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?
Acceptable modern principles of functional neuroanatomy Functional Segregation l Discrete cognitive functions are localised to specific parts/circuits of the brain (complex tasks are divided and conquered) Functional Integration l Coordinated interactions between functionally specialised areas (e.g. during retrieval from episodic memory, reading, perceptual binding etc)
Where We At? We want to read a persons mind from the activity of their brain 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
So What Do We Need? In an experiment we (think 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
S Electrophysiological Techniques SEEG S 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 STiming SUpper limit on time it takes for neural processing to differ STime course of a process (onset, duration, offset) SLevel at which a process is engaged SEngagement of multiple processes at different times or in different conditions Early Topography Late Topography
S Electrophysiological Techniques SPrinciple advantages Snon-invasive Shigh temporal resolution Sdirect reflection of neuronal activity Seasy to produce event-related potentials by selective averaging of EEG epochs. Stopographic mapping SCheap (for EEG but not MEG)
Our starting point … Electrophysiological and Haemodynamic techniques l Have different temporal and spatial resolutions l Measure different physiological signals l Constrain experimental design and functional inferences in different ways l May provide complementary information when functional maps from each technique can be formally co-registered ERP PET
Stimuli Time Ecphory? Monitoring? Implicit Memory? Familiarity?
Can We Deliberately Forget? What functional changes in memory produce deliberate forgetting? Encoding:differential rehearsal / encoding of TBR items (likened to a dop manipulation) Retrieval:Selective inhibition of TBF items
The Ullsperger et al DF Experiment 0 Time - R or F Cue Encoding WILD 2.5s5.0s
The Ullsperger et al Depth of Processing Experiment 0 Time - D or S Cue Encoding WILD 2.5s5.0s
Ullspergers Conclusion Differential encoding hypothesis does not account for the DF and DOP findings:- The enhanced RF effect does not appear to be a response to the mere difficulty in remembering TBF items. Can ERPs be used to explore mechanisms that overcome retrieval inhibition? With consequences for our understanding of normal memory function, cognitive aging, functional amnesias and affective disorders with strong memory components (e.g. P.T.S.D.)?
Face DF Experiment Methods Stimuli ++ 0 Time study items, 60 male / 60 female. 240 test items, 120 male / 120 female. Encoding and Retrieval phase trial structure were identical. EEG was recorded continuously throughout encoding and retrieval.
Why We Did It Like We Did 1.ERPs from the study phase may reveal, directly, neural correlates of differential encoding of TBR and TBF items. 2.Hence, these may contrasted, directly, with neural correlates of retrieval processing for TBR and TBF items. 3.Processing of cues belonging to the TBF and TBR classes may differ in a way that is functionally related to forgetting. 4.What is the fate of genuinely forgotten items? 5.A change is as good as a rest!
Have not been reported, yet, in the literature (I think!) Are sustained, onsetting around 400ms, still present at ~2s post-stimulus. Change topographically over time, indicating engagement of multiple regions/functions. Ironically, they differ from associates of DOP effects at encoding! Bear a family resemblance to old/new effects… What about the test phase performance and ERP data?
TBRemembered Old/New Effect 6 uV HIT CR
TBforgotten Old/New Effect 6 uV HIT CR
Strong Right Frontal Effect for Remember-Items
Relative-Absence of Right Frontal Effect for Forget-Items
Effects of DF on ERPs at Retrieval 1. The functional state of the brain captured by old/new effects is different when remembering TBF and TBR items, though not in a way that reveals the operation of retrieval inhibition. DF eliminates (effectively) the right frontal component of the old/new effect and the earlier left parietal component too. 2. So contrary to Ullsperger et al, no evidence here for a link between the right frontal effect and the overcoming of retrieval inhibition. But what is the fate of items that are forgotten – i.e. items that are truly inhibited?
A True Associate of Retrieval Inhibition? 6 uV Forgotten CR I4
ERP Associates of Forgetting 1. Resemble the early left parietal component of the old/new effects! Did the subjects disregard weaker memory, or have we detected a lie? 2. Resemble an inverted right frontal effect! Are items forgotten when the RF generators are particularly inactive (i.e. below the correct rejection baseline)? Perhaps they are not responding to the weak memory output reflected by the LP effect?)
Conclusions from Electrophysiological Findings 1. We may be able to use the ERP encoding effects to explore differential encoding as it relates to subsequent forgetting. 2. Contrary to Ullsperger, Inhibition can be overcome without the help of enhanced processing reflected by big RF effects. 3. However, we found that inversion of the RF effect accompanies genuine forgetting. Can we both be right?