Topic 3: Imaging the Brain

Question 1

Electroencephalography (EEG)

Answer 1

A complex electroencephalographic waveform related in time to a specific sensory event.

An Electroencephalography (EEG) is a test that measures the electrical activity in the brain. The test uses small sensors (electrodes) that are placed on the scalp to detect the electrical signals in the brain.
- These signals are then recorded and displayed as a series of waves on a computer screen.
- By measuring the electrical activity in the brain, an EEG can provide information about the function of the brain, including which parts of the brain are active and which parts are not.
- Scalp recorded (summation): big signals made by many neurons, presumably relevant to the question at hand
- First described by Berger (1929)
- Quantified in two domains: time domain and voltage

Question 2

Electroencephalography (EEG) signals are quantified in two domains:

Answer 2

The time domain and the frequency domain.

The time domain represents the EEG signal as a series of voltage measurements taken at regular intervals over time. This domain provides information about the temporal evolution of the EEG signal and can be used to identify specific events in the EEG such as the onset and offset of a particular brain wave.
- VOLTAGE

The frequency domain represents the EEG signal as a series of amplitudes and frequencies. This domain provides information about the spectral content of the EEG signal and can be used to identify specific frequency bands, such as delta, theta, alpha, beta, and gamma, that are associated with different cognitive states. By analyzing the EEG signal in the frequency domain, researchers can gain insights into the underlying neural processes that are generating the EEG signal.
- POWER (Fourier transform)

Question 3

Event-related Potentials

Answer 3

• Deflections in the EGG, not action potentials.
• ERPs are slower signals that reflect the coordinated activity of large populations of neurons.
• ERP signals can be recorded by placing electrodes on the scalp.
• An ERP reflects the sum of many action potentials that are occurring over a larger population of neurons, and it provides a more global measure of neural activity.
• time-locked activity
• neurotransmitter binding

ERPs are largely the excitatory and inhibitory graded potentials, the EPSPs and IPSPs that a sensory stimulus triggers on dendrites.

Question 4

What does “time-locked activity” refer to when speaking about Event-related potentials?

Answer 4

In the context of event-related potentials (ERPs), “time-locked activity” refers to the electrical activity in the brain that is synchronized with a specific event or stimulus. ERPs are considered time-locked because the electrical signals they measure are in synchrony with a particular event or stimulus. For example, the event might be a visual stimulus, such as a flash of light, or an auditory stimulus, such as a tone. The ERP measurement is taken after the event and shows the electrical activity that occurs in the brain in response to the event.

Question 5

What does “neurotransmitter binding” refer to when speaking about Event-related potentials?

Answer 5

“Neurotransmitter binding” refers to the process by which neurotransmitters bind to specific receptors on a neuron. This binding leads to the activation of the receptor, which in turn triggers changes in the electrical properties of the neuron, including the flow of ions into or out of the cell. When many neurons are activated in a coordinated manner in response to a specific stimulus or event, this coordinated activity can be reflected in the EEG as an event-related potential (ERP). The changes in the electrical properties of the neurons that are part of the ERP are thought to be related to the release and binding of specific neurotransmitters, so studying neurotransmitter binding can provide insights into the underlying mechanisms that give rise to ERPs.

Question 6

Exogenous EEG

Answer 6

Looking at time-locked events stimulated by something external to the body.

An exogenous EEG refers to electrical activity that is externally triggered, such as by a stimulus, sound, or movement. This type of EEG activity is used to study sensory processing and perception, as well as attention and memory processes.

Question 7

Endogenous EEG

Answer 7

Looking at time-locked events stimulated by something internally.

An endogenous EEG, on the other hand, refers to spontaneous electrical activity that is not related to an external stimulus. This type of EEG activity is used to study brain activity and function when the individual is at rest, or when they are not performing any specific task. Endogenous EEG activity is believed to reflect intrinsic brain processes, such as rhythmic activity associated with different stages of sleep.

Question 8

10-20 System

Answer 8

The 10-20 system is a standardized method for placement of electrodes on the scalp for the recording of electroencephalography (EEG) signals.
- The system is called the 10-20 system because the electrodes are placed at specific locations on the scalp that are approximately 10% or 20% of the distance from one landmark to another.

The landmarks used are:
- the nasion (the point at the bridge of the nose where the frontal and nasal bones meet),
- the inion (the bony prominence at the base of the skull),
- and the preauricular points (the points in front of the ears).

Question 9

A simple legend for remembering the subscripts in the 10-20 system:

Answer 9

Fp: Frontopolar electrodes, located near the forehead
F: Frontal electrodes, located near the forehead
C: Central electrodes, located near the midline of the head
T: Temporal electrodes, located near the temples
P: Parietal electrodes, located near the top and back of the head
O: Occipital electrodes, located near the back of the head

• An electrode labelled “Fz” has a subscript of “z,” indicating that it is located on the midline of the head, at the point where the forehead meets the scalp.
• On the right of the head = subscript with an even number
• On the left of the head = subscript with an odd number

Examples:
- Pz = parietal zero
- O1 = occipital left
- T4 = Temporal right

Question 10

What do Beta (15 Hz) waves indicate in EEG?

Answer 10

Beta waves are high-frequency (15 Hz) brain waves commonly associated with a state of alertness and focused attention. They are typically more prominent during activities that require active thought, such as problem-solving, decision-making, and planning.

• Beta waves tend to have a lower amplitude compared to alpha or delta waves
• Beta waves tend to be seen as fast, low-amplitude activity, while delta waves are seen as slow, high-amplitude activity.

Question 11

What do Alpha (9-12 Hz) waves indicate in EEG?

Answer 11

Alpha waves are lower frequency (9-12 Hz) brain waves that are typically associated with a state of relaxed, daydreaming or meditative focus. They are often more prominent when the eyes are closed, when a person is relaxed, or when they are in a state of mental detachment from their surroundings.

Question 12

What do Delta (1-4 Hz) waves indicate in EEG?

Answer 12

Delta waves are the slowest brain waves, with frequencies ranging from 1-4 Hz. They are typically associated with deep, dreamless sleep and are most prominent in infants and young children. In adults, delta waves are typically present in deep sleep and may be reduced in certain sleep disorders, such as insomnia.

Question 13

Brain Mapping with ERP: Interpret

Answer 13

• The waves correspond to successive activations of synaptic connections through the auditory pathway from brainstem to cortex.
• ERP signals identified as I through VI (roman numerals) are from brainstem signal generators (neurons in the pathway)
• Those designated N0 through P1 represent activity the from primary auditory cortex regions (A1).
• Those designated N1 through P3 are from secondary and tertiary (association) regions of the cortex.
• The dotted lines indicate brain waves associated with thought processes in response to the signal.
• Negative upwards on the y-axis

For example, P3, produced 300 ms after stimulus presentation, represents decoding the meaning of the sounds.

Question 14

Signal Averaging in EEGs

Answer 14

Signal averaging in EEG refers to a method of processing EEG data to obtain a clearer and more stable representation of the underlying brain activity.
- collect multiple EEG trials and to average their voltage signals over time to produce a single, averaged EEG trace.
- reduces noise and other random fluctuations in the data, and enhances the visibility of the underlying EEG patterns that are of interest, such as event-related potentials (ERPs).
- brain waves are unique to each individual, and there is a lot of between-subject variabilities
- all subjects typically have the same paradigm, but all look different from the average

In practice, signal averaging is performed by recording multiple trials of the same EEG response, and then superimposing these trials by taking the mean of their voltages at each sample point. The resulting averaged trace is then plotted as a function of time. This process is repeated for multiple electrodes and for multiple conditions or stimuli, to produce a series of averaged traces that can be compared to one another and to theoretical predictions.

Question 15

Between-subject variability

Answer 15

Between-subject variability refers to the differences that exist between individuals in terms of their characteristics, behaviour, or responses to stimuli. In the context of EEG, between-subject variability refers to the differences in EEG patterns and amplitudes between individuals. These differences can be due to factors such as age, gender, genetic factors, or environmental exposure.

Question 16

Interpret the phrase: “ERP can elucidate specific cognitive processes underlying overt behaviour.”

Answer 16

The phrase refers to the idea that Event-related Potentials (ERPs) can be used to reveal the underlying cognitive processes that give rise to observable behaviour. In other words, by examining the electrical activity of the brain in response to specific stimuli or tasks, researchers can gain insight into the neural processes that are involved in things like attention, memory, language, perception, and decision-making.

Question 17

Lateralized Readiness Potential (LRP)

Answer 17

The Lateralized Readiness Potential (LRP) is an event-related potential (ERP) that reflects the neural activity associated with the preparation of a voluntary movement. It is a slow, gradual shift in the electrical activity of the brain that occurs before a person makes a movement. The LRP is lateralized, meaning that it occurs more prominently on one side of the brain than the other, depending on the direction of the movement. The LRP is thought to reflect the activity of the motor cortex and other brain areas involved in preparing and executing voluntary movements.

Question 18

How are the Lateralized Readiness Potential (LRP) and the Stroop task related?

Answer 18

The Lateralized Readiness Potential (LRP) is related to the Stroop task because it is often used as a measure of the preparation for action in the Stroop task.
- Initially, it was thought that our prep happens at the perceptual level (P300) but EEG revealed otherwise.

The Stroop task is a classic example of a conflict task, where there is an interference between an automatic response and a controlled response.

In the Stroop task, the LRP provides information about the degree of preparation for a response in the Stroop task, and it is often used to study the neural processes underlying attentional control and executive function. For example, the LRP might be used to investigate the difference in preparation for action when responding to congruent versus incongruent stimuli in the Stroop task.

Question 19

Stroop Task

Answer 19

In the Stroop task, participants are asked to name the color of the ink in which words are printed, but the words themselves are color names that are either congruent or incongruent with the ink color. For example, the word “RED” might be printed in blue ink.
- the LRP might be used to investigate the difference in preparation for action when responding to congruent versus incongruent stimuli in the Stroop task.

Question 20

Computerized Axial Tomography (CAT) Scan

Answer 20

A Computerized Axial Tomography (CAT) scan, also known as a Computed Tomography (CT) scan, is a medical imaging technique that uses X-rays to produce detailed cross-sectional images of the body.

Question 21

What do the dark and light regions represent in a CT scan?

Answer 21

In a CT scan, the dark regions typically represent areas of low density or air-filled spaces (e.g., the ventricles), while the light regions represent areas of higher density, such as bones or tissues.

The brightness of a particular region in a CT scan is determined by the amount of X-rays that are absorbed by that region. When X-rays pass through soft tissues, more of them are absorbed, resulting in a darker image. When X-rays pass through bones or other dense tissues, fewer of them are absorbed, resulting in a brighter image.

Question 22

Interleaving

Answer 22

Interleaving is a technique used in CT scanning to help improve the quality of the images produced by the scan. The basic idea behind interleaving is to acquire data from multiple slices of the body at the same time.

In interleaved scanning, the CT scanner takes alternating slices of the image, rather than capturing all slices in a contiguous fashion. For example, the CT scanner might scan slice 1, then skip over slice 2 and scan slice 3, then skip over slice 4 and scan slice 5, and so on. This approach can be used to reduce motion artifact in the final image or to improve the speed of the scan.

Question 23

Magnetic Resonance Imaging (MRI)

Answer 23

Magnetic Resonance Imaging (MRI) is a non-invasive medical imaging technique that uses strong magnetic fields and radio waves to produce detailed images of the body’s internal structures. The technique works by exposing the body to a strong magnetic field, which causes the nuclei of certain atoms within the body to align in a certain direction. A radio frequency pulse is then applied, which temporarily disrupts the alignment of the nuclei. As the nuclei return to their original alignment, they emit signals that are detected by the MRI machine and used to construct images of the body. MRI can be used to visualize a wide range of tissues, including bones, muscles, organs, and blood vessels, making it a valuable tool for diagnosis and treatment planning in many medical conditions.

Question 24

Rock-table Analogy (MRI)

Answer 24

Analogy used to describe how MRI images are formed:
- In a static field, all the hydrogen atoms in the human body will align in the same direction as the magnetic field. (putting the rock on the table)
- RFs are being sent into the static field: Radiofrequency (RF) pulses are applied to the patient, causing the hydrogen atoms to change their orientation (the hydrogen atoms absorb the energy, causing this to resonate = unaligned and spinning). These changes in orientation are then detected by the MRI machine and used to produce an image. (picking up the rock)
- Turning off the RFs: hydrogen atoms will go from resonance to realignment, this process gives off electromagnetic energy which is used by the system to create the image (placing the rock on a scale)
- In the rock-table analogy, the RF pulse is like a gentle tap on the rock, causing it to move. The movement of the hydrogen atoms in response to the RF pulse is then used to produce an image.

Question 25

Radio Frequency Field Pulse Sequence: Identify the coils present

Answer 25

• (1ST MAGNET) The transmitter coil in an MRI scan generates a radio frequency (RF) signal that is used to excite the hydrogen nuclei within the body. This signal is transmitted into the body, which in turn produces a magnetic resonance signal that is picked up by the receiver coil.
• (2ND MAGNET) The receiver coil is used to detect and amplify the magnetic resonance signal, which is then processed by the computer to produce an image of the body. The transmitter coil plays an important role in generating the magnetic field that is needed for the MRI scan (image acquisition), and it is typically located close to the area of the body being imaged in order to produce a clear and accurate signal.

Question 26

Gradient Field (MRI)

Answer 26

(3RD MAGNET) The gradient field is a magnetic field that changes strength and direction in different parts of the body. This field is used to spatially encode the MR signal, which allows for the creation of images. The gradient coils are responsible for producing the gradient field by generating rapid changes in the magnetic field during the imaging sequence.

Question 27

Anatomical imaging techniques

Answer 27

Anatomical imaging techniques and machines are used to visualize the structure of the body, including:
- Computed Tomography (CT) scans
- Magnetic Resonance Imaging (MRI)
- Positron Emission Tomography (PET)
- Single-Photon Emission Computed Tomography (SPECT)
- X-rays

Question 28

Functional imaging techniques

Answer 28

functional imaging techniques and machines are used to visualize the function of the body, including:
- Functional Magnetic Resonance Imaging (fMRI)
- Positron Emission Tomography (PET)
- Single-Photon Emission Computed Tomography (SPECT)
- Electroencephalography (EEG)
- Magnetoencephalography (MEG)

Question 29

The First “Functional Brain Experiment”

Answer 29

The experiment was conducted by Italian physiologist Angelo Mosso in the late 19th century and involved a patient lying on a balanced table.
- Change in the distribution of blood b/c neurons need O2 when they are active.

The table was designed in such a way that it could pivot about its center, and the patient’s head was positioned over one end of the table, while their feet were positioned over the other end. Mosso then measured the changes in the center of gravity of the table as the patient performed various mental tasks, such as reading, writing, and solving arithmetic problems.

Mosso found that there were changes in the center of gravity of the table that were associated with different mental tasks. He interpreted these changes as reflecting changes in blood flow to different parts of the brain, and concluded that different mental processes must be localized to different parts of the brain.

Question 30

Positron Emission Tomography (PET)

Answer 30

Positron Emission Tomography (PET) is a type of imaging technology that uses radioactive isotopes and a specialized camera to produce detailed images of the functional activity in the body. The patient is injected with a small amount of radioactive material, which emits positrons (positively charged particles) as it decays. When the positrons collide with electrons in the body, gamma rays are emitted, which are detected by the PET camera. This information is used to construct images of the distribution of the radioactive material in the body, and the metabolic activity of different tissues.

Simpler: The doctor will give you a tiny amount of a special substance to drink or inject into your body. This substance contains a small amount of radioactive material, which is completely safe. The radioactive material travels through your body and collects in the areas that are working the hardest. Then, when you lay down on a table, the detectors and camera will pick up the signals from the radioactive material, and turn them into a special picture.

Question 31

How are PET activation, subtraction, and averaging processes used in Positron Emission Tomography (PET):

Answer 31

PET activation: This is the process of creating a PET scan while the patient is performing a task or being exposed to a stimulus. This allows the scientists to observe changes in brain activity and see which areas of the brain are involved in the task or response.

PET subtraction: In this process, the activation scan is subtracted from a control scan to highlight the differences in brain activity between the two. This helps to eliminate background activity and clearly show which areas are specifically involved in the task or response.

PET averaging: This is a method of analyzing multiple PET scans to identify patterns of activity across participants. This can help to identify consistent patterns of brain activity and increase the reliability of the results.

Question 32

functional Magnetic Resonance Imaging (fMRI)

Answer 32

fMRI stands for functional Magnetic Resonance Imaging. It is a type of medical imaging that measures changes in blood flow in the brain to determine which areas of the brain are active. The basic principle behind fMRI is that when a brain region is activated during a cognitive task, it requires more oxygen and nutrients to perform that task. This increased demand leads to an increase in blood flow to that area.

Question 33

What is the difference between an fMRI and an MRI?

Answer 33

fMRI (functional Magnetic Resonance Imaging) is a type of functional imaging that allows researchers to study brain activity by measuring changes in blood flow and oxygenation levels in the brain. fMRI is a non-invasive imaging technique that measures changes in blood flow in response to neural activity, which provides information about brain function. MRI (Magnetic Resonance Imaging), on the other hand, is a type of structural imaging that provides high-resolution images of the brain’s anatomy and structure. MRI can be used to study both normal and abnormal brain structures, and is often used to diagnose neurological and other medical conditions.

Question 34

BOLD Signal

Answer 34

In the context of functional magnetic resonance imaging (fMRI), the blood-oxygen-level dependent (BOLD) signal is used as a proxy for changes in neural activity. It is based on the principle that neural activity is associated with changes in blood flow, which can be detected using MRI. Specifically, the BOLD signal is based on the magnetic properties of oxygen-rich blood compared to oxygen-poor blood. When there is increased neural activity in a specific brain region, the associated increased blood flow leads to an increased concentration of oxygen-rich blood in that region, which can be detected as an increase in the BOLD signal. By mapping these changes in the BOLD signal across the brain, researchers can construct images of neural activity and use these images to study brain function and make inferences about cognition, behavior, and other aspects of brain function.

Question 35

How is the “flickering checkerboard” a tool for studying brain function?

Answer 35

The “flickering checkerboard” is a commonly used stimulus in functional magnetic resonance imaging (fMRI) studies. In these studies, a checkerboard pattern is displayed on a screen in front of the subject, and the contrast between the black and white squares is alternated (or “flickered”) at a specified frequency. This creates a controlled, repeating stimulus that can be used to study brain activity in response to visual input.

The flickering checkerboard is used to study the visual cortex, which is the part of the brain that processes visual information. By flickering the checkerboard, researchers can elicit a response in the visual cortex and measure the changes in blood flow and oxygenation that occur. By comparing the response in different regions of the brain, researchers can study the neural networks that underlie visual perception and how different parts of the brain interact.