Methods

METHODS OF COGNITIVE NEUROSCIENCE

1). Brain Lesions:

- Natural occurring trauma/disease that affected the brain (neurological dysfunctions, epilepsy, car accidents, stroke,

tumors, or neurodegenerative diseases, such as Alzheimer's disease)

- Lead to either a Closed or an Open Head Injury

- Advantages: allows a specific brain region to be directly linked to a specific aspect of mental function. Can tell us if a

brain area is critical for a particular function.

- But: damage may be hard to localize; not sure about the functional specificity of the lesioned region

2). Temporary Lesions- Stimulation Methods

Transcranial Magnetic Stimulation (TMS)/Transcranial Direct Current Stimulation (tDCS):

- Produce change in neuronal firing patterns

- Advantages: non-invasive, allows specificity in the deficit produced and strict experimental control,

causality, some suggestion of beneficial effects (e.g. in depression)

- Caveats: stimulation is mild, restrictions in subject population

3). Brain Imaging Methods: difference between structural and functional techniques, general principles of each technique.

Structural methods: Image the different anatomical structures inside the brain in a static fashion; No requirement for

temporal resolution but high demands for spatial resolution

CAT scan (Computerized Axial Tomography) or CT

- X-rays get projected through the head; the intervening tissue absorbs some of them (bone, blood and

neural tissues have different densities). Receptors on the other side of the head detect the attenuated X-

rays that have passed through → able to create 2D images.

- Advantages: : can image bone, blood, and neural tissue

- Caveats: Less spatial resolution than MRI, and it may be harmful (especially for pregnant women and

children)

Structural Magnetic Resonance Imaging (MRI or sMRI)

- Source of MRI signal: hydrogen nuclei or protons found in water molecules. Signal depends on the

differences in the magnetic properties of organic tissue (e.g., density of hydrogen atoms is different

in gray and white matter)→ able to differentiate them on MRI images.

- Advantages: Non-invasive (no radiation); Very good spatial resolution (even sub-mm); can visualize

changes that occur in many neurological diseases (epilepsy, Alzheimer's). Several types of signals can be imaged; easy to

distinguish gray and white matter.

- Disadvantages: Bulky and expensive; Some subjects cannot undergo MRI. e.g.: Claustrophobia; Metal implants in the

Functional methods: Image the brain activity in a dynamic fashion; require better temporal resolution and spatial resolution

as well. Capitalizing on metabolic changes correlated with neural activity.

EEG (electroencephalography). Continuous recording of overall brain activity.

- Signals: Fluctuating voltage at each electrode is compared to the voltage at a reference electrode.

Records the electrical activity of the brain that results from neuronal firing.

- Advantages: EEG patterns are well established and consistent among individuals => EEG recordings

detects abnormalities in brain function: commonly used to diagnose epilepsy, which causes abnormalities

in the EEG readings.

- Limitation: Not as useful for cognitive neuroscience (records global electrical activity)

Event-related brain potentials (ERPs):

- Records electrical activity time-locked to specific events, in the form of small, event-related

signals embedded in ongoing EEG. Averaging of EEG signals

- Provides information about WHEN processes occur in the brain

- Advantages: Direct (measure neuronal activity), Non-invasive, very good temporal resolution

(ms), Relatively inexpensive, Not many limitations in the possible experimental paradigms,

supported by well-known components

- Disadvantage: poor spatial resolution (cm or more)

Functional Magnetic Resonance Imaging (fMRI)

- Depends on the magnetic properties of oxygenated and deoxygenated hemoglobin. Signal: Blood

Oxygenation Level Dependend (BOLD) changes in the brain while a participant is performing a task (Ex:

watching different types of images).

- More neural activity → more oxyHb is supplied flushing away de-oxyHb → larger the ratio of oxyHb and

de-oxyHb → Stronger BOLD response

- Measures change in BOLD response over time in response to a stimulus. Compares the BOLD signals in response to

experimentally manipulated events with control conditions, able to know which regions are more active for these events.

-Advantage: Non-invasive, very good spatial resolution Disadvantages: Indirect measure of neuronal activity

(hemodynamics), poor temporal resolution (seconds), expensive