Cross-talk between conscious and non conscious mind: Cortical mechanisms and clinical implications...

Cross-talk between conscious and non conscious mind: Cross-talk between conscious and non conscious mind: Cortical mechanisms and clinical implicationsCortical mechanisms and clinical implications

Rajendra D. Badgaiyan, MD

Departments of Psychiatry and Radiology, Harvard Medical SchoolDepartment of Psychology, Harvard University

Massachusetts General Hospital, Boston

‘Normal’ cognitive experience requires:• intact conscious and non conscious processes• balanced information sharing between the two processes

To understand neural basis of cognitive impairments, we need to know • neural network of conscious and non conscious processes• neural network that allows two processes to share information

Cognition

Conscious

Non conscious

Classical concept: • short term memory (STM) • long term memory (LTM)

Stimulus STM LTM (Attkinson & Shiffrin, 1968)

Problems: patients with STM deficits may have normal LTM (Braddley & Hitch, 1974)

amnesics with both STM and LTM deficits show normal performance in a variety of tests of memory (Milner, 1966)

Current concept: (Graf & Schacter, 1985)

explicit: conscious and intentional implicit: non conscious and incidental

Memory: a model for the study of conscious and non conscious processes

Instructions:

explicit: remember words complete word-stems using a studied word

implicit: count vowels complete word-stems using the first word that comes to mind

2. Picture recognition test:

STUDY TESTpictures shown for 3 sec studied and non studied

pictures flashed for 16 msecInstructions:

explicit: remember pictures indicate whether the picture was studied

implicit: look at the pictures indicate if you can recognize the picture

1. Word-stem completion task:

STUDY TESTinstitution pic

picture insfaculty fac

Memory is a good model for the study of neural basis of conscious and non conscious cognitive processes and their interaction:

• it has a conscious and a non conscious component• two components are dissociable in neuropsychiatric disorders

• schizophrenia• depression• parkinsonism

• evidence suggest that the two components interact with each other

Cognition

Conscious

Non conscious

Remember following words:

candy sour sugar bitter goodtaste nice honey soda chocolateheart cake eat fruit pie

Interaction between explicit and implicit processes….Interaction between explicit and implicit processes….

Louis Wain (1860-1939)Louis Wain (1860-1939) The ‘King of cat art’The ‘King of cat art’

TASTE

Did you see following word in the list just studied?

POINT

Did you see following word in the list just studied?

SWEET

Did you see following word in the list just studied?

So, we had three words…..

TASTEPOINTSWEET

Implicit memory (stem-completion task)conscious action finding a word beginning with word stemnonconscious action retrieval of a studied word

conscious action/cognition

non conscious processing

Conscious

Non conscious

Explicit memory (false memory)conscious action encoding and retrieval of studied wordsnonconscious action semantic organization of studied words

‘altered’ non conscious processing ‘altered’ conscious cognition

• false memory delusional disorder• PTSD• hallucination

‘resetting’ of non conscious processing ‘resetting’ of conscious cognition

• cognitive techniques (e.g., Crovitz technique in psychogenic amnesia)• ? Neurophysiological/neurochemical techniques

conscious cognition

non conscious processing

Conscious

Non conscious

conscious behavior/cognition could be altered by impairments of • conscious processing• nonconscious processing• interaction between conscious and nonconscious processing

using neuroimaging methods, we studied• sites of conscious (explicit) memory• sites of nonconscious (implicit) memory• sites of interaction

conscious behavior/cognitionConscious

Non conscious

Event-related potentials (ERP): high-density EEG recording high temporal but poor spatial

resolution

Positron emission tomography (PET): changes in regional cerebral blood flow (rCBF) estimated using radioactive tracer inhalation high spatial but poor temporal

resolution

Functional magnetic resonance imaging (fMRI): changes in rCBF estimated by measuring ratio of oxygenated/ deoxygenated blood

high spatial but poor temporal resolution

Neuroimaging techniques usedNeuroimaging techniques used

Conscious Conscious retrievalretrieval

Studied picturesActivationssup/ mid frontal gyrus (BA 9/46)hippocampus

Deactivationsextrastriate cortex (BA 19)

R

<.001

<.0001

Badgaiyan & Posner, 1998

Conscious RetrievalBaseline

200

Right prefrontal

Conscious retrieval: studied words

500 ms

.001

.01

.05

600

4 µV

-2 µV

Badgaiyan & Posner, 1998

-2µV

2µV

800

Conscious retrieval: studied words

20 0

36 8 ms

.001

.01.05

P<

Extrastriate cortex

Conscious RetrievalBaseline

Conscious retrieval: studied wordsBESA algorithm

a single dipole source located in the right hippocampus wasresponsible for 84 % of activity between 164 - 200 ms

Badgaiyan & Posner, 1997

R

Processing sequence: conscious retrievalProcessing sequence: conscious retrieval extrastriate cortex: 64 - 600 mshippocampus: 164 - 200 msprefrontal cortex: 200 - 600 ms

64

200 164

Implicit retrievalPicture recognition

Deactivationsextrastriate cortex (BA 19)

Badgaiyan, 2000

R

Implicit retrievalWord stem completion

Deactivationsextrastriate cortex (BA 19)

Schacter, Badgaiyan & Alpert, 1999

R

- 2 µ V

2 µ V

2 0 0

Nonconscious retrieval (priming)

800

Baseline

Priming

1 2 0 m s

.001

.01

.05

P<

Badgaiyan & Posner, 1996

Auditory word stem completion task

Study Testlisten: words listen: word-stems (first syllable)

Instruction: complete word-stems using the first word that comes to mind

Auditory priming (implicit retrieval)

to ascertain that the extrastriate involvement is associated with implicit retrieval and not with some aspect of visual perceptual processing

Auditory priming

Experiment 1 Experiment 2

Deactivationsextrastriate cortex (BA 19)

medial prefrontal cortex (BA 9/10)

Badgaiyan, Schacter & Alpert, 1999

RLL

Visual-to-auditory

Study Test see: words listen: word stems (first syllable)

Auditory-to-visual

Study Test listen: words see: word stems (first 3-letters)

Instruction: complete word-stems using the first word that comes to mind

Cross-modality primingCross-modality priming

to understand cortical mechanism of non-perceptual priming, we examined implicit memory under cross-modality priming condition

Cross-modality (visual auditory) priming

Activationsuperior frontal gyrus (BA 9/10)

Badgaiyan, Schacter & Alpert, 1999

RLL

Cross-modality (auditory visual) priming

Activationsuperior frontal gyrus (BA 9/10)

Schacter, Badgaiyan & Alpert, 1999

L

Cortical areas associated with conscious and nonconscious memory

Explicit (conscious) memory

Implicit (nonconscious) memory

extrastriate deactivation during conscious retrieval of studied items

prefrontal activation during non conscious retrieval under cross modality condition

suggest cross-talk….

Neural evidence of interaction between explicit and implicit memoryNeural evidence of interaction between explicit and implicit memory

Reduced activation in the extrastriate cortex (BA 19) during:Reduced activation in the extrastriate cortex (BA 19) during:• implicit retrievalimplicit retrieval• explicit retrieval of studied itemsexplicit retrieval of studied items

Retrieval of studied pictures

Conscious retrieval Non conscious retrieval

R L

-2 µV

2 µV

Nonconscious retrieval

800

Baseline

Nonconscious retrieval

-2µV

2µV

800

Baseline

Conscious retrieval Conscious retrieval

20 0

Time course of extrastriate deactivationTime course of extrastriate deactivation

200

4µV

200 600

Frontal channels

-2µV

Conscious

Nonconscious

Time course of prefrontal and late extrastriate activityTime course of prefrontal and late extrastriate activity

-2µV

2µV

Posterior channels

200 600

Cognitive component retrieval of studied retrieval of studied items items

conscious awareness of retrieval

Late extrastriate deactivation and prefrontal activity associated with conscious awareness ?

Cortical processing of memoryCortical processing of memory

Nonconscious Conscious

Cortical activity extrastriate (early) extrastriate (early) extrastriate (late) prefrontal cortex

Processing sequence: conscious retrievalProcessing sequence: conscious retrieval extrastriate cortex: 64 - 200 ms (early)

extrastriate cortex: 200 - 600 ms (late) hippocampus: 164 - 200 msprefrontal cortex: 200 - 600 ms

• 64-200 ms: implicit retrieval • 200-600 ms: extrastriate cortex

holds implicitly retrieved

information

• re-entrant circuit sets up between extrastriate and Prefrontal cortex

• conscious awareness

64

200 164

Neuropsychiatric conditions associated withNeuropsychiatric conditions associated withimpaired explicit but preserved implicit memoryimpaired explicit but preserved implicit memory

• schizophrenia (implicit ‘better than normal’)

• severe PTSD• MPD/psychogenic amnesia

(fugue state)• amnesia (hippocampal lesion)• post-ECT• Alzheimer’s disease • organic depression• anesthetic recovery

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200 164

tests of implicit memory could be useful diagnosis aids for these conditions

Cognitive impairments associated with ‘altered’ signal transmissionCognitive impairments associated with ‘altered’ signal transmission

Increased activity of…

extrastriate -prefrontal connectivity: hallucination

64

200 164 hippocampal -prefrontal connectivity: loose association

Cognitive impairments associated with ‘altered’ signal Cognitive impairments associated with ‘altered’ signal transmissiontransmission

Decreased activity of … extrastriate -prefrontal connectivity: negative symptoms

dementia

delirium

hemineglect

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200 164

Future prospects...Future prospects...

• if the physiological nature of the communication between implicit and explicit processes is known, it can be manipulated to ‘reset’ the impaired communication which can theoretically alleviate cognitive symptoms

• tests of implicit memory may help objective diagnosis of conditions like, PTSD, MPD

• functional neuroimaging studies may help definitive diagnosis of a variety of neuropsychiatric conditions

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200 164

until then, psychiatric conditions will continue to have low inter rater reliability ...

Thank you...