Global Brain Activity Flashcards
What is EEG?
- An electroencephalogram (EEG) is a recording of brain activity.
- Used clinically to study physiology of sleep and epilepy
- An electroencephalogram (EEG) is a recording of brain activity.
- Used clinically to study physiology of … and also …
- An electroencephalogram (EEG) is a recording of brain activity.
- Used clinically to study physiology of sleep and epilepy
- Non invasive - children and adults
- Electrodes applied - standard positions - study activity of neurons - good temporal resolution
- Poor spatial resolution - cant tell a signal apart if too close
- Surface of cerebral cortex mainly
- Electrodes named depending on location on scalp

Generation of small fields in pyramidal cells
- It takes many thousands of underlying neurons, activated together, to generate an … signal big enough to see at all.
- It takes many thousands of underlying neurons, activated together, to generate an EEG signal big enough to see at all.

The Electroencephalogram (EEG)
- Basic requirements for signal detection:
- A whole population of neurons must be active in … to generate a large enough electrical field at the level of the scalp
- This population of neurons must be aligned in a … orientation so that they can summate rather than cancel out.
- 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 that they can summate rather than cancel out.

The Electroencephalogram (EEG)
- Basic requirements for signal detection:
- A whole population of … 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 can … rather than cancel out.
- 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 that they can summate rather than cancel out.

Synchronous activity
- The amplitude of the EEG signal partly depends on how … the activity of the underlying neurons is.
- Number of active cells, total amount of …, timing of activity.
- The amplitude of the EEG signal partly depends on how synchronous the activity of the underlying neurons is.
- Number of active cells, total amount of excitation, timing of activity.

EEG / brain rhythms correlate with pathology & behavioural states
- Left - EEG during … … - higher amplitude signal along all electrodes - large signal starts at ends at same time
- Right - … EEG - based on whether they are awake with eyes closed - left, or awake with eyes open - right
- … sleep - beta rhythms - dreaming and mental activity
- Non … - deep stage - higher amplitude signal

- Left - EEG during epileptic seizure - higher amplitude signal along all electrodes - large signal starts at ends at same time
- Right - normal EEG - based on whether they are awake with eyes closed - left, or awake with eyes open - right
- REM sleep - beta rhythms - dreaming and mental activity
- Non Rem - deep stage - higher amplitude signal
Generation of synchronous rhythms
- 2 mechanisms:
- … neuron - gives pace
- OR … - interact dynamically
- Right picture - thalamus sends specific signals out - rhythm inputs towards cortex - large network of cells fire same frequency - synchronous activity

- 2 mechanisms:
- Pacemaker neuron - gives pace
- OR improvisation - interact dynamically
- Right picture - thalamus sends specific signals out - rhythm inputs towards cortex - large network of cells fire same frequency - synchronous activity
- Generated - pacemaker cells in thalamus
Generation of synchronous rhythms
- A one neuron oscillator
- … 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 … pacemaker neuron then becomes synchronised with many other … cells via a hand-clapping kind of collective interaction
- A one neuron oscillator
- 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 via a hand-clapping kind of collective interaction

Functions of Brain Rhythms?
- Theories:
- Sensory input – thalamus – cortex
- Activity … (binding) of different cortical regions (synchrony, oscillations)
- OR
- … by-product of feedback circuits and connections
- Overall - … rhythms give us a window of the functional states of the brain
- Sensory input – thalamus – cortex
- Activity coordination (binding) of different cortical regions (synchrony, oscillations
- Meaningless by-product of feedback circuits and connections
- Overall - EEG rhythms give us a window of the functional states of the brain
Sleep: behavioural criteria
- … motor activity
- … response to stimulation
- Stereotypic …
- Relatively easy …
- About 1/… of life sleeping
- Reduced motor activity
- Decreased response to stimulation
- Stereotypic postures
- Relatively easy reversibility
- About 1/3 of life sleeping
Sleep: behavioural criteria
- Reduced … activity
- Decreased response to …
- … postures
- Relatively … reversibility
- About 1/… of life sleeping
- Reduced motor activity
- Decreased response to stimulation
- Stereotypic postures
- Relatively easy reversibility
- About 1/3 of life sleeping
Three functional states of sleep
- 3 functional states:
- … - low amplitude signal, high frequency
- …-… - 4 stages
- Stage 1 - move and change posture but brain largely not connected to environment, thalamic activity dominates cortical activity
- Stage 2 onwards – more synchronous - More deep sleep - more dominated by thalamic inputs
- Stage 3 and 4 – … rhythms
- … – active hallucinating brain, paralysed body (lucid dream) exception of breathing muscles and some small muscles and eyes
- 3 functional states:
- Awake - low amplitude signal, high frequency
-
Non-REM - 4 stages
- Stage 1 - move and change posture but brain largely not connected to environment, thalamic activity dominates cortical activity
- Stage 2 onwards – more synchronous - More deep sleep - more dominated by thalamic inputs
- Stage 3 and 4 – delta rhythms
- REM – rapid eye movement - active hallucinating brain, paralysed body (lucid dream) exception of breathing muscles and some small muscles and eyes
Three functional states of sleep
- 3 functional states: these are…
- 3 functional states:
- Awake - low amplitude signal, high frequency
-
Non-REM - 4 stages
- Stage 1 - move and change posture but brain largely not connected to environment, thalamic activity dominates cortical activity
- Stage 2 onwards – more synchronous - More deep sleep - more dominated by thalamic inputs
- Stage 3 and 4 – delta rhythms
- REM – rapid eye movement - active hallucinating brain, paralysed body (lucid dream) exception of breathing muscles and some small muscles and eyes
Summary scheme of sleep-wake states

Functions of sleep and dreaming
- Conserve of metabolic …
- Cognition
- …regulation
- Neural … and mental …
- Conserve of metabolic energy
- Cognition
- Thermoregulation
- Neural maturation and mental health
Functions of sleep and dreaming
- Conserve of … energy
- C…
- T…
- … maturation and mental health
- Conserve of metabolic energy
- Cognition
- Thermoregulation
- Neural maturation and mental health
Imaging techniques
- … Imaging: measures of the spatial configuration of types of tissue in the brain (static maps)
- Computerised tomography - CT
- Magnetic … … - MRI
- … Imaging: measures the moment-to-moment variable characteristics of the brain that may be associated with changes in cognitive processing (Dynamic maps)
- Positron … … - PET
- Functional magnetic resonance imaging - fMRI
-
Structural Imaging: measures of the spatial configuration of types of tissue in the brain (static maps)
- Computerised tomography - CT
- Magnetic resonance imaging - MRI
-
Functional Imaging: measures the moment-to-moment variable characteristics of the brain that may be associated with changes in cognitive processing (Dynamic maps)
- Positron emission tomography - PET
- Functional magnetic resonance imaging - fMRI
Imaging techniques
- Structural Imaging: measures of the … … of types of tissue in the brain (static maps)
- …
- …
- Functional Imaging: measures the moment-to-moment variable … of the brain that may be associated with changes in …. processing (Dynamic maps)
- Positron emission tomography - PET
- …
- Structural Imaging: measures of the spatial configuration of types of tissue in the brain (static maps)
- Computerised tomography - CT
- Magnetic resonance imaging - MRI
- Functional Imaging: measures the moment-to-moment variable characteristics of the brain that may be associated with changes in cognitive processing (Dynamic maps)
- Positron emission tomography - PET
- Functional magnetic resonance imaging - fMRI
CT scans:
- Based on the amount of X-ray … in different types of tissue
- Bone absorbs the most (the skull appears …), CSF absorbs the least (ventricles appear …) and the brain matter is intermediate (…)
- Used in clinical settings, e.g. to diagnose tumours or identify haemorrhaging or other gross brain anomalies
- 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 (ventricles appear black) and the brain matter is intermediate (grey)
- Used in clinical settings, e.g. to diagnose tumours or identify haemorrhaging or other gross brain anomalies
MRI
- 2003 Nobel prize to Sir Peter Mansfield and Paul Lauterbur
- Completely …, so people can be scanned … …
- Provides a much better … resolution
- Provides better … between white and grey matter
- Can be adapted for detecting the changes in blood … associated with neural activity (fMRI)
- 2003 Nobel prize to Sir Peter Mansfield and Paul Lauterbur
- 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)
Sequence of events in the acquisition of an MRI scan

Basic Physiology underpinning functional imaging
- The brain makes up 2% of the body weight, but consumes …% of the body’s oxygen uptake; it can’t store oxygen and only stores little …
- 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.
- … measures change of blood flow to a region
- … is sensitive to the concentration of oxygen in the blood
- Because of constant activity, we always compare and experimental condition with a baseline condition (before and during performance)
- Indirect measures of neuronal activity
- 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.
- PET measures change of blood flow to a region
- fMRI is sensitive to the concentration of oxygen in the blood
- Because of constant activity, we always compare and experimental condition with a baseline condition (before and during performance)
- Indirect measures of neuronal activity
PET image
measures change of blood flow to a region

fMRI
- sensitive to the concentration of oxygen in the blood

Functional imaging - PET vs fMRI
- PET
- Based on … …
- 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
- (BOLD) fMRI
- Based on … … …
- No radioactivity (signal depends on deoxyhaemoglobin levels)
- Participants scanned … times
- Temporal resolution: 1-4”
- Spatial resolution: 1mm
- Some brain regions (e.g. near sinuses) are hard to image
- PET
- 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
- (BOLD) fMRI
- Based on blood oxygen concentration
- No radioactivity (signal depends on deoxyhaemoglobin levels)
- Participants scanned many times
- Temporal resolution: 1-4”
- Spatial resolution: 1mm
- Some brain regions (e.g. near sinuses) are hard to image
Functional imaging - PET vs fMRI
- PET
- Based on blood volume
- Involves … (signal depends on … tracer)
- Participants scanned once or few times
- … resolution: 30”
- Effective … resolution: 10mm
- Sensitive to the whole brain
- Can use pharmacological tracers
- (BOLD) fMRI
- Based on blood oxygen concentration
- No … (signal depends on deoxyhaemoglobin levels)
- Participants scanned many times
- … resolution: 1-4”
- … resolution: 1mm
- Some brain regions (e.g. near sinuses) are hard to image
- PET
- 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
- (BOLD) fMRI
- Based on blood oxygen concentration
- No radioactivity (signal depends on deoxyhaemoglobin levels)
- Participants scanned many times
- Temporal resolution: 1-4”
- Spatial resolution: 1mm
- Some brain regions (e.g. near sinuses) are hard to image
- … signal: blood oxygen-level-dependent contrast, is the signal measured in fMRI that relates to the concentration of oxy- and deoxyhaemoglobin in the blood.
- HRF - Haemodynamic response function, describes the changes of the … signal over time
- 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.
- HRF - Haemodynamic response function, describes the changes of the BOLD signal over time

Imaging techniques summary
- … 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).
- Neural activity consumes oxygen from the blood. This triggers an increase in blood flow to that region (…) and a change in the amount of deoxyhaemoglobin in that region (…).
- … imaging always measures relative changes in activity (e.g. activity while performing a task vs. baseline or a control task).
- 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).
- Neural activity consumes oxygen from the blood. This triggers an increase in blood flow to that region (PET) and a change in the amount of deoxyhaemoglobin in that region (fMRI).
- Functional imaging always measures relative changes in activity (e.g. activity while performing a task vs. baseline or a control task).
Spatial and temporal resolution
