Physical changes
Structural and functional MRI imaging show a characteristic pattern of atrophy in the temporal lobes (predominantly on the left), with inferior greater than superior involvement and anterior temporal lobe atrophy greater than posterior. This distinguishes it from Alzheimers disease. Meta-analyses on MRI and FDG-PET studies confirmed these findings by identifying alterations in the inferior temporal poles and amygdalae as the hotspots of disease - brain regions that have been discussed in the context of conceptual knowledge, semantic information processing, and social cognition. Based on these imaging methods, semantic dementia can be regionally dissociated from the other subtypes of frontotemporal lobar degeneration, frontotemporal dementia, and progressive nonfluent aphasia.Selective hypometabolism of glucose has been observed in the anterior temporal lobe, as well as the medial temporal lobe and limbic areas.Damage to white matter tracts connecting the anterior temporal cortex to the inferior longitudinal, arcuate, and uncinate fasciculi, which are regions of the language network, is also seen using diffusion tensor imaging. Imaging also shows the integrity of the axonal connections from the anterior temporal cortex to frontal and posterior associative areas to be altered.Functional abnormalities have also been observed in hippocampal structures, the ventromedial prefrontal cortex, and the cingulate cortex. Memory in dementia: musical objects, musical concepts, and semantic memory
Melodies are a key aspect of musical objects that are thought to form the contents of semantic memory for music. Melodies are defined as familiar tunes that become associated with musical or extra musical meaning.
Using familiar songs, such as Christmas carols, were used to test whether SD patients were able to recognize the tones and melodies of the songs if the patients were just given the words of the song. In the analysis of semantic memory using melodies as stimuli, the contents of semantic memory can include many other aspects aside from recognition of the melody, such as the general information about the music (composer, genre, year of release). Results have shown that musicians who have semantic dementia are able to identify and recognize certain melodic tones.Further exploring the tests of music and semantic memory, results of a study that centered on the comprehension of emotion in music indicated that Alzheimers Disease (AD) patients retained the ability to discern emotions from a song while non-AD degenerative disease patients, such as those with semantic dementia (SD), show impaired comprehension of these emotions. Moreover, several dementia patients, all with varied musical experience and knowledge, all demonstrated an understanding of the fundamental governing rules of western music. Essentially, it was found that superordinate knowledge of music, such as the rules of composition, may be more robust than knowledge of specific music.Regarding the neurobiological correlates for this study, it was determined, via lesion studies, that bilateral (but especially the left-side of the brain) fronto-temporoparietal areas are significant in the associative processing of melodies.