Neurocognitive Constructs Underlying Executive Control in Statistically-Determined Mild Cognitive Impairment

Background: The model of executive attention proposes that temporal organization, i.e., the time necessary to bring novel tasks to fruition is an important construct that modulates executive control. Subordinate to temporal organization are the constructs of working memory, preparatory set, and inhibitory control. Objective: The current research operationally-defined the constructs underlying the theory of executive attention using intra-component latencies (i.e., reaction times) from a 5-span backward digit test from patients with suspected mild cognitive impairment (MCI). Methods: An iPad-version of the Backward Digit Span Test (BDT) was administered to memory clinic patients. Patients with (n = 22) and without (n = 36) MCI were classified. Outcome variables included intra-component latencies for all correct 5-span serial order responses. Results: Average total time did not differ. A significant 2-group by 5-serial order latency interaction revealed the existence of distinct time epochs. Non-MCI patients produced slower latencies on initial (position 2-working memory/preparatory set) and latter (position 4-inhibitory control) correct serial order responses. By contrast, patients with MCI produced a slower latency for middle serial order responses (i.e., position 3-preparatory set). No group differences were obtained for incorrect 5-span test trials. Conclusion: The analysis of 5-span BDT serial order latencies found distinct epochs regarding how time was allocated in the context of successful test performance. Intra-component latencies obtained from tests assessing mental re-ordering may constitute useful neurocognitive biomarkers for emergent neurodegenerative illness.