PSYCH 202: Methods to Study the Brain

EEG

records the electrical activity of the brain from electrodes placed on the scalp

• electroencephalography

EEG How is it recorded?

Electrodes are placed on the scalp (e.g., 128-electrode EGI net) to measure electrical activity produced by large populations of neurons

EEG advantages

Excellent temporal resolution (milliseconds)

• allows researchers to determine when cognitive processes occur

EEG limitations

Poor spatial resolution because electrical signals are distorted as they pass through the skull and scalp

EEG Clinical uses of EEG

• Assessing brain states (e.g., coma vs unconsciousness)

• Locating epileptic seizure foci

EEG What is an Event-Related Potential (ERP)

The averaged EEG response time-locked to a specific event or stimulus

EEG Why is trial averaging used in ERP research

To remove background EEG activity and isolate the brain’s response to a specific stimulus

EEG What information do ERP components provide

They reveal the timing and stages of cognitive processing

EEG What does the N1 ERP component represent

Early sensory processing approximately 100 ms after stimulus onset

EEG What does the amplitude of an ERP component indicate

The amount of strength of processing occurring at that stage

EEG What question is EEG/ERP best suited to answer

“when does a cognitive process occur”

EEG What are neural oscillations

Rhythmic patterns of brain activity occurring at different frequencies

EEG What frequency range defines Delta oscillations

Less than 4 Hz

EEG What frequency range defines Theta oscillations

4-7 Hz

EEG What frequency range defines Alpha oscillations

8-14 Hz

EEG What frequency range defines Beta oscillations

15-30 Hz

EEG What frequency range defines Gamma oscillations

30-60 Hz

EEG What cognitive process is often associated with Gamma oscillations

Visual processing

EEG What cognitive process is commonly associated with Theta oscillations

Working memory

EEG What is Fast Fourier Transform (FFT)

A mathematical technique used to decompose EEG signals into different frequency components

EEG What characteristic pattern is typically observed in FFT power spectra

A 1/f relationship where lower frequencies have greater power

EEG What is the limitation of FFT analysis

Poor temporal resolution

EEG What advantage do time-frequency plots have over FFTs

They show how oscillatory activity changes over time

EEG What oscillation is commonly observed during WM retention

Frontal midline theta

EEG Which brain region shows the strongest theta activity during WM tasks

Frontal cortex

MEG measures

magnetic fields generated by synchronously active neurons

• Magnetoencephalography

MEG How does it differ from EEG

EEG measures electrical activity, whereas MEG measures magnetic activity

MEG Why does it provide better localisation than EEG

Magnetic fields are less distorted by the skull and scalp

MEG major advantage

Excellent temporal resolution with improved spatial localisation compared to EEG

MEG what are SQUIDS

Superconducting Quantum Interference Devices used to detect exremely small magnetic fields produced by the brain

MEG disadvantages

Expensive

• SQUIDs require liquid helium cooling and magnetically shielded rooms

MEG What are OPMS (Optically Pumped Magnetometers)

Newer MEG sensors that operate at room temperature and may reduce costs

MEG what type of brain activity is MEG most sensitive to

Activity occurring in cortical sulci

MEG What additonal information can MEG provide beyond localisation

Functional connectivity between brain regions

MEG why is it often combined with MRI

MRI provides anatomical info that improves source localisation

TMS

A technique that uses magnetic fields to stimulate or temporarily disrupt activity in targeted brain regions

• Transcranial Magnetic Stimulation

TMS How does it work?

Electrical current flowing through a coil creates a magnetic field that induces current in the brain

TMS Why is it called a “virtual lesion” technique

Because it can temporarily disrupt normal function in a brain without causing permanent damage

TMS What is the primary use of TMS in cognitive neuroscience

Determining whether a brain region is causally involved in a cognitive process

TMS What Q does it answer that fMRI cannot

Whether a brain region is necessary for a task rather than simply active during it

TMS What are Motor-Evoked Potentials (MEPs)

Muscle responses produced when TMS stimulates the motor cortex

TMS What can MEPs be used to access

Motor cortex excitability

MRI

A brain imaging technique that uses magnetic fields and radiofrequency pulses to create detailed anatomical images

• magnetic resonance imaging

MRI What particles are manipulated during MRI?

Hydrogen protons

MRI What happens to protons inside a strong magnetic field

They align with the magnetic field

MRI What happens when a radiofrequency pulse is applied

Protons are displaced from alignment and later release energy as they realign

MRI What creates MRI image contrast

Different tissues release different amounts of energy

MRI What does structural MRI measure

Anatomical brain structure

MRI How does functional MRI distinguish grey matter from white matter

They release different amounts of radiofrequency energy

MRI What is the major strength of structural MRI

Excellent spatial resolution

fMRI What does it measure

Changes in oxygenated blood flow associated with neural activity

fMRI What BOLD stand for

Blood Oxygen Level Dependent signal

fMRI Why does blood flow increase to active brain regions

Active neurons require more oxygen and energy

fMRI What does stronger BOLD signal indicate

Increased neural activity in that region

fMRI What is the temporal resolution of fMRI

seconds

fMRI What is the spatial resolution of fMRI

~3-6mm

fMRI strength

excellent spatial localisation

fMRI limitation

Poor temporal resolution because blood flow changes occur slowly

fMRI What does the subtraction method in fMRI involve

Comparing an experimental condition within a control condition to identify task-related activity

DTI

An MRI-based technique that measures the diffusion of water molecules to map white matter pathways

• Diffusion Tensor Imaging

DTI Why can DTI track fibre tracts?

Water diffuses more easily along axons than across them

DTI What is isotropic diffusion

Water moves equally in all directions

DTI What is anisotropic diffusion

Water moves preferentially in one direction, typically along axons

DTI What is tractography

Reconstruction of white matter pathways using diffusion data

DTI What is the primary use of DTI

Mapping structural connectivity between brain regions

DTI What was a limitation of early DTI techniques

Difficulty resolving crossing fibre tracts

PET

A brain imaging technique that measures the distribution of radioactive tracers within the brain

• Positron Emission Tomograohy

PETHow does it work

A radioactive ligand (e.g., glucose) is injected into the bloodstream and accumulates in metabolically active brain regions

PET Why do active brain areas accumulate more tracer

They have greater metabolic demands and consume more glucose and oxygen

PET Spatial resolution

1 cm

PET Temporal resolution

Poor (about 1 minute or longer)

PET Major strength

Ability to image metabolism and specific neurochemical systems

Which technique has the best temporal resolution?

EEG and MEG

Which technique has the best spatial resolution?

Structural MRI and fMRI

Which technique provides causal evidence about brain function?

TMS

Which technique is best for studying white matter pathways?

DTI tractography

Which technique is best for studying neurotransmitter systems?

PET

Why are multiple neuroimaging techniques often combined?

To combine strengths (e.g., EEG/MEG for timing and MRI/fMRI for localization).