MondayCognitive Electrophysiology
WednesdayPupillometry
MRes Psychophysiology
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 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)
Where We At?
• We want to read a person’s 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
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)0 21
DOG
AIR
SHOE
AVERAGE
What do ERP waveforms tell us?
CONDITION A
CONDITION B
0 1 2
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
Electrophysiological Techniques
Principle advantages non-invasive high temporal resolution direct reflection of neuronal activity easy to produce event-related potentials by
selective averaging of EEG epochs. topographic mapping Cheap (for EEG but not MEG)
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
Stimuli
Time 0.1 0.2 0.40.3 0.5 0.70 0.6
Ecphory?
Monitoring?
Implicit Memory?
Familiarity?
cueonset
Ecphory/inhibition
MonitoringRetrieval Perception/attention
Patterncompletion/
Binding
‘selective attention’
Stimuli
Time 0.1 0.2 0.40.3 0.5 0.70 0.6
CMF{retrieval}
Can We Deliberately Forget?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 The Ullsperger et alet al DF Experiment DF Experiment
0Time -
R or F CueEncoding WILD
2.5s 5.0s
The Ullsperger et al Depth of Processing Experiment
0Time -
D or S CueEncoding WILD
2.5s 5.0s
Ullsperger’s 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 ++ ++
0Time - 1 3 4 65 7 92 8
120 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!
32-ch Montage
CZ
C1
C2
C3C4
C5
S1S2
S3
S4
S5S6
S7
S8
S9
S10 M1
M2
M3
M4M5
M6
M7
M8 I1
I3I4
I5
I6
6 uV
RememberForget
ERP ‘Associates’ of Differential Encoding
ERP Associates of Differential Encoding
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?
Recognition Performance
-20
0
20
40
60
80
100
FORGET MALE 58.57 73.09 75.96 81.9 23.33 16.9
FORGET FEMALE 73.96 57.5 81.66 82.91 17.91 15.4
DF EFFECT 15.39 15.59 5.7 -1.01 -5.42 1.5
MALE HIT
FEM HIT
MALE CR
FEM CR
MALE FA
FEM FA
‘TBRemembered ’ Old/New Effect
CZ
C1
C2
C3C4
C5
S1
S2
S3
S4
S5S6
S7
S8
S9
S10 M1
M2
M3
M4M5
M6
M7
M8 I1
I2
I3I4
I5
I6
6 uV
HITCR
‘TBforgotten’ Old/New Effect
CZ
C1
C2
C3C4
C5
S1
S2
S3
S4
S5S6
S7
S8
S9
S10 M1
M2
M3
M4M5
M6
M7
M8 I1
I2
I3I4
I5
I6
6 uV
HITCR
‘Strong’ Right Frontal Effectfor 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
ForgottenCR
I4
CZ
C1
C2
C3C4
C5
S1
S2
S3
S4
S5S6
S7
S8
S9
S10 M1
M2
M3
M4M5
M6
M7
M8 I1
I3I5
I6
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?