Slowed processing speed contributes to cognitive deficits in amnestic and non‐amnestic mild cognitive impairment

Abstract

AbstractBackgroundMild cognitive impairment (MCI) is characterized by deficits across functional domains, with pronounced memory impairment among amnestic (aMCI) patients. The mixture of cognitive complaints is a challenge in diagnosis and is further complicated by interactions between cognitive domains that are typical for neuropsychological performance.MethodWe aim to examine if slow processing speed may convey MCI‐related deficits across cognitive domains in a sample of African American adults (ages 56‐90): 61 cognitively typical, 28 aMCI, and 14 non‐amnestic MCI. Working memory, executive function, declarative memory and processing speed indices were estimated in structural equation modeling, including indirect effects with bootstrapped 95% confidence intervals (CI).ResultMCI diagnosis predicted deficits in processing speed (b=‐0.53, p=0.02), executive function (b=‐0.37, p=0.03), working memory (b=‐0.62, p=0.001), and episodic memory (b=‐0.61, p<0.001). Slow processing speed predicted low function across domains and in turn partially accounted for effects of diagnosis on executive function (‐0.21, CI:‐0.37/‐0.10), working memory (‐0.12, CI: ‐0.24/‐0.05) and a non‐significant trend for declarative memory (‐0.05, CI: ‐0.15/0.01). Slow processing speed explained approximately 36% of MCI‐related deficits in executive function, 16% in working memory and 8% in declarative memory. In comparison between typical aging and specifically aMCI, processing speed explained deficits in executive function (‐0.19, CI: ‐0.39/‐0.06; 37% indirect) and working memory (‐0.09, CI: ‐0.22/‐0.01; 13%), and a non‐significant trend in declarative memory (‐0.06, CI: ‐0.19/0.00; 8%).ConclusionSlowed processing speed contributes to typical cognitive aging and conveys MCI‐related deficits across domains. Identification of deficits in processing speed may provide insight into MCI progression and opportunities for clinical intervention.