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 persons 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
Averaging EEG produces ERPs Portions of the EEG time-locked to an event are averaged together, extracting the neural signature for the event. 10uV + - TIME (sec) 021 DOG AIR SHOE AVERAGE
What do ERP waveforms tell us? CONDITION A CONDITION B 012 TIME (seconds) 5uV + - 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
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