Global brain activity Flashcards
What is meant by rhythmic environment?
Temperature, day and night, tides
What do brain rhythms control?
sleeping and waking, breathing cycles, steps of walking, stages of night sleep
What is an electroencephalogram used for?
Physiology of sleepy
Epilepsy
Correlates with pathology and behavioural states
How is an EEG produced?
Generation of small fields in pyramidal cells
What are 2 basic requirements for 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 they summate rather than cancel out
What does the amplitude of the EEG depend on?
How synchronous the activity of the underlying neuron is
Number of active cells
Total amount of excitation
Timing of activity
What is the alpha rhythm?
Person is awake with eyes closed
What is the beta rhythm?
Person is awake with eyes open - indicates mental activity and attention
What are theta waves?
Indicates drowsiness and sleeping or pathological condition
Which rhythm is present in REM sleep?
Beta rhythm
Which waves are found in stage 3 non REM sleep?
Delta waves
How is the synchronous rhythm generated?
Analogous to pacemaker
Improvisation and timing arises from the collective behaviour of the neurons together
The rhythmic activity of each thalamic pacemaker neuron then becomes synchronised with many other thalamic cells via a hand-clapping kind of collective interaction.
What modulates the synchronous rhythm?
Brainstem nuclei modulate interactions between the thalamus and the cortex
What do thalamic cells have to aid the rhythmic activity?
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.
What are the functions of brain rhythms?
Functions are unknown however
Sensory input – thalamus – cortex
Activity coordination (binding) of different cortical regions (synchrony, oscillations)
Meaningless by-product of feedback circuits and connections
List the behavioural criteria for sleep
Reduced motor activity
Decreased response to stimulation
Stereotypic postures
Relatively easy reversibility
What are the 3 functional stages of sleep?
Awake
Non-REM - has 4 stages (1,2,3,4,3,2)
REM
What are the functions of sleep and dreaming?
Unknown however
Conservation of metabolic energy
Cognition
Thermoregulation
Neural maturation and mental health
Name the imaging techniques of the brain
Structural imaging - Measures of spatial configuration of types of tissue in the brain - CT and MRI
Functional imaging - Measures the moment-to-moment variable characteristics of the brain that may be associated with changes in cognitive processing (dynamic maps) - PET and fMRI
How does the image appear like on a CT scan?
Bone absorbs the most (the skull appears white), cerebrospinal fluid absorbs the least (the ventricles appear black) and the brain matter is intermediate (grey).
How are CT scans formed?
Based on the amount of X-ray absorption in different types of tissue.
Where are CT scans used?
Used in clinical settings, e.g. to diagnose tumours or identify haemorrhaging or other gross brain anomalies.
What are the advantages of MRI?
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).
Describe the sequence of events in acquisition of an MRI scan
Magnetic fields of protons initially random
Add external magnetic field and some protons align
Brief radio waves pulse orients them to 90 degrees and produces a measurable MR signal. The protons return back and a new brain slice is scanned
What underpins functional imaging?
Basic physiology
The brain makes up 2% of the body weight, but consumes 20% of the body’s oxygen uptake; it can’t store oxygen and only stores little glucose.
Oxygen and energy needs are constantly met by the local blood supply. When the metabolic activity of neurons increases, then the blood supply to that region increases as well.
What does PET measure?
Changes to blood flow to a region
What is fMRI sensitive to?
Concentration of oxygen in the blood
Why do we compare an experimental condition with a baseline condition?
Constant activity
Is functional imaging a direct or indirect way of measuring brain activity?
Indirect
What is PET based on?
Blood volume
What does PET use?
Radioactive ligands
Pharmacological tracers
What is fMRI based on?
Blood oxygen concentration (BOLD)
No tracers - concentration of deoxyhemoglobin
What is the temporal resolution of PET scans?
30’’
What is the temporal resolution of fMRI scans?
1-4’’
What is the effective spatial resolution of PET scans?
10mm
What is the spatial resolution of fMRI?
1mm
What is HRF?
Haemodynamic response function, describes the changes of the BOLD signal over time.
What is BOLD?
blood oxygen-level –dependent contrast, is the signal measured in fMRI that relates to the concentration of oxy- and deoxyhaemoglobin in the blood.
