Altered Neural Activity during Semantic Object Memory Retrieval in Amnestic Mild Cognitive Impairment as Measured by Event-Related Potentials

Abstract

Deficits in semantic memory in individuals with amnestic mild cognitive impairment (aMCI) have been previously reported, but the underlying neurobiological mechanisms remain to be clarified. We examined event-related potentials (ERPs) associated with semantic memory retrieval in 16 individuals with aMCI as compared to 17 normal controls using the Semantic Object Retrieval Task (EEG SORT). In this task, subjects judged whether pairs of words (object features) elicited retrieval of an object (retrieval trials) or not (non-retrieval trials). Behavioral findings revealed that aMCI subjects had lower accuracy scores and marginally longer reaction time compared to controls. We used a multivariate analytical technique (STAT-PCA) to investigate similarities and differences in ERPs between aMCI and control groups. STAT-PCA revealed a left fronto-temporal component starting at around 750 ms post-stimulus in both groups. However, unlike controls, aMCI subjects showed an increase in the frontal-parietal scalp potential that distinguished retrieval from non-retrieval trials between 950 and 1050 ms post-stimulus negatively correlated with the performance on the logical memory subtest of the Wechsler Memory Scale-III. Thus, individuals with aMCI were not only impaired in their behavioral performance on SORT relative to controls, but also displayed alteration in the corresponding ERPs. The altered neural activity in aMCI compared to controls suggests a more sustained and effortful search during object memory retrieval, which may be a potential marker indicating disease processes at the pre-dementia stage.

Common and differential electrophysiological mechanisms underlying semantic object memory retrieval probed by features presented in different stimulus types

“…Behaviorally, nonretrieval trials had longer RT and better accuracy compared to retrieval trials. These effects have been consistently shown in all previous SORT studies using only visual words as stimuli (Brier et al, 2008;Chiang et al, 2014Chiang et al, , 2015. As proposed before, this difference between conditions may indicate a longer and more exhaustive search in non-retrieval compared to retrieval trials that is required before making a decision (Chiang et al, 2014); this search seems to last even longer in the verbal domain (VW and AW) compared to the nonverbal domain (Pic) when non-retrieval RT was considered.…”

“…Parameters of stimulus timing are noted at bottom. Chiang et al, 2015). These statistical analyses were performed in the SAS software 9.4 using Proc Mixed, and the variances associated with subject variability, b j(i) , and trial variability, ε ijkl , were also estimated by restricted maximum likelihood.…”

“…ERP derive from averaging of EEG epochs to capture consistent changes in phase-locked neural activity as reflected in the timing and shape of ERP waveforms (Luck, 2005). To date, several neurophysiological studies using either technique have been performed to examine semantic object memory retrieval during SORT (Ferree et al, 2009;Brier et al, 2008;Chiang et al, 2014Chiang et al, , 2015.…”

The Role of Physical Fitness in the Neurocognitive Performance of Task Switching in Older Persons with Mild Cognitive Impairment

“…Importantly, the improved cardiorespiratory fitness was associated with improved executive function for aMCI women [48]. These substantial findings suggest that although elderly people with aMCI had declines in executive control processes as a function of neuropathological aging [20,29,[33][34][35], they still exhibited cognitive and neural plasticity and their task-switching deficits appear amendable to an intervention based on increased physical activity.…”

“…There is a growing body of research that supports the presence of an early executive functioning deficit in persons with aMCI [21,29,[33][34][35]. Task switching is an executive function that is needed to master a wide array of daily tasks, and thus is suitable for examining age-related effects on the abilities to represent, maintain, and update contextual information in working memory [36].…”