Cognitive Neuroscience of Memory

Transcription

1 Cognitive Neuroscience of Memory Types and Structure of Memory Types of Memory Type of Memory Time Course Capacity Conscious Awareness Mechanism of Loss Sensory Short-Term and Working Long-Term Nondeclarative Long-Term Declarative Milliseconds to seconds Seconds to minutes High No Primarily decay Limited Yes Primarily decay Days o years High No Primarily interference Days to years High Yes Primarily interference Types and Structure of Memory Structure of Memory 1

2 Types and Structure of Memory Processes of Memory Encoding Acquisition is the forming of memory traces Consolidation is changing the traces into something stable Storage Retrieval Anatomy of Memory Hippocampus Fornix Entorhinal cortex Perirhinal cortex Prefrontal cortex (MPFC, DLPFC VLPFC, APFC) Anatomy of Memory Amnesiacan tell a lot about memory systems, mechanisms, processes, and memory localization in the cortex Anterograde amnesia Retrograde amnesia Temporally limited Temporal gradient and Ribot s law Surgery and memory loss Extent of removal of posterior medial temporal Lobe is related to severity of amnesia Henny Molaison (HM) 2

3 Anatomy of Memory Digit Spans(STM) vs. Long Term Memories for Digits Amnesiacs show similar digit spans Deficit is in digit spans requiring new Long term memoies Atkinson-Shiffrin (1968) Modal Model of memory Rehearsal Decay Interference Sensory Memory is shortest form of memory Residual traces of sensory information Iconic memory Echoic memory Studying the duration of sensory memory Mismatch Negativity (MMN) in ERPs Mismatch Field (MMF)in fmri These traces last for a short time 3

4 Short Term Memory Limited in capacity (7 +/-2 items) Gateway to LTM? Patient KF Left perisylvian cortex damage STM deficit (digit span) LTM normal (associate learning) Patient EE Left angular gyrus tumor Below normal verbal STM Preserved LTM Working Memory Retaining short term memory (maintenance) through mental operations (manipulations) Central executive Phonological loop Visuospatial sketchpad STM deficits correlate with damage to WM components Lesions to Brodmann 40 & 44 phonological deficits Parieto-occipital region damage Visuospatial deficits Different Anatomical Regions for Working Memory Components Smith et al. (1996) PET study Spatial location probe test Letter probe test 4

5 Location of Spatial Working Memory Spatial WM Task Perceptual Matching Task Activations Extrastriate cortex Posterior parietal cortex Premotor area Spatial Working Memory Corresponds to Dorsal Stream Types of Long Term memory Declarative memory Episodic memory is about for personal events and the context for that information Sematic memory is general, objective knowledge for facts; independent of context Non-declarative memory Implicitly acquired information, with no conscious awareness Priming, conditioning, habituation Procedural memory Depends on repeated experience Learning of motor skills 5

6 Test of Procedural Memory Serial RT Task Press key of corresponding light Part of sequence is repeated No conscious memory RTs decrease for repeated portion Amnesiacs also improve in this task, but without memory of task! Priming Change in responding following exposure to a stimulus Perceptual Representation System (PRS) Word-fragment completion task Does not require conscious encoding Amnesiacs also show priming Memory Formation Seems to Depend on Portions of the Medial Temporal (MT) Lobe For declarative memory formation Episodic memory Semantic memory Non-declarative memory outside MT 6

7 Evidence from HM and amnesia? Not all of HMs hippocampi were removed Patient RB Anterograde amnesia onset following ischemic episode Histological analysis revealed lesion to CA1 pyramidal cells Hippocampus critical to forming new LTM Is hippocampus also involved with memory retrieval? Subsequent Memory Paradigm Present to-be-remembered items (e.g., words) Cortical activity measured with ERP or fmri Memory is assessed for the items Cortical activity during encoding is analyzed conditional on whether studied items were later correctly remembered 7

8 Ranganath et al. (2003) Animacy or size judgments during encoding fmri scans during encoding/rating phase Ranganath et al. (2003) Post-scan memory test Mix of old and new words Rate confidence each word was old or new Also, was word red or green (source memory) Sorted words based on: Correctly recalled or not Correct source identification Ranganath et al. (2003) Examined correct recollection Encoding of later recollected words: Increased hippocampus activation Increased posterior hippocampal complex activation Hippocampus important for encoding 8

9 Retrieval and the Hippocampus? Endridge et al. (2000) Simple study-recognize memory task fmri scans during recognition Correct recollection (recognize + source) increased hemodynamic activity Recollection, Familiarity and MT Lobe Hippocampal complex active for recollection, not familiarity What regions are involved with episodic vs. non-episodic memory? What an item is Perirhinalcortex (PRC) Where something is located parahippocampal cortex (PHC) Relational memory PHC and PRC converge in hippocampus Binding of contextual (episodic) and item memory Increased activation in rhinal cortex as studied item familiarity increases Ranganath et al. (2003) This is for the encoding of information 9

10 What About Retrieval? Montaldi et al. (2006) Study-recognize task fmri scans during retrieval Hippocampus active for recollected items only Perirhinal cortex active based on strength of familiarity What about False Memories? Study list of related words (thread, pin, pain, eye, sewing, sharp, point, haystack) People falsely recognize studying a highly related item (needle) True and False recognition show similar bilateral hippocampal activity False recognition differs from True recognition activity in PHG Image References 10