Abstract
Episodic memory recall processes in Alzheimer's disease (AD) and behavioral variant frontotemporal dementia (bvFTD) can be similarly impaired, whereas recognition performance is more variable. A potential reason for this variability could be false-positive errors made on recognition trials and whether these errors are due to amnesia per se or a general over-endorsement of recognition items regardless of memory. The current study addressed this issue by analysing recognition performance on the Rey Auditory Verbal Learning Test (RAVLT) in 39 bvFTD, 77 AD and 61 control participants from two centers (India, Australia), as well as disinhibition assessed using the Hayling test. Whereas both AD and bvFTD patients were comparably impaired on delayed recall, bvFTD patients showed intact recognition performance in terms of the number of correct hits. However, both patient groups endorsed significantly more false-positives than controls, and bvFTD and AD patients scored equally poorly on a sensitivity index (correct hits—false-positives). Furthermore, measures of disinhibition were significantly associated with false positives in both groups, with a stronger relationship with false-positives in bvFTD. Voxel-based morphometry analyses revealed similar neural correlates of false positive endorsement across bvFTD and AD, with both patient groups showing involvement of prefrontal and Papez circuitry regions, such as medial temporal and thalamic regions, and a DTI analysis detected an emerging but non-significant trend between false positives and decreased fornix integrity in bvFTD only. These findings suggest that false-positive errors on recognition tests relate to similar mechanisms in bvFTD and AD, reflecting deficits in episodic memory processes and disinhibition. These findings highlight that current memory tests are not sufficient to accurately distinguish between bvFTD and AD patients.
Highlights
Alzheimer’s disease (AD) and behavioral variant frontotemporal dementia are the two most common early-onset dementias (Ratnavalli et al, 2002)
The episodic memory deficits in behavioral variant frontotemporal dementia (bvFTD) have been linked to the prominent prefrontal cortex (PFC) changes seen in these patients (Simons et al, 2002b; Pennington et al, 2011), which is suggested to relate to deficits in the organization and implementation of memory retrieval strategies rather than true amnesia or forgetting of encoded material (Kramer et al, 2005)
The current study directly addresses this issue by investigating recognition performance on the Rey Auditory Verbal Learning Test (RAVLT) in bvFTD compared to AD in a large, multi-center sample
Summary
Alzheimer’s disease (AD) and behavioral variant frontotemporal dementia (bvFTD) are the two most common early-onset dementias (Ratnavalli et al, 2002). Hippocampal changes have been found in early-stage bvFTD in terms of post-mortem pathology (Broe et al, 2003; Kril and Halliday, 2004) and along with supporting MTL structures in in vivo imaging studies (Seeley et al, 2008; Whitwell et al, 2009; Hornberger et al, 2012), with the severity of atrophy in these regions sometimes comparable to that found in AD (van de Pol et al, 2006; Rabinovici et al, 2008; Pennington et al, 2011) Beyond these MTL structures, a larger neural network known as the Papez circuit has since been implicated in memory processing. It remains unclear as to how these structural changes in the PFC and Papez memory circuit regions are related to the neuropsychological profile of these patients
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