Cognitive PsychologyPSYC231

Cognition and the Brain:

Basic Principles 2

Dr. Jan Lauwereyns, EA619, ext. 5042

Broca:Production,Syntax

Wernicke:Comprehension,Meaning

Figure 2.22 (p. 46)(a) When a monkey is looking at the X and is not paying attention to the flashing light that is off to the side, a neuron in the cortex fires slowly; (b) when the monkey pays attention to the light (while still looking at the X) firing of the neuron increases.

Techniques for Studying the Physiology of Cognition

Electrical recording techniques

Human electrophysiology

• Electro-encephalo-graphy (E.E.G.): e.g., used for detecting different sleep phases

• Recording electrical signal from the scalp• Faint, noisy• Moderate spatial resolution, but very accurate

temporal resolution (ms)• Can be used for cognitive experiments: ERP

– Averaging– Relating to events: “Event-Related Potential”

Less popular now, but…

• ERP research was very popular in the 80s and early 90s, now losing momentum

• Related technique of MEG (magneto-encephalo-graphy), better spatial resolution but too expensive

Invasive techniques

• Electrode in the brain

Deep-brain stimulation in patients with Parkinson’s disease

Self-stimulation of subthalamic nucleus (in the basal ganglia): Patients can move

their arms and legs again

Animal models

• Single-unit studies, recording electrical discharges of individual neurons

• Cat (Hubel & Wiesel)• Monkey• Rat• Correlate neuronal activity with task events in

simple behavioural paradigms• Best possible temporal and spatial resolution• But: cost, external validity• Well defined, hypothesis driven

Neural robotics: Miguel Nicolelis

Functional imaging studies

• Functional imaging: record brain activity during task performance

• As opposed to Structural imaging, measuring tissue density only (for diagnostic purposes)

• Put S in scanner, the whole brain lights up• Data are only as good as the logic of the

experiment – this is where Psychology steps in• Subtraction method with task components• Let’s look at “spec sheet” of PET and fMRI…

Positron Emission Tomography (PET)

• Inject radioactively tagged substance (e.g., O2, glucose)

• Map the uptake of the substance (photocells)

Pro’s and con’s of PET

• Not only cerebral blood flow:– Example: Koepp et al,

1998, Nature: Measure dopamine release while participants play a video game (reduced binding in ventral striatum)

• Drawbacks: – involves radiation– poor temporal resolution

(tens of seconds, minutes)

functional Magnetic Resonance Imaging (fMRI)

• Map rates of O2 uptake

– Loss of O2 causes magnetic changes to blood

– Non-invasive

Most important pro:– Temporal resolution better– With the most powerful scanners it is possible to map

changes in blood flow in a few seconds (event fMRI)

But:

– Noise: even small movements (eye blink)– Requires averaging across samples– Problems with inter-individual differences– Preferably multiple samples from the same S

Doesn’t come cheap…

Transcranial magnetic stimulation

• Deliver a fairly localized magnetic current while participants perform a task

• Not really “invasive” in the sense that nothing mechanical is put in the brain

• Long-term effects not known

Lesion or subtraction method(Neuropsychology)

• Dr. Carolyn Wilshire• Patients with specific brain

damage• Compared with normals• How do the patients perform differently in

behavioral/cognitive tests?• Single or double dissociation (broken TVs)

• No control over size and site of damage• Animal models