cross-talk between conscious and non conscious mind: cortical mechanisms and clinical implications...
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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
64
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
64
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
64
200 164
until then, psychiatric conditions will continue to have low inter rater reliability ...
Thank you...