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Overview PSY393 Cognitive Neuroscience Memory • Introduction • H.M. • Short-term memory • Sensory memory • Short-term memory store Donna Rose Addis 13 Nov 2003 • Long-term memory • The model of long term memory • Neuroanatomy of long term memory Introduction H.M.: Who is he? • The most famous case of amnesia • What is learning and memory • Learning = acquisition • Memory = persistence of learning • Stages of learning and memory • Encoding – study phase • Storage – retention interval • Retrieval – test phase • Case details: • • • • Absence seizures started at 10 yrs old Generalized seizures started at 16 Medication were not controlling seizures At 27 yrs: Surgery to remove his medial temporal lobe bilaterally H.M.: Areas of brain damage • Removal of bilateral medial temporal lobe H.M.: Areas of brain damage • Removal of bilateral medial temporal lobe Hippocampus (1) Hippocampus (1) Parahippocampal gyrus (2) Parahippocampal gyrus (2) 1 H.M.: Areas of brain damage • Removal of bilateral medial temporal lobe H.M.: Who is he? • Result of this surgery: Global amnesia • Anterograde amnesia: - unable to form new long-term memories • Retrograde amnesia: - unable to retrieve any memories from the 11 yrs before his surgery - Because of his seizures? • BUT other aspects of memory are preserved, Hippocampus & parahippocampal gyrus removed • e.g., short term memory • Dissociation indicates separate memory systems Short-term memory MEMORY Short-term memory STM: Sensory Memory • Very short duration (seconds) Long-term memory • Decays rapidly – tested by partial report • Capacity: ~ 12 items Sensory memory Iconic memory Echoic memory Short-term / working memory Visuospatial sketchpad • Echoic memory: - Sensory memory for auditory information (echo) Phonological Loop Central Executive • Iconic memory: - Sensory memory for visual information (afterimage) STM: STM store • Short-term Memory • Duration: seconds to minutes STM: STM store • Ways of testing short-term memory - Visual memory: Rey Complex Figure COPY • Capacity: Magic number 7 ± 2 chunks • Ways of testing short-term memory - Visual memory: geometric figures that are difficult to verbalize 2 STM: STM store STM: STM store • Ways of testing short-term memory - Visual memory: Rey Complex Figure RECALL • Ways of testing short-term memory - Verbal memory: stories, word pairs, word lists • Serial position effect: - Primacy vs. Recency effects Primacy STM: Serial Position effect Recency STM: Modal model • Primacy effect • (Atkinson & Shiffrin, 1968) - more rehearsal, enters LTM - Faster presentation rate = Ð primacy • Recency effect - Info still in STM, so dumped out - Distractor at end of list = Ð recency Sensory Inputs Sensory memory ATTENTION Primacy Recency Short-term storage REHEARSAL Long-term storage STM: Levels of Processing • (Craik and Lockhart, 1972) • Effectiveness of different encoding strategies • Deeper encoding more effective - e.g., Is it living? - Elaborative – relate info to previous knowledge • Shallow encoding not as effective - (e.g., font size) - Processing only surface features • Not consistent with modal model • Getting info into LTM not just about how long you hold it in STM, but how you process it STM: Lesion evidence • Patient H.M.: Spared STM, Impaired LTM • Can repeat and remember 5 digits as long as he isn’t distracted from rehearsing • BUT this information doesn’t get into LTM • Described as “marooned in the moment” • Patient E.E.: Impaired STM, Spared LTM • Tumour in inferior parietal/superior temporal cortex • Impaired STM, preserved LTM Double Dissociation 3 Long-term memory: Explicit Memory • Episodic memory (Tulving, 1972) MEMORY Short-term memory Long-term memory Explicit memory (Declarative memory) Episodic Semantic (events) (facts) • Specific personal experiences from particular time & place LTM: Explicit Memory - Personally experienced events - Specific time and place – context - Conscious awareness that it is our personal past, we remember that we did that, we can recollect details about the context - e.g., remembering when you first held your baby sister • General Knowledge LTM: Explicit Memory • Semantic memory (Tulving, 1972) - Facts we know about the world - Lacks contextual information - Even if we remember the episode we acquired the fact, the fact itself is distinct - e.g., knowing that Mr. Tim Hortons was a hockey player for the Leafs LTM: Explicit Memory • Semantic Dementia - Damage to the anterior inferior temporal cortex - Impaired semantic memory: Impaired at naming objects, can’t tell you about famous people or events - Spared episodic memory • Consider these patients and K.C.: Double Dissociation LTM: Explicit Memory • Patient K.C. (Rosenbaum et al., 2000) - Damage to his hippocampus bilaterally (motorbike accident) - Spared semantic memory, e.g., defining words - Spared personal semantic memory, e.g., names of work friends - Impaired episodic memory: e.g., cannot recall any specific episodes at work or with those friends LTM: Testing Explicit Memory • Recall versus Recognition - Recall: e.g., tell me what words were on the list - If a patient can’t recall a memory, it could mean either they just can’t retrieve it, or there is no memory there to retrieve - Recognition: e.g., was DEFINE on the list? Y/N - We are providing direct cues to the information - Even if their retrieval processes are not working effectively, if the information is there, they will be able to recognize it 4 LTM: Testing Explicit Memory LTM: Testing Explicit Memory • The Remember-Know paradigm • The Remember-Know paradigm: Patient Jon - Can test whether someone has an episodic or semantic memory of some information - “I remember when ….” vs. “I know that ……” - E.g., a famous name such as “Princess Diana” or “Margaret Thatcher” - Answer Remember if you can actually remember a personal episode connected to her - Answer Know if you know who this person is, but can’t remember a specific episode LTM: Testing Explicit Memory - Hippocampal damage as a baby Some personal events he could remember Some he was only knew about Greater activation of his residual hippocampus when retrieving “remembered” events versus “known” events LTM: Testing Explicit Memory • Verbal and Visual memory - Verbal memory: word-pairs and stories after a delay - Visual memory: Rey complex figure after delay TRY IT!! • Verbal & visual memory (encoding & retrieval) - Verbal memory: supported by the left MTL - Visual memory: supported by the right MTL - e.g., temporal lobe epilepsy patients with damage to : - Left medial temporal lobe = difficulties mainly with verbal memory - Right medial temporal lobe = difficulties mainly with visual memory Double Dissociation LTM: Explicit Memory LTM: Explicit Memory • Anterograde memory • Anterograde memory - Memory for information since the brain injury - Represents ability to form new LTMs • Retrograde memory • Retrograde memory - Memory for information presented before the brain injury - Represents ability to retrieve older LTMs - Temporally graded or flat gradient Retrograde Amnesia INJURY temporal gradient - Memory for information since the brain injury - Represents ability to form new LTMs Anterograde Amnesia - Memory for information presented before the brain injury - Represents ability to retrieve older LTMs - Temporally graded or flat gradient Retrograde Amnesia time flat gradient INJURY Anterograde Amnesia time 5 LTM: Explicit Memory Long-term memory: Implicit Memory • Often get some degree of both, e.g., H.M. • Why? Depend to some extent on the same brain structures (e.g., hippocampus) • Patient M.L.: Isolated retrograde amnesia - Severe retrograde amnesia - Initially had anterograde amnesia but this resolved quickly MEMORY Short-term memory Long-term memory Explicit memory Implicit memory (declarative memory) (non-declarative memory) Procedural Memory Perceptual Representation System Classical Conditioning Non-associative learning Dissociation LTM: Implicit Memory LTM: Implicit Memory • Implicit memory typically outside of awareness • Procedural memory - Learning skills; e.g., riding a bike, mirror-drawing 2nd day 3rd day Number of errors 1st day • Perceptual priming - Being primed to use certain information - Shown a list of words such as DEFINE - Later given stems and asked to complete it with the first word that comes to mind: - e.g., DEF Î Most likely to give DEFINE even if you can’t explicitly remember that word being on the list Attempts each day LTM: Implicit Memory LTM: Implicit Memory • Is implicit memory impaired in amnesia? • Classical conditioning - Pavlovian conditioning - conditioned stimulus paired with an unconditioned stimulus • Non-associative learning - e.g., habituation or sensitization - Often when explicit memory is impaired, implicit memory remains intact • Patient H.M.: Mirror drawing - Got faster each time, made less errors - Indicates he was “learning” this task - BUT each time, he had no explicit memory that he had ever seen this task before • Patient H.M.: Priming - Completed word stems with words from the list even though he had no explicit memory for them being on the list 6 LTM: Implicit Memory • Are there patients showing the opposite? • Patient M.S.: Priming - Damage to the right occipital lobe - Impaired on priming tasks, but spared explicit memory • Parkinson’s disease: Procedural memory - Damage to the basal ganglia - Impaired on skill learning; also habituation LTM: Neuroanatomy • What regions of the brain support LTM? • What role do they play? • What’s the evidence? • Lesion cases • Neuroimaging Double Dissociation LTM: Role of the medial temporal lobes • Medial temporal lobes - H.M. was the first case to highlight the importance of the MTL in forming new memories and retrieving old memories - Anterograde amnesia - Retrograde amnesia (temporal gradient) So, the MTL is important in LTM … ... But what does it do? LTM: Role of the medial temporal lobes • Medial temporal lobes and encoding: - Forms links between information (Eichenbaum, 1991) - e.g., between items (banana – dog) - e.g., between an item and its context (the word DEFINE was in list 2) - Detects novel stimuli (Tulving et al., 1994) - Activates more when encoding information we haven’t seen before - Continuously records experience (Moscovitch, 1992) LTM: Role of the medial temporal lobes • fMRI: MTL is active during successful encoding Wagner et al., 1998 LTM: Role of the medial temporal lobes • What is the role of the MTL in LTM? 1. Consolidation hypothesis (Squire) - When just encoded, memories are dependent on the hippocampus for retrieval - After a while, they become “consolidated”, i.e., independent of the MTL, dependent on the cortex - Explains temporal gradients: information not yet consolidated cannot be retrieved once hippocampus is damaged Retrograde Amnesia INJURY Anterograde Amnesia 7 LTM: Role of the medial temporal lobes • What is the role of the MTL in LTM? LTM: Role of the medial temporal lobes • fMRI: Retrieving details of episodic memories 1. Consolidation hypothesis 2. Multiple Trace Theory (Nadel and Moscovitch, 1997) - Hippocampus important in retrieval of ALL truly episodic memories - Explains flat retrograde amnesia - What about temporal gradients? - Older episodic memories often become semantic and so don’t need the hippocampus for retrieval - The hippocampus is an integrator of context and recollective details of episodic memories When we retrieve memories with more details, the hippocampus is more active R Addis et al. (in press) LTM: Role of the Prefrontal Cortex • MTL not the only region involved in LTM • Prefrontal cortex also play important role • Summarized in the HERA model (Cabeza et al) - LTM: Role of the Prefrontal Cortex • Encoding: Left Prefrontal Cortex - Hemispheric Encoding/Retrieval Asymmetry - LTM: Role of the Prefrontal Cortex • Retrieval: Right Prefrontal Cortex - Important in processing supporting retrieval - e.g., strategies used to search for a memory - Post-retrieval processing, e.g., verification - Right PFC damage: Confabulation (“honest lying”) - Often produce “memories” that are actually composites of different real events and aspects of semantic memory - WHY? - Compensation for lack of episodic detail - Lack of verification - Inability to inhibit responses Supports the use of encoding strategies Impaired frontal functioning: e.g., older adults: - Tend to use shallow encoding strategies - Show poorer performance on encoding tasks Successful encoding shows greater activation of left PFC (Wagner et al., 1998) LTM: Role of the Diencephalon • Damage to regions such as dorsomedial thalamus and mammillary bodies causes amnesia - Similar to MTL amnesia - Impaired explicit / spared implicit memory • Causes of damage: - Alcoholism and thiamine deficiency: Korsakoff’s syndrome - Strokes - Fencing foils (case N.A.) and snooker cues (case B.J.) entering the brain via the nostril 8 LTM: Role of the Diencephalon • Summary: Important memory dissociations What role does the diencephalon play? (Hodges and McCarthy, 1993) • Short-term vs. long-term memory - • Explicit vs. implicit memory - Case P.S.: Stroke in DM thalamus Severe retrograde amnesia Link between frontal lobes (search strategies) and posterior neocortex (stored memory traces) Damage = disconnection syndrome Can’t use search strategies to search through memory traces • Semantic vs. episodic memory • Anterograde vs. retrograde memory • Verbal vs. non-verbal memory 9