Differences in spatial and temporal order memory in various neurodegenerative dementias

Editor's Notes

• #1: Ladies and gentlemen, good afternoon. For me it is a great pleasure to be given an opportunity to present the results of our preliminary study aiming to describe differences in spatial and temporal order memory among the most common types of neurodegenerative dementias.
• #2: Here are my disclosures – I have consulted several companies and between 6/2012 and 5/2014 I held a stocks of Polyhymnia-TS.
• #3: Episodic memory impairment is a well known early hallmark of Alzheimer’s disease (AD), but may be also present in other types of dementia such as in Lewy body disease (DLB) or frontotemporal lobar degeneration (FTLD). Studies are, however, not fully consistent whether episodic memory deficits in AD are more pronounced or comparable to episodic memory deficits found in DLB and FTLD.
• #4: The essential components of episodic memory are spatial memory and temporal order memory. These two components have different neural underpinnings – spatial memory in the parahippocampus and temporal order memory in the prefrontal cortex, respectively. These two components are, however, less well understood in neurodegenerative dementias.
• #5: The objective was to compare differences in spatial and temporal components of nonverbal memory among patients with three types of neurodegenerative dementias — Alzeimer‘s disease, frontotemporal lobar degeneration, and Lewy body disease.
• #6: In this cross sectional study we recruited 61 patients with mild AD, 9 patients with DLB and 9 patients with FTLD. Of these 9 FTLD patients were 5 with FTD behavioral variant and 4 with primary progressive afasia, 3 of them with semantic and 1 with non-fluent variant. The subjects underwent a clinical and laboratory evaluation, MRI brain scan with subsequent automated volumetry, detailed neuropsychological examination and testing with an experimental computer test of nonverbal memory called the Episodic-like Memory Test.
• #7: The Episodic-like Memory Test has an advantage to examine both spatial and temporal components of episodic memory simultaneously. In the presentation phase the subjects were asked to remember the positions of pictures and the temporal order in which they were moved into the box. In the testing phase after 5 to 10 minutes delay the subjects were asked to move the pictures back to the initial positions in the same order as they were moved into the box.
• #8: This test includes three successive subtests with increasing levels of difficulty. The positions and temporal orders of pictures in each subtest (with 3, 5 and 7 items) are depicted. For statistical analysis the Kruskall-Wallis one-way analysis of variance and post hoc Mann-Whitney U test with Bonferroni correction were used to evaluate the between-group differences in spatial positions and temporal orders of recalled pictures on each subtest.
• #9: The groups did not differ in education, gender, Mini-Mental State Examination and depression scores (p’s≥.186), but in age (p=.001), where the FTLD group was younger than other two groups (p’s≤.005).
• #10: With the exception of verbal memory the groups were different in all other cognitive functions (language functions approached significance), mainly because the FTLD group was better than other two groups with exception of the verbal fluency, where the FTLD group had the worst scores.
• #11: In the main analysis we found differences among the groups in recalling spatial positions of pictures. The groups were different in spatial positions total score, which is a sum of scores of all three subtests (with 3, 5 and 7 items). Specifically, the FTLD group had a higher total score, which represents better recalling spatial positions of pictures than the AD and DLB groups. Further, the groups were different in scores of each subtest (p’s≤.008). Specifically, the FTLD group performed better than the AD group in all subtests (p’s≤.006) and better than the DLB group in 5-item (p=.007) and 7-item (p=.008) subtests, but not in the 3-item subtest (p=.174). There were no differences between the AD and DLB groups in recalling spatial positions of pictures (p’s≥.187).
• #12: The groups were similar in recalling temporal orders of pictures. They were similar in temporal order total score and in scores of each subtest (p’s≥.117).
• #13: There was a moderate to strong correlation between spatial positions total score and thickness of the left parahippocampal gyrus. Note, that the higher error score was associated with more pronounced thinning of the parahippocampal gyrus. The correlation remained unchanged after adjustment for age, education, gender and MMSE score.
• #14: Further, there was a moderate correlation between temporal order memory total score and thickness of the left prefrontal cortex, where the higher error score was associated with more pronounced thinning of the prefrontal cortex. The correlation also remained unchanged after adjustment for age, education, gender and MMSE score.
• #15: In summary, spatial memory is relatively preserved in patients with FTLD compared to patients with AD and DLB. Our results also suggest that in these patients spatial memory may be associated with thickness of the parahippocampal gyrus. The temporal order memory is similarly affected in patients with AD, FTLD and DLB. Further, our results suggest that in these patients temporal order memory may be associated with thickness of the PFC.
• #16: These findings support the hypothesis that different brain areas are involved in processing of spatial and temporal components of episodic memory. These two components may be unequally impaired in various types of neurodegenerative dementias.
• #17: Finally I would like to thank my colleagues and all patients from the Czech Brain Aging Study who participated at this study and I am prepared to answer your questions. Thank you for your attention.