Global Brain Activity

Question 1

What is EEG?

Answer 1

• An electroencephalogram (EEG) is a recording of brain activity.
• Used clinically to study physiology of sleep and epilepy

Question 2

• An electroencephalogram (EEG) is a recording of brain activity.
• Used clinically to study physiology of … and also …

Answer 2

• 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

Question 3

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.

Answer 3

• It takes many thousands of underlying neurons, activated together, to generate an EEG signal big enough to see at all.

Question 4

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.

Answer 4

• 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.

Question 5

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.

Answer 5

• 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.

Question 6

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.

Answer 6

• 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.

Question 7

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

Answer 7

• 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

Question 8

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

Answer 8

• 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

Question 9

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

Answer 9

• 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

Question 10

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

Answer 10

• 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

Question 11

Sleep: behavioural criteria

• … motor activity
• … response to stimulation
• Stereotypic …
• Relatively easy …
• About 1/… of life sleeping

Answer 11

• Reduced motor activity
• Decreased response to stimulation
• Stereotypic postures
• Relatively easy reversibility
• About 1/3 of life sleeping

Question 12

Sleep: behavioural criteria

• Reduced … activity
• Decreased response to …
• … postures
• Relatively … reversibility
• About 1/… of life sleeping

Answer 12

• Reduced motor activity
• Decreased response to stimulation
• Stereotypic postures
• Relatively easy reversibility
• About 1/3 of life sleeping

Question 13

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

Answer 13

• 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

Question 14

Three functional states of sleep

• 3 functional states: these are…

Answer 14

• 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

Question 15

Summary scheme of sleep-wake states

Answer 15

Question 16

Functions of sleep and dreaming

• Conserve of metabolic …
• Cognition
• …regulation
• Neural … and mental …

Answer 16

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

Question 17

Functions of sleep and dreaming

• Conserve of … energy
• C…
• T…
• … maturation and mental health

Answer 17

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

Question 18

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

Answer 18

• 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

Question 19

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
  • …

Answer 19

• 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

Question 20

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

Answer 20

• 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

Question 21

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)

Answer 21

• 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)

Question 22

Sequence of events in the acquisition of an MRI scan

Answer 22

Question 23

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

Answer 23

• 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

Question 24

PET image

Answer 24

measures change of blood flow to a region

Question 25

fMRI

Answer 25

• sensitive to the concentration of oxygen in the blood

Question 26

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

Answer 26

• 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

Question 27

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

Answer 27

• 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

Question 28

• … 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

Answer 28

• 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

Question 29

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).

Answer 29

• 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).

Question 30

Spatial and temporal resolution

Answer 30