Presentation on theme: "Maps of the Mind Memory and Cognition Lecture 9"— Presentation transcript:
1Maps of the Mind Memory and Cognition Lecture 9 Recognise this? A realistic map of something that does not physically exist, Tolkien’s middle earth. Something to bear in mind for today, a realistic looking map doesn’t necessarily depict reality.Maps of the Mind Memory and Cognition Lecture 9
2Cognitive Neuroscience Methods… ElectrophysiologicalHaemodynamicof seeing inside the box of tricks…
3Psychophysiology Aim is to develop mind reading technologies We are most interested in the PPY of Perception and Cognition. In other words, Cognitive NeuroscienceCan we tell what a person is thinking or experiencing just by looking at their brain activity?
5Phrenology Was Odd…There is no known mechanism that would sculpt the contours of the skull according to underlying brain shapei.e. there is no correlation between local contours of the skull and the underlying size or shape of the brainTheir psychological ‘model’ was based on common sense constructs of personalityI.e. Looking in the wrong place for the wrong thing!
6But not entirely wrong… The idea of functional localisation has survived, but in a different formLocalisation does not respect character traits, like honesty, peevishnessLocalisation may respect, for example, sensory modality, ‘cognitive systems’ (e.g. LTM), along with other psychological mechanisms yet to be elucidated
7Acceptable ‘modern’ principles of functional neuroanatomy Functional SegregationDiscrete cognitive functions are localised to specific parts/circuits of the brain (complex tasks are ‘divided and conquered’)Functional IntegrationCoordinated interactions between functionally specialised areas (e.g. during retrieval from episodic memory, reading, perceptual binding etc)
8Where We At?We want to read a person’s mind from the activity of their brainTheir mind is composed of lots of interacting cognitive processesEach distinct process is carried out by networks of brain regions, each region is probably performing specific functions, but they all work togetherSo we need a device or a technique that can detect changes in brain activity specific to any cognitive process
9So What Do We Need?In an experiment we (think we) engage different functions in different conditions. For every condition weDetect 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
10Electrophysiological Techniques EEGnon-invasive recordings from an array of scalp electrodes
12Averaging EEG produces ERPs DOG10uV+-TIME (sec)21Portions of the EEG time-locked to an event are averaged together, extracting the neural signature for the ‘event’.SHOEAIRHere you can see several individual traces of EEG, associated with a specific class of events, such as the subject reading a series of words.Although there is no specific pattern of brain activity visible in the individual traces, the process of averaging the traces together allows you to see any activity that is consistently present in the resulting ERP for AN EVENT OF THAT TYPEIn contrast any random activity that isn’t associated with the event, such as background activity, will be averaged out.Okay, thats how you get an ERP, but what does this tell you about the neural basis for processing?AVERAGE
13What do ERP waveforms tell us? CONDITION A+5uV-CONDITION BINFORMATION ABOUT THE NEURAL BASIS OF PROCESSING IS PROVIDED BY THE DIFFERENCE IN ACTIVITYONSET OF EVENTWhat kind of information do ERPs provide?Well, here you can see two hypothetical ERPs recorded from 1 scalp electrodeThe y axis shows change in voltage. The x axis shows time, with 0 being the point at which each event begins.As you can see, the voltage changes over the time course of the recording, but the waveforms for the 2 conditions only differ in voltage from about half a second after the onset of the event. At around this time the ERP for condition ‘A’ becomes more positive going.This DIFFERENCE in brain activity reflects the difference in processing between the two conditionsWhat this should make clear is that ERPs provide a high level of temporal resolution about processing, as brain activity is measured every few milliseconds. This level of temporal information about the time course of processing, is simply not provided by other neuroimaging techniques.Secondly, if you imagine that the ERPs are recorded from electrodes all over the scalp, it should be clear that ERPs also provide information about the scalp distribution of any differences in brain activity - something I’ll show you later.12TIME (seconds)
14Functional Inferences Based Upon Electrophysiology Early TopographyTimingUpper limit on time it takes for neural processing to differTime course of a process (onset, duration, offset)Level at which a process is engagedEngagement of multiple processes at different times or in different conditionsLate Topography