Relationship between Episodic and Semantic Memory - Assignment Example

Semantic Dementia on the Relationship Between Episodic And Semantic Memory Your name Institutional Affiliations There has been considerable controversy amongst neuroscientists over the last 25 years over the cognitive and neural organization of long-term memory. Tulving proposed the fractionation of memory into two different types, episodic and semantic in one of the earliest and most influential theories of long-term memory (Grahama et al., 2000). Episodic memory refers to our repository of personally experienced events, the retrieval of which needs conscious recollection of the exact temporal partial setting of an episode from the past. On the other hand, semantic memory applies to our store of culturally-shared general knowledge regarding the world including the meaning of words, facts, concepts, objects and people. This kind of information does not need recollection of when and where it was learnt initially unlike episodic memory (Tulving, 2009). According to Grahama et al. (2000), episodic and semantic memory were considered in Tulvign’s original conception of long-term memory psychologically and neurologically different, a dichotomy reflecting the manner in which human brain is supposed to obtain, process, and store information. Initially, it was thought that patients with amnesia who show impaired new episodic learning although the fractionation spared semantic knowledge however, this view have been challenged by recent studies. Nyberg & Tulving (2006) assert that Tulving revised his model so as to account for the evidence against a simple dissociation between episodic and semantic memory suggesting that episodic memory is a subsystem of semantic memory and is, hence, reliant upon the integrity of semantic knowledge. This hierarchical view has been expanded by the most recent instantiation of his theory known as SPI- Serial encoding, Parallel storage, and Independent retrieval. There are four main groups of cognitive memory system in this theory including perceptual representation; semantic; working; and episodic memory. This theory has three crucial premises including: (1) information is encoded into system serially, with encoding in one system dependent upon output from the previous stage (Nyberg & Tulving, 2006). (2) Information can be stored in different systems in parallel; and (3) information in different systems can be retrieved independently without any impacts on retrieval of information from other systems. This concept describes why an amnesia patient- deficit of episodic memory- may still be capable of retrieving semantic information that was acquired earlier in life. Parkin (2005) stipulates that due to the fact that there was inadequate evidence until recently that patients could be presented with a selective impairment to semantic memory Tulving’s prediction regarding the dependence of new learning on semantic memory has never been tested specifically. A newly described syndrome called semantic dementia, which results in a progressive, relatively selected deterioration of semantic memory has rectified this situation. A century ago, pick noted that patients with neurodegenerative disease could show a focal cognitive deficit like impaired language (Parkin, 2005). Mesulam reported six patients with slowly progressing aphasia, some of whom showed fluent and articulate speech which notably consisted of few word contents some 90 years following this initial description. This economic pattern has been illustrated to reflect a progressive breakdown in the central store of semantic memory affecting both and non-verbal aspects of conceptual skills about objects, concepts, people, facts, and the meaning of words. Patient with semantic dementia end up performing poorly on any task which requires semantic knowledge, such as pictures naming, category fluency, word-picture matching, defining and drawing concepts in relation to their names, selecting the write color of white and black line drawing and sorting words or pictures according to the pre-specified criterion (Grahama et al., 2000). By contrast, performance on the test of measuring other cognitive domains, such as the syntactic aspects of language, phonological, non-verbal; problem solving, working memory, visual-spatial and perceptual abilities, is relatively unaffected, even at relative late stage of disease. Press et al. (2008) stipulate that according to Neuroradiological investigations in semantic dementia, it reveals that focal atrophy of the antero-lateral aspect of temporal lobes, especially the pole and inferior and the one that is in the middle temporary gyri areas, with sparing of the hippocampal complex. Recently, during the study of neuroimaging study, in which regional cerebral blood flow was measured in four patients with semantic dementia as they performed a semantic decision task, the patients showed a significant decrease in activity in the left posterior inferior temporal gyrus compared to the control subjects (Press et al., 2008). The imaging results suggest that, a structural and a functional disruption to the temporal lobes in semantic dementia. However, their has being relatively little neuropathological data collected in the diseases, a meta analysis of the published and un published information for 13 cases which revealed that all patients had either classic pick’s disease pathology or non-specific neuronal loss without characteristic pick or Alzheimer histological markers. According to Press et al. (2008), the nature of the semantic memory impairment in semantic memory impairment in semantic dementia presents cognitive neuropsychologists with a unique opportunity so that to investigate the cognitive and neural organization of long term memory. Recent experiment has found evidence for a reverse temporal gradient. These studies are important because they hint at the possibility that, at least at an early stage in the disorder, new learning tend to become normal, a finding which would have fundamental implications for our understanding of the nature of episodic and semantic memory (Grahama et al., 2000). The first experiment that was carried out was about episodic and semantic memory in patients with semantic dementia and in amnesic patients with a much presumed early Alzheimer disease. In particular, we related the patients ability to name a picture of a familiar object during the study phase so that to recognize memory for either the identical item or a perceptually different exemplar of the same object. Tulving (2009) asserts that the essence of our hypothesis is that new learning is based on a combination of sensory information provided by the learning event and semantic information about the content of the event. If the target that comes from the study phase of recognition memory experiment is replaced at test by perceptual different exemplar. This manipulation should reduce the usefulness of perceptual information and place more demands on input from semantic memory (Tulving, 2009). Therefore, the patients with semantic dementia would show relatively preserved recognition memory in a perceptual identical condition but their ability to select the target item in the perceptually different condition would be reduced relatively so that to control the performance as a result of the patients impaired conceptual knowledge of the items. Nyberg & Tulving (2006) state that the amnesic patient with presumed early Alzheimer’s disease presented with a history of a progressive decline in the new learning of the verbal and non verbal material. Neuropsychological testing demonstrated that the group was performed as well as control participant on most tests of semantic memory. The patients were markedly impaired on test of episodic memory, such as the recognition of the Rey Complex Figure but hard working memory and visuo-perceptual skills within the normal range (Grahama et al., 2000). Neuroimaging is a coronally oriented MRI scans for the patients with semantic dementia reveal focal atrophy to one or both infero-lateral temporal lobe, with a relative preservation of the hippocampal complex. Coronally oriented MRI scans for the amnesic patients with presumed early Alzheimer’s disease showed selective hippocampal atrophy, with an average little involvement of the lateral temporal lobes (Grahama et al., 2000). Generally, a model of a long term memory in which episodic memory takes input solely cannot explain why patients with semantic dementia can, under certain conditions, show normal new episodic learning. Instead, our result found argue that inputs from different neocortical areas in the brain, which subserve perceptual analysis and semantic memory, work in concert to support new learning. This approach provides a more parsimonious explanation than other views for the patterns of results found in both the normal and neuropsychology memory literatures (Hodges & Graham, 2008). Furthermore, this research clearly demonstrate that patient semantic dementia provide cognitive neuropsychologist with an unprecedented opportunity so that to investigate the architecture of long term memory, and to advance our understanding of how the human brain acquires, stores and retrieves episodic and semantic information. The idea of the gradual cortical consolidation is compatible with poor retrieval of recent and better preserved distance and with the opposite gradient recently demonstrated for semantic dementia. References Grahama, K., Simonsa, J., Pratta, K., Pattersona, K. and Hodgesa, J. (2000). Insights from semantic dementia on the relationship between episodic and semantic memory. Neuropsychologia 38 (2000) 313-324 Hodges, R. and Graham, S. (2008). A reversal of the temporal gradient for famous person knowledge in semantic dementia: implications for the neural organisation of long-term memory. Neuropsychologia 36, 2008, 803-825. Nyberg, L. and Tulving, E. (2006). Classifying human long-term memory: Evidence from converging dissociations. European Journal of Cognitive Psychology 8, 2006, 163-83. Parkin, J. (2005). Residual learning capability in organic amnesia. Cortex 18, 2005, 417-440. Press, A., Amaral, G. and Squire, R. (2008). Hippocampal abnormalities in amnesic patients revealed by high-resolution magnetic resonance imaging. Nature 341, 2008, 54-57. Tulving, E. (2009). Elements of episodic memory. Oxford: Clarendon Press. Read More