Global brain activity Flashcards
Brain rhythms (sleeping and waking) and breathing cycles (such as steps in walking, stages of night sleep) are essential for life. What was discovered by Hans Berger (1929)?
What is special about the Beta rhythm?
Discovered the basic a-wave
- Responsible for sitting with eyes closed
Used in usual involvement.
-Same brain activity as REM (dream) sleep
Describe the use of an electroencephalogram.
Consider what it measures, advantages and disadvantages
EEG measures surface waves. Aids in: -Correlate with pathology and behavioral states -Physiology of sleep -Epilepsy
Advantages:
Safe, widely available, non-invasive, good temporal resolution
Disadvantages:
Poor spatial resolution (knowing where the signal is coming from, receptors getting signals from several centimetres below –> summation)
How do EEG’s work?
(Think about what is being measured and the requirements for signal detection)
What is meant by synchronous activity and why is it relevant?
Constant flow of current from IPSC and EPSC’s generate small fields in pyramidal cells
Requirements for signal detection:
- Whole population of neurons active in SYNCHRONY to generate a large enough electric 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
The amplitude of the EEG signal partly depends on how synchronous the activity of the underlying neurons is.
-Depends on the number of active cells, the total amount of excitation and timing of activity
Outline the different stages of non-REM sleep
Stage 1 non-REM sleep: from thalamus, synchronous
Stage 2 non-REM sleep: even more synchronous
Stage 3 non-REM sleep: increased amplitude, decreased frequency of delta rhythms
Stage 4 non-REM sleep: amplitude even more pronounced and even fewer delta rhythms
Consider how synch rhythms are generated
Thalamus has some pacemaker cells which set the tone
(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 synchronized with many other thalamic cells via a ‘hand-clapping kind of collective interaction.
All neurons have a fixed physiological range for which they can fire, therefore synchronous activity can occur by chance within this range
Cortex follows what the thalamus dictates
What are the functions of brain rhythms?
- Sensory input
- Activity coordination of different cortical regions (oscillations, synchrony)
- Are they meaningless? By-product of feedback circuits and connections
- UNKNOWN
State the behavioral criteria for sleep
Which neurotransmitters are involved in sleep?
- Reduced motor activity
- Decreased response to stimulation
- Stereotypic postures
- Relatively easily reversible
AWAKE NON REM(Stages 1-4) REM SLEEP
Serotonin, dopamine, ACh
Why do we sleep? Dream?
- Conservation of metabolic energy
- Cognition
- Thermoregulation
- Neural maturation and mental health
Describe the structural imaging available to look at global brain activity
Structural imaging measures spatial configuration of types of tissues in the brain
-It is static
e.g.
CT- White and grey matter not very well distinguished
MRI- Slower, more expensive, good resolution. Can see bone, meninges and parenchyma
How do CT scans work?
Indication?
Based on amount of X-ray absorbed in different types of tissue
-Bone absorbs the most (appears whitest), CSF absorbs the least (ventricles appear black) and parenchyma intermediate
Used in clinical settings to diagnose tumors or identify hemorrhaging (as in hemorrhagic or ischaemic stoke)
In which ways are MRIs better than CT scans?
Completely safe so people can be repeatedly scanned
Better spatial resolution
Better discrimination between white and grey matter
Can be adapted for detecting the changes in blood oxygenation associated with neural activity (fMRI
Describe the functional imaging available to look at global brain activity
Functional imaging measures movement-to-movement variable characteristic of brain that may be associated with changes in cognitive processing. IT ALWAYS MEASURES RELATIVE CHANGES IN ACTIVITY
DYNAMIC
e.g. PET, fMRI
Outline the sequence of events in the acquisition of an MRI scan
Magnetic fields of protons-initially random
Add external magnetic fields(3Tesla… comparison to earths magnetic field of 1microTesla) and some protons align.
Brief radio wave pulse orients them to 90 degrees (spin) and produces a measurable MR signal. The protons return back (relax) and a new brain slice is scanned
Describe the physiology underpinning functional imaging
Brain (2% of body mass) accounts for 20% of oxygen uptake. It can’t store oxygen and only stores little glucose
Oxygen and glucose demand must be met. When metabolic activity of neutrons increases, blood supply follows
PET measures changed of blood flow to a region
fMRI is sensitive to the concentration of oxygen in the blood
Because of constant activity, we always compare an experimental condition with a baseline condition (named before and during performance)
This indirectly measures neuronal activity
How does PET scanning work?
- Based on blood volume
- Involves radioactivity (signal depends on radioactive tracer)
- Participants scanned once or few times
- Temporal resolution: 30”
- Effective spatial resolution: 10mm
- Sensitive to the whole brain
- Can use pharmacological tracers
