Semantic dementia (SD), also known as semantic variant primary progressive aphasia (svPPA), is a progressive neurodegenerative disorder characterized by loss of semantic memory in both the verbal and non-verbal domains. However, the most common presenting symptoms are in the verbal domain (with loss of word meaning). Semantic dementia is a disorder of semantic memory that causes patients to lose the ability to match words or images to their meanings. However, it is fairly rare for patients with semantic dementia to develop category specific impairments, though there have been documented cases of it occurring. Typically, a more generalized semantic impairment results from dimmed semantic representations in the brain.SD is one of the three canonical clinical syndromes associated with frontotemporal lobar degeneration (FTLD), with the other two being frontotemporal dementia and progressive nonfluent aphasia. SD is a clinically defined syndrome but is associated with predominantly temporal lobe atrophy (left greater than right) and hence is sometimes called temporal variant FTLD (tvFTLD). SD is one of the three variants of primary progressive aphasia (PPA), which results from neurodegenerative disorders such as FTLD or Alzheimers disease. It is important to note the distinctions between Alzheimers disease and semantic dementia with regard to types of memory affected. In general, Alzheimers disease is referred to as a disorder affecting mainly episodic memory, defined as the memory related to specific, personal events distinct for each individual. Semantic dementia generally affects semantic memory, which refers to long-term memory that deals with common knowledge and facts.
Based on the data of imaging studies that looked at the localization of processing melodies, it can be inferred that the anatomical location of the processes in consistent with the findings that some SD patients have intact melody recognition. Additionally, the neurobiological basis for musical emotion identification implicated the limbic and paralimbic structures in this process. Overall, the results of these studies suggest that the neurobiological basis of musical semantic memory is bilaterally located in the cerebral hemispheres, likely around the fronto-temporal areas of the brain. Unfortunately, due to the lack of studies studying musical semantic memory, conclusions cannot be more specific. Treatment
There is currently no known curative treatment for SD. The average duration of illness is 8–10 years, and its progression cannot be slowed. Progression of SD can lead to behavioral and social difficulties, thus supportive care is essential for improving quality of life in SD patients as they grow more incomprehensible. Continuous practice in lexical learning has been shown to improve semantic memory in SD patients. No preventative measures for SD are recognized. References
Reference 20: Rohani Omar, Julia C. Halistone, and Jason D. Warren, "Semantic Memory for Music in Dementia," Music Perception 29, no. 5 (June 2012):, doi:10.1525/mp.2012.29.5.467.Reference 21:Lise Gagnon, Isabelle Peretz, and Tamàs Fülöp, "Musical structural determinants of emotional judgments in dementia of the Alzheimer type.," Neuropsychology 23, no. 1 (2009): doi:10.1037/a0013790.Reference 22: J. C. Hailstone, R. Omar, and J. D. Warren, "Relatively preserved knowledge of music in semantic dementia," Journal of Neurology, Neurosurgery & Psychiatry 80, no. 7 (2009): doi:10.1136/jnnp.2008.153130.