W11- Methods

What is a lesion study?

A method that investigates the effects of brain damage on cognition and behaviour to infer the function of the damaged brain region.

What is the logic behind lesion studies?

If damage to a brain area causes loss of a function, that area is likely necessary for that function.

What is the main strength of lesion studies?

They provide strong causal evidence about brain-behaviour relationships.

What is a single dissociation?

When a patient is impaired on one task but performs normally on another task.

Why is a single dissociation considered weak evidence?

The impaired task may simply be more difficult than the spared task.

What is a double dissociation?

When one patient is impaired on Task A but not Task B, while another patient shows the opposite pattern.

Why is a double dissociation important?

It provides strong evidence that two cognitive functions rely on separate neural systems.

What is a stroke?

A blockage of blood supply to the brain causing neuronal death.

What is ischaemia?

A reduction in blood supply to the brain that can impair function.

What is an aneurysm?

A weakened blood vessel that can rupture and damage brain tissue.

What is a tumour?

An abnormal growth of tissue that can damage or compress brain regions.

Why are degenerative disorders problematic for lesion studies?

They often produce widespread rather than focal damage.

What does CT stand for?

Computed Tomography.

What does CT measure?

Brain structure.

How does CT work?

Multiple X-rays are taken from different angles and combined into a 3D image.

What are the main strengths of CT?

Fast, widely available, useful for detecting strokes, bleeding, and tumours.

What is the main limitation of CT?

Relatively poor spatial resolution (~1 cm).

Why is CT considered invasive?

It exposes participants to ionising radiation.

What does MRI stand for?

Magnetic Resonance Imaging.

What does MRI measure?

Brain structure.

How does MRI work?

It measures signals from hydrogen atoms that are aligned and disturbed by magnetic fields and radio waves.

What is the approximate spatial resolution of MRI?

About 1 mm.

Why is MRI superior to CT for structural imaging?

It has much better spatial resolution and tissue contrast.

What are the main limitations of MRI?

Expensive, slow, and provides no functional information.

What does fMRI stand for?

Functional Magnetic Resonance Imaging.

What does fMRI measure?

Changes in blood oxygenation associated with neural activity.

What does BOLD stand for?

Blood Oxygenation Level Dependent signal.

Why is fMRI an indirect measure of neural activity?

It measures blood flow changes rather than neurons firing directly.

What is the main strength of fMRI?

Excellent spatial resolution.

What is the main weakness of fMRI?

Poor temporal resolution due to the delayed haemodynamic response.

Why is fMRI considered correlational?

It shows which regions are active but cannot prove those regions are necessary for a function.

What does PET stand for?

Positron Emission Tomography.

What does PET measure?

Brain metabolism and blood flow using radioactive tracers.

How does PET work?

A radioactive tracer is injected and accumulates in active brain regions, where its decay is detected by the scanner.

What is a major advantage of PET?

It can track specific substances such as neurotransmitters and receptor systems.

What is the major limitation of PET?

It requires radioactive injections.

How does PET compare with fMRI in spatial resolution?

PET has poorer spatial resolution than fMRI.

How does PET compare with fMRI in temporal resolution?

PET has much poorer temporal resolution than fMRI.

What does EEG stand for?

Electroencephalography.

What does EEG measure?

Electrical activity generated by populations of neurons.

Is EEG a direct or indirect measure of neural activity?

Direct.

What is the major strength of EEG?

Excellent temporal resolution (~1 ms).

What is the major weakness of EEG?

Poor spatial resolution.

What does MEG stand for?

Magnetoencephalography.

What does MEG measure?

Magnetic fields produced by neural activity.

Is MEG a direct or indirect measure of neural activity?

Direct.

How is MEG similar to EEG?

Both measure neural activity directly and have excellent temporal resolution.

What is an ERP?

Event-Related Potential; an averaged EEG response to a specific event or stimulus.

Why are ERPs averaged across many trials?

To reduce noise and isolate the brain response associated with the event.

What does the 'N' in an ERP component mean?

A negative voltage deflection.

What does the 'P' in an ERP component mean?

A positive voltage deflection.

What does the number in an ERP component indicate?

The approximate latency in milliseconds after stimulus onset.

What three features are used to describe ERP components?

Latency, amplitude, and polarity.

What is an ERF?

Event-Related Field; the MEG equivalent of an ERP.

What is the inverse problem?

The difficulty of determining the exact neural source that generated a scalp-recorded EEG or MEG signal.

Why do EEG and MEG have poor spatial resolution?

Many different brain sources can produce similar signals at the scalp.

Which methods provide the best temporal resolution?

EEG and MEG.

Which method provides the best structural spatial resolution?

MRI.

Which method is most commonly used to identify active brain regions during cognition?

fMRI.

Which methods provide strong causal evidence?

Lesion studies.

Which methods are primarily correlational?

CT, MRI, fMRI, PET, EEG, MEG, ERP, and ERF.