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Cross-talk between conscious and non conscious mind: Cortical mechanisms and clinical implications Rajendra D. Badgaiyan, MD Departments of Psychiatry and Radiology, Harvard Medical School Department of Psychology, Harvard University Massachusetts General Hospital, Boston.
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Cross-talk between conscious and non conscious mind: Cortical mechanisms and clinical implications Rajendra D. Badgaiyan, MD Departments of Psychiatry and Radiology, Harvard Medical School Department 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
Memory: a model for the study of conscious and non conscious processes • 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
1. Word-stem completion task: STUDY TEST institution pic picture ins faculty fac 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 TEST pictures shown for 3 sec studied and non studied pictures flashed for 16 msec Instructions: explicit: remember picturesindicate whether the picture was studied implicit: look at the pictures indicate if you can recognize the picture
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
Interaction between explicit and implicit processes…. Remember following words: candy sour sugar bitter good taste nice honey soda chocolate heart cake eat fruit pie
Louis Wain (1860-1939) The ‘King of cat art’
So, we had three words….. TASTE POINT SWEET
Explicit memory (false memory) conscious action encoding and retrieval of studied words nonconscious action semantic organization of studied words Implicit memory (stem-completion task) conscious action finding a word beginning with word stem nonconscious action retrieval of a studied word conscious action/cognition non conscious processing
conscious cognition non conscious processing • ‘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 behavior/cognition • 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
Neuroimaging techniques used 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
Conscious retrieval Studied pictures Activations sup/ mid frontal gyrus (BA 9/46) hippocampus Deactivations extrastriate cortex (BA 19) R
Conscious retrieval: studied words BESA algorithm a single dipole source located in the right hippocampus was responsible for 84 % of activity between 164 - 200 ms Badgaiyan & Posner, 1997
Processing sequence: conscious retrievalextrastriate cortex: 64 - 600 ms hippocampus: 164 - 200 ms prefrontal cortex: 200 - 600 ms
Implicit retrievalPicture recognition Deactivations extrastriate cortex (BA 19) Badgaiyan, 2000
Implicit retrievalWord stem completion Deactivations extrastriate cortex (BA 19) Schacter, Badgaiyan & Alpert, 1999
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 word stem completion task Study Test listen: words listen: word-stems (first syllable) Instruction: complete word-stems using the first word that comes to mind
Auditory priming Deactivations extrastriate cortex (BA 19) medial prefrontal cortex (BA 9/10) Experiment 1 Experiment 2 Badgaiyan, Schacter & Alpert, 1999
Cross-modality priming to understand cortical mechanism of non-perceptual priming, we examined implicit memory under cross-modality priming condition 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 (visual auditory) priming Activation superior frontal gyrus (BA 9/10) Badgaiyan, Schacter & Alpert, 1999
Cross-modality (auditory visual) priming Activation superior frontal gyrus (BA 9/10) Schacter, Badgaiyan & Alpert, 1999
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 memory • Reduced activation in the extrastriate cortex (BA 19) during: • implicit retrieval • explicit retrieval of studied items Retrieval of studied pictures Conscious retrieval Non conscious retrieval
Time course of extrastriate deactivation Nonconscious retrieval Nonconscious retrieval Baseline 2 µ V 200 800 - 2 µ V
Cortical processing of memory Nonconscious Conscious Cortical activity extrastriate (early) extrastriate (early) extrastriate (late) prefrontal cortex Cognitive component retrieval of studied retrieval of studied items items conscious awareness of retrieval Late extrastriate deactivation and prefrontal activity associated with conscious awareness ?
Processing sequence: conscious retrievalextrastriate cortex: 64 - 200 ms (early) extrastriate cortex: 200 - 600 ms (late) hippocampus: 164 - 200 ms prefrontal 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
Neuropsychiatric conditions associated withimpaired 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 tests of implicit memory could be useful diagnosis aids for these conditions
Cognitive impairments associated with ‘altered’ signal transmission Increased activity of… extrastriate -prefrontal connectivity: hallucination hippocampal -prefrontal connectivity: loose association
Cognitive impairments associated with ‘altered’ signal transmission Decreased activity of … extrastriate -prefrontal connectivity: negative symptoms dementia delirium hemineglect
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 until then, psychiatric conditions will continue to have low inter rater reliability ...