Profiles of cognitive impairment in the continuum from normal cognition to Alzheimer's clinical syndrome: Contributions of the short-term memory binding tests.

BACKGROUND: Short-term memory binding (STMB) tests assess conjunctive binding, in which participants should remember the integration of features, such as shapes (or objects) and colors, forming a unique representation in memory. In this study, we investigated two STMB paradigms: change detection (CD) and free recall (FR). OBJECTIVE: To investigate the cognitive profile in the CD and FR tasks of three diagnostic groups: cognitively unimpaired (CU), mild cognitive impairment (MCI), and Alzheimer's clinical syndrome (ACS). In addition, we aimed to calculate and compare the accuracy of the CD and FR tasks to identify MCI and ACS. METHODS: Participants were 24 CU, 24 MCI, and 37 ACS. The cognitive scores of the clinical groups were compared using analysis of variance (ANOVA) and receiver-operating characteristic (ROC) analyses were carried out to verify the accuracy of the STMB tasks. RESULTS: In the CD task, CU was different from MCI and ACS (CU > MCI = ACS), while in the FR task all groups were different (CU > MCI > ACS). The ROC analyses showed an area under the curve (AUC) of 0.855 comparing CU with MCI for the CD task and 0.975 for the FR. The AUC comparing CU and ACS was 0.924 for the CD and 0.973 for the FR task. The FR task showed better accuracy to identify MCI patients, and the same accuracy to detect ACS. CONCLUSION: The present findings indicate that impairments in CD and FR of bound representations are features of the cognitive profiles of MCI and ACS patients.

Recalling feature bindings differentiates Alzheimer's disease from frontotemporal dementia.

It has been challenging to identify clinical cognitive markers that can differentiate patients with Alzheimer's disease (AD) from those with behavioral variant frontotemporal dementia (bvFTD). The short-term memory binding (STMB) test assesses the ability to integrate colors and shapes into unified representations and to hold them temporarily during online performance. The objective of this study is to investigate whether free recall deficits during short-term memory binding (STMB) test can differentiate patients with AD from those with bvFTD and controls. Participants were 32 cognitively intact adults, 35 individuals with AD and 18 with bvFTD. All patients were in the mild dementia stage. Receiver-operating characteristic (ROC) analyses were used to examine the diagnostic accuracy of the STMB. The results showed that AD patients performed significantly worse than controls and bvFTD patients in the STMB test, while the latter groups showed equivalent performance. The bound condition of the STMB test showed an AUC of 0.853, with 84.4% of sensitivity and 80% of specificity to discriminate AD from controls and an AUC of 0.794, with 72.2% of sensitivity and 80% of specificity to differentiate AD from bvFTD. Binding deficits seem specific to AD. The free recall version of the STMB test can be used for clinical purposes and may aid in the differential diagnosis of AD. Findings support the view that the STMB may be a suitable cognitive marker for AD.