Neural Bases of Memory Systems PDF 2018

On The Neural Bases of The Memory Systems Venu Balasubramanian, Ph.D, CCC-S Dept. of Speech-Language Pathology SMHS, Seton Hall University South Orange, NJ USA Introduction: Memory Systems Memory implies a tempora...

On The Neural Bases of The Memory Systems Venu Balasubramanian, Ph.D, CCC-S Dept. of Speech-Language Pathology SMHS, Seton Hall University South Orange, NJ USA Introduction: Memory Systems Memory implies a temporal component: We remember things over time – short periods & long periods (Gazzaniga, Ivry & Mangun, 2009). “Mental time travel” (Endel Tulving): The act of remembering something that happened in the past is to re-experience that past in the present. Hence, contemporary models of memory include the distinctions among Sensory memory: has lifetime measurable in milliseconds to seconds Introduction: Memory Systems (continued) Long-term memory: measured in days or years Early research on memory: Lashley1920 s mass action principle, & concept of engrams On the contrary, subsequent single case studies of brain damaged patients have led to the formulation of models (classification) of memory systems Memory at the Brain Systems Level Karl Lashley : -memory traces (engrams) are found throughout the brain -no single brain region has a privileged role in memory Contrary to those ideas, a number of case reports seem to suggest -different brain regions play different or special roles in different kinds of memory & different stages of processing The medial temporal lobes (MTL) are critically important in encoding and consolidating the sorts of memories Memory at the Brain Systems Level (continued) MTL does not permanently store such conscious memories MTL is not involved in encoding & consolidating other types of memories A series of case reports have led to the postulation of different forms of memory & related neural-memory systems: 1) H.M (Corkin et al. 1997) , 2) K.F (Warrington & Shallice 1969) , 3) M.H Drachman & Arbi, 1966), 4) M.S (Gabrieli et al. 1995). H.M: Bilateral MTLs Surgery HM, a 27-year-old man, underwent bilateral MTL surgery to control epileptic seizures : hippocampal (2/3) regions, amygdala, & the entorhinal cortex. Surgery met the goal, but produced unexpected changes : H.M was unable to form certain type of new memories. (A form of amnesia or memory impairment). H.M is the most tested case in the history of neuropsycholoy. H.M: Bilateral MTLs Surgery (continued) H.M’s cognitive deficits included: 1) Severely impaired memory, but has little or no deficits in other cognitive domains 2) anterograde amnesia 3) Since the time of surgery, his memory impairment was pervasive and generalized to different kind of information & sensory modalities ( part of LTM, called declarative). 4) H.M’s working memory WM) was intact: H.M’s digit span was normal. 5) H.M’s LTM impairment affecting memory of facts & events; semantic & episodic memories. Procedural knowledge was intact (eg. Mirror writing).  H.M’s Memory Impairments: Implications for the MTLs Memory Systems MTLs are necessary for certain memory functions, but not for perceptual, intellectual or executive functions MTLs are necessary for remembering recent events but are not needed for the memory of remote events They are necessary for explicit memory functions regardless of the sensory modalities They are necessary for transferring events and facts into long-term memory storage, but they are not necessary for the current retention of information (WM) MTLs are not necessary for the expression of memories through performance A Taxonomy of Memory Systems Classification based on I. Duration of the memories: Long Term Memory (LTM)- acquisition and recovery of memories over long period Working Memory (WM)- maintenance and manipulation of information for brief periods of time. A Taxonomy of Memory Systems (continued) II. Quality or character of memories: for further classification of LTM Declarative Memory- remembering events or facts, memories that can be verbally “declared”. It depends on conscious awareness, hence, called explicit memory. Non-declarative Memory (NM)- memories expressed through performance, assumed to operate unconsciously (Implicit memory). Further Classification of Declarative and Non-declarative Memories Declarative Memory: Episodic Memory- memory of personally experienced past events Semantic Memory- general knowledge about the world Non-delarative Memory: Procedural memory: refers to implicit memory that can be demonstrated only in performing certain tasks, cannot be explicitly recalled Priming- facilitated processing of a particular stimulus based on previous encounters with the same or related stimulus. Skill learning- gradual improvements in performance as a result of practicing a motor or Working Memory versus Long Term Memory : Supportive Evidence Free recall of a words as a function of its position within a list Working Memory versus Long Term Memory : Supportive Evidence Free recall of words Recency effect Last few words (recency portion of the list) are still in the WM Previous words (the rest of the list) are no longer in WM but recalled from LTM Variables that differentially affect these two components (WM & LTM) suggest dissociation between these two forms of memory: 1) A 30 second distraction between the last word on the list and the recall test eliminates the recency effect (impairs WM) 2) A slower presentation rate enhances recall of most of the list (improves LTM) but does not affect the WM. 3) MTL lesion impair the recall of most of the list Working Memory versus Long Term Memory : Supportive Evidence (continued) An example for Double Dissociation (DD) : MTL lesions tend to impair LTM but not WM, whereas left perisylvian lesions(temporo- parietal) tend to yield the opposite pattern of memory deficits. DD provides support for the idea that WM & LTM depend on largely different anatomical substrates. Figure 13.12 Evidence for different anatomical substrates of working and long-term memory Declarative versus Non-declarative Memory: Supportive Evidence Studies of HM’s performance on memory tasks : impaired DM, Normal Non-declarative memory. Conclusion: some or all MTL structures are important for DM but not for NM.  Declarative versus Non-declarative Memory: Supportive Evidence (continued) Additional evidence from Graf & colleagues (1980s): Amnesic & control subjects studied a list of words At test they were provided with word stems (next slide): 2 test conditions Declarative (explicit) condition: participants were asked to complete the stems with studied words Non-declarative (implicit) version: they were asked to complete them with the first word that came to mind Clear dissociation: Amnesic patients impaired in declarative version of the task but not in the non-declarative version. PRIMING (NM) – an increase in the probability of completing stems with target words when these words were previously encountered in the experiment than when they were not. Effects of amnesia on declarative and non-declarative memory A Taxonomy of Declarative Memory Functions Sub-Categories of Declarative Memory Declarative Memory: Episodic Memory: Memory of events that an individual has experienced personally in a specific place and at a particular time. Semantic Memory: Knowledge about the world that individuals share with other members of their culture, including knowledge of native language and facts learned in school. Sub-Categories of Declarative Memory EM & SM often interact & sometimes overlap Autobiographical memory is a mixture of both EM & SM What you have learned in school can also be remembered as episodes EM: subdivided into RECOLLECTION (with contextual details) & FAMILIARITY (without contextual details) – a fuzzy distinction! Familiarity is closely related to SM or even to the priming  Declarative Memory Tests Episodic Memory Tests Recall tests- partial description of the targets & participants are required to generate the targets (eg, word list free recall) Recognition test- participants are provided with targets intermixed with nontargets & are asked to distinguish the targets. EM tests target different info content item memory, context memory (spatial info, temporal order memory, source memory). Lesion data & imaging data support: context memory is more dependent on hippocampal & prefrontal cortex functions than item memory.  Declarative Memory Tests (continued) Semantic Memory tests Measures of the meaning of words, factual knowledge, properties of objects, etc. Recall tests (What is the capital of the US) Recognition tests (Is Washington the capital….) Verbal fluency test (words that begin with a particular letter, or words in a category) the ability to define the meaning of difficult words (vocabulary tests) The Role of the MTLs in Declarative Memory Within the MTL, the key structure is HIPPOCAMPUS: Its role in DM is not fully understood Normal function of HIPPO are essential for encoding spatial, relational, & Ems. Adjacent structures in MTL are also critical for normal operation of DM HIPPO: important for successfully establishing memory for items in the context The perirhinal cortices influence both memory for items as such and memory for  The Role of Frontal Lobes in Declarative Memory Different structures of FL are associated with different aspects of DM: Episodic retrieval is associated with anterior prefrontal cortex Recollection with activity in the DLPF cortex Familiarity and monitoring with the activation of the RH DLPF regions Left inferior frontal gyrus is active in semantic retrieval  The Role of the Parietal and Posterior Midline Regions in Declarative Memory The posterior lateral parietal & posterior midline regions are involved in episodic retrieval They are deactivated during episodic encoding The role of Sensory Cortices in Declarative Memory These are the loci of the stored memory traces that entail perceptual qualities (appear to be reactivated during retrieval ) These perceptual qualities were stored during encoding