Working memory and mild cognitive impairment: Digital intra‐response latency, subcortical nuclei, and neuropsychological test performance

Abstract

AbstractBackgroundDigital technology offers the ability to obtain nuanced data previously unobtainable. A digital Backward Digit Span (BDT) using voice recognition was administered to memory clinic patients. Our goal was to assess the validity of this technology by (1) analyzing differences between non‐MCI versus MCI patients; (2) examining correlations with other neuropsychology tests; and, (3) analyzing test performance in relation to MRI subcortical regions of interest known to be related to working memory.MethodJak‐Bondi (2009) criteria classify patients into MCI (n= 67) and non‐MCI (n= 72) groups. Working memory (WM) was assessed with the Backward Digit Span Test (BDT) consisting of 7 trials of 5 digits backwards; all trials were administered; and comprehensive neuropsychological testing was obtained. Only correct test trials were analyzed. BDT variables of interest included latency for each five responses. NeuroquantTM software calculated thalamic, caudate and hippocampal volume (n= 23) controlled for intracranial volume (ICV).ResultBetween‐group difference for total time to completion was not significant (M= 55.64 + 18.91 sec.). An analysis of serial order position latencies clearly suggests two distinct epochs (Figure 1). A latency ratio (LR) for serial order 1 versus serial order 3 was calculated. Using this measure, non‐MCI patients presented with slower latency to initiate their response (serial order 1); but faster latency to sustain their response (serial order 3) compared that MCI patients (F[1,52]= 6.26, p< .016). Simple correlations were significant between the BDT‐LR and Judgement of Line Orientation Oblique test items (r= 0.325, p< .019) and WAIS‐III Digit Symbol test performance (r= 0.316, p< .017). Simple correlations were significant or near significant between the BDT‐LR and left thalamic volume (r= 0.468, p< 0.032); right thalamic volume (0.410, p< .065); total thalamic volume (r= 0.470, p< 0.032); and left caudate volume (r= 0.447, p< .042).ConclusionThese data are remarkable for how patients allocate their time to generate a correct response. Correlations between BDT‐LR, subcortical nuclei, and neuropsychological test performance provide evidence for the validity of using discrete latency measures to assess WM in patients with MCI. Intra‐response BDT latency ratios could be a meaningful neurocognitive biomarker for emergent illness.