PS4529/30PS4529/30ApplicationsApplicationsof Cognitiveof CognitiveNeuroscienceNeuroscience

Lectures 7/8 – where is my mind?

Lectures 9/10 – what is episodic Memory?

Lecture 11/12 – Cognitive neuroscience in the courtroom: the special case of episodic memory.

Key concepts that underpin Cognitive Neuroscience

Electrophysiological

Haemodynamic

Psychophysiology

• Aim is to develop mind reading technologies

• We are most interested in the PPY of Perception and Cognition. In other words, Cognitive Neuroscience

• Can we tell what a person is thinking or experiencing just by looking at their brain activity?

Phrenology Was Odd…

• There is no known mechanism that would sculpt the contours of the skull according to underlying brain shape

• i.e. there is no correlation between contours of the skull and the underlying size or shape of the brain

• Their psychological ‘model’ was based on common sense constructs of personality

• I.e. Looking in the wrong place for the wrong thing!

But not entirely wrong…

• The idea of functional localisation has survived, but in a different form

• Localisation does not respect character traits, like honesty, peevishness

• Localisation may respect, for example, sensory modality, ‘cognitive systems’ (e.g. LTM), along with other psychological mechanisms yet to be elucidated

Acceptable ‘modern’ principles of functional neuroanatomy

• Functional Segregation• Discrete cognitive functions are localised to

specific parts/circuits of the brain (complex tasks are ‘divided and conquered’)

• Functional Integration• Coordinated interactions between functionally

specialised areas (e.g. during retrieval from episodic memory, reading, perceptual binding etc)

Summary so far

• We want to read a person’s mind from the activity of their brain. E.G. are they lying?

• Their mind is composed of lots of interacting cognitive processes

• Each distinct process is carried out by networks of brain regions, each region is probably performing specific functions, but they all work together

• So we need a device or a technique that can detect changes in brain activity specific to any cognitive process

How to proceed?

• In an experiment we engage different functions in different conditions. For every condition we

• Detect rapid changes in neuronal activity (requires a temporal resolution of milliseconds, 1/100ths of a second)

• Locate activity within brain structures that are engaged (may require an anatomical (spatial) resolution of millimeters or better)

• Currently no such technique exists. Instead we rely on converging data from many techniques

Electrophysiological Techniques

• EEG

• non-invasive recordings from an array of scalp electrodes

EEG Signal Averaging

Averaging EEG produces ERPs

• Portions of the EEG time-locked to an event are averaged together, extracting the neural signature for the ‘event’.

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TIME (sec)0 21

DOG

AIR

SHOE

AVERAGE

What do ERP waveforms tell us?

CONDITION A

CONDITION B

0 1 2

TIME (seconds)

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ONSET OF EVENT

INFORMATION ABOUT THE NEURAL BASIS OF PROCESSING IS PROVIDED BY THE DIFFERENCE IN ACTIVITY

Functional Inferences Based Upon Electrophysiology

• Timing• Upper limit on time it takes

for neural processing to differ• Time course of a process

(onset, duration, offset)• Level at which a process is

engaged• Engagement of multiple

processes at different times or in different conditions

Early Topography

Late Topography

The Brain’s Plumbing

Haemodynamic Techniques

• Oxygen and glucose are supplied by the blood as ‘fuel’ (energy) for the brain

• The brain does not store fuel, so• Blood supply changes as needs arise• Changes are regionally specific - following the local dynamics of neuronal

activity within a region

• Haemodynamic techniques localise brain activity by detecting these regional changes in cerebral blood supply

Positron Emission Tomography (PET)

• Samples the entire brain volume homogeneously

• Has an effective anatomical resolution of about 10mm or so in group studies

• An ‘indirect’ measure of neuronal activity• Due to radiation dose, only a limited

number of scans can be taken from each subject

Magnetic Resonance Imaging (MRI)

• Put head into a strong magnetic field• Water protons align themselves with respect to the field• alignment is then perturbed by radio-frequency pulses• non-invasive and fast (few seconds)• protons ‘relax’ back into alignment, giving off a signal• relaxation signals can reveal

• tissue type• physiological state (e.g. blood oxygenation) • 3D position in the magnetic field

Our starting point …

• Electrophysiological and Haemodynamic techniques• Have different temporal and spatial resolutions• Measure different physiological signals• Constrain experimental design and functional

inferences in different ways• May provide complementary information when

functional maps from each technique can be formally co-registered

ERP PET