREM sleep
- Caused by calcium spikes
What allows thalamic cells to generate rhythmic, self-sustaining discharge patterns, even in the absence of external inputs
- 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
What causes the bursts of action potentials in a neuron during stage II sleep
- 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
What causes the oscillatory activity to change into a tonically active mode
- depolarisation of the cell(by injecting current or stimulating the cholinergic reticular activation system) transforms the oscillatory activity into a tonically active mode
What re the functions of brain rhythms
- 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
What are the three functional states of sleep
- Awake
- Non-REM
- REM
What is the type of modulation during the waking state
- 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)
Type of modulation during REM sleep
- Activation is also high
- Modulation is cholinergic
- Information source is internal
What are the functions of sleep and dreaming
- Conservation of metabolic energy
- Cognition
- Thermoregulation
- Neural maturation and mental health
What are two examples of structural imaging
- CT
- MRI
What are two examples of functional imaging
- PET
- fMRI
How do CT scans function
- 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
How does an MRI work
- 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)
What is the sequence of events for the acquisition of an MRI scan
- 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
What does a PET scan measure
- 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
What does an fMRI measure
- 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
What is the BOLD signal
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
