35
Meeting Psychofysiologie.be P300 From Practise to Guidelines 28/02/2008 Dr. G. Otte

P300 guidelines

  • Upload
    gotte

  • View
    334

  • Download
    0

Embed Size (px)

Citation preview

Page 1: P300 guidelines

Meeting Psychofysiologie.be

P300 From Practise to Guidelines

28/02/2008

Dr. G. Otte

Page 2: P300 guidelines

Not the P300 again !!!

HELP HELP !!!!!!!!

Page 3: P300 guidelines

The P300

• Born in 1965• 2 fathers: Sutton and Donchin• Off spring >> many 1000 articles and

publications• Star* of the ERP scene because

discrimination of external stimuli is a primary condition in many cognitive activities (attention, memory, action..)

• Evoked by odd-ball paradigma

Page 4: P300 guidelines

What is the meaning of the P300

• Its is only a label for a concept that encompasses the Late positive Complex (LPC) +/-300 msec after a meaningfull stimulus.

Page 5: P300 guidelines

P300 does not exist

• There are two different components– a fronto central P3a (“novelty P3a-NOGO

P3a) dopaminergic-indexes attentional network activation (concept of Posner)

– a temporoparietal P3b indexes memory and context updating and is noradrenergic driven.

Page 6: P300 guidelines
Page 7: P300 guidelines
Page 8: P300 guidelines
Page 9: P300 guidelines
Page 10: P300 guidelines

P3aP3aP3bP3b

FrontalFrontal

DopaminergicDopaminergic

AttentionalAttentional

parietocentralparietocentral

noradrenergicnoradrenergic

Memory Memory encodingencoding

Page 11: P300 guidelines

Guidelines

Use the paradigma that maximises these 2 components

General principle

Page 12: P300 guidelines

Oddball paradigmaOddball paradigma

Page 13: P300 guidelines

Three elements

Page 14: P300 guidelines

Odd ball paradigma

• A rare target stimulus is presented with low probability (15-20%) in a series of frequent standard stimuli (modality independent)

• The patient has a primary task to perform on the target stimulus– Overt: pressing a button– Covert: counting silently the number of targets– Combined

Page 15: P300 guidelines

Odd ball paradigma

• A rare target stimulus is presented with low probability (15-20%) in a series of frequent standard stimuli (modality independent)

• The patient has a primary task to perform on the target stimulus– Overt: pressing a button– Covert: counting silently the number of targets– Combined

Page 16: P300 guidelines

Odd ball paradigma

• A rare target stimulus is presented with low probability (15-20%) in a series of frequent standard stimuli (modality independent)

• The patient has a primary task to perform on the target stimulus– Overt: pressing a button– Covert: counting silently the number of targets– Combination of both

Page 17: P300 guidelines

Type 1: easy discrimination

S:Standard: 1000 Hz

T: Target: 2000 hz

(Classical type)

Page 18: P300 guidelines

The amplitudo of the P300 on the target is inversely related to the probability of its occurence which can be expressed as a local probability : intertarget interval (ITI) N: number of standards between targets

The amplitudo increases on increasing ITI untill ~= around 8.

It fits a sec. order polynomial especially in visual modality where this effect is more pronounced.

Page 19: P300 guidelines

Importance of Intertarget Interval ?A P300 (P3a) can be seen on simple stimuli independent on patient cooperation if the interval between stimuli is long enough (6-8 sec).

Every stimulus is then a target.

Can be very interesting to test P3a in mentally handicapped or other patients who cannot (will not) perform the primary task

Page 20: P300 guidelines

Other factors influence amplitudo and latency

RESOURCERESOURCE ALLOCATIONALLOCATION

Arousal: tonic and phasicArousal: tonic and phasic

Page 21: P300 guidelines

3 way stimulus

Target is difficult to discriminate from standard: attentional resources are allocated: large P3b

Infrequently and irregularely a strange more salient “distractor” stimulus is given (patient should not react on it): this “salient or novel” stimulus generates a large frontocentral P3a.

Page 22: P300 guidelines

Novel

Standard

Target

Page 23: P300 guidelines

Primary task

Examples from the clinic

Page 24: P300 guidelines

Note a low voltage MMN area (adjacent to N1)

Oddball paradigma: 80 % standard 20% “target” easy discrimination (S:1000 Hz / T: 2000 Hz)

No primary task asked to patient

Boils down to MMN

Page 25: P300 guidelines

Primary task:

“OvertOvert” Press RT button and

“covertcovert” count number of rare stimuli:

Result: Low voltage P300-non closure of CN in Cz and Pz

Count: correct

“Classical P300 odd-ball”: combined task

Page 26: P300 guidelines

Task: P300: tap finger (no counting) on rare

stimulus: GO condition

GO conditionGO condition

Very low voltage P3a- delayed P3b and non closure CN

Page 27: P300 guidelines

Task: tap finger on frequent only ( no no tappingtapping on rare: NO-GO).

NO-GO conditionNO-GO condition

Activates a large frontal P3a (“No GO” P3a)

Page 28: P300 guidelines

Let us recapitulate

• Compare 4 different tasks and their influence on “the P300”

Page 29: P300 guidelines

No P300No P300

FIRST: NO TASK at all

No task No attentionNo task No attention

Small preattentive MMN adjacent to N1

Page 30: P300 guidelines

Oddball P300:overt (press RT button)Oddball P300:overt (press RT button) Oddball P300:overt + covert (press Oddball P300:overt + covert (press RT button and cound targets)RT button and cound targets)

<<Larger P300 <<Larger P300 (counting adds (counting adds attentional attentional resources to the resources to the task)task)

Larger P300Larger P300

Counting Counting mobilises more mobilises more

attentional attentional resourcesresources

Page 31: P300 guidelines

NOGO conditionNOGO condition Overt + covertOvert + covert overtovert

No motor involvementNo motor involvement motor involvementmotor involvement

Page 32: P300 guidelines

Influence of motor task

• It activates motor related potentials that cover the same time window as P3

• The medial BP can contaminate the P3

• Some motor potentials are lateralised (LRP) and in right handed people might obscure a lateral assymetry that is often seen in left temporal cortex of schidzophrenic patients.

Page 33: P300 guidelines

Paradigma

• Single target: in patients unable to apply the primary task

• 3 way oddball: in all other patient– Use overt: (motor task) to obtain sequential reaction

times and after that a secund run but– Using covert ( count only-no motor task) to eliminate

contribution of motor related potentials (P3b will be higher)

– Use covert difficult task to appreciate attentional resources (TINNV D. de Batisse-Campanella-M.van de Velde) (but more clinical studies needed)

Page 34: P300 guidelines

3 way paradigma

Page 35: P300 guidelines

Conclusion

• In daily clinical routine a rigid standardised paradigm (fi 3 way) and task procedure is IMPERATIVE in order to lower outcome variance and allow multicentre comparison of results (and building normal databases).

• Freedom of testing is allowed but only in research situations.