Background: Subjective Cognitive Decline (SCD) is the early preclinical stage of Alzheimer's
Disease (AD). Previous study provided an invaluable contribution by showing that a tactile
angle discrimination system can be used to distinguish between healthy older individuals and patients
with mild cognitive impairment and AD. However, that study paid little attention to the relationship
between tactile angle discrimination and SCD. Therefore, a means of differentiating Normal Controls
(NCs), elderly subjects with SCD, patients with amnestic Mild Cognitive Impairment (aMCI), and AD
is urgently needed.
Methods: In the present study, we developed a novel tactile discrimination device that uses angle stimulation
applied to the index finger pad to identify very small differences in angle discrimination between
the NC (n = 30), SCD (n = 30), aMCI (n = 30), and AD (n = 30) groups. Using a three-alternative
forced-choice and staircase method, we analyzed the average accuracy and threshold of angle
Results: We found that accuracy significantly decreased while thresholds of angle discrimination increased
in the groups in the following order: NC, SCD, aMCI, and AD. The area under the receiver operating
characteristic curve also indicated that the tactile angle discrimination threshold was better than
Mini-Mental State Examination scores in distinguishing NC individuals and SCD patients.
Conclusion: These findings emphasize the importance of tactile working memory dysfunction in explaining
the cognitive decline in angle discrimination that occurs in SCD to AD patients and offer further
insight into the very early detection of subjects with AD.