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’.

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What do ERP waveforms tell us?

CONDITION A

CONDITION B

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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

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

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R or F CueEncoding WILD

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The Ullsperger et al Depth of Processing Experiment

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D or S CueEncoding WILD

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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!

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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

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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

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‘TBRemembered ’ Old/New Effect

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‘TBforgotten’ Old/New Effect

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‘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

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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?