Functional Neural Correlates of Attentional Deficits in Amnestic Mild Cognitive Impairment

Abstract

Although amnestic mild cognitive impairment (aMCI; often considered a prodromal phase of Alzheimer’s disease, AD) is most recognized by its implications for decline in memory function, research suggests that deficits in attention are present early in aMCI and may be predictive of progression to AD. The present study used functional magnetic resonance imaging to examine differences in the brain during the attention network test between 8 individuals with aMCI and 8 neurologically healthy, demographically matched controls. While there were no significant behavioral differences between groups for the alerting and orienting functions, patients with aMCI showed more activity in neural regions typically associated with the networks subserving these functions (e.g., temporoparietal junction and posterior parietal regions, respectively). More importantly, there were both behavioral (i.e., greater conflict effect) and corresponding neural deficits in executive control (e.g., less activation in the prefrontal and anterior cingulate cortices). Although based on a small number of patients, our findings suggest that deficits of attention, especially the executive control of attention, may significantly contribute to the behavioral and cognitive deficits of aMCI.

Efficiency of Attentional Components in Elderly with Mild Neurocognitive Disorders Shown by the Attention Network Test

“…Compared with healthy group, the NCD-vascular group showed less efficient executive control, and the NCD-AD group not just showed declined executive control but also slowing processing speed. In line with previous studies [9,20], declined executive control was found in adults at high risk for neurodegeneration. However, alerting and orienting were similar between the groups, a result which differed from some studies [7,10].…”

“…However, slowing processing speed and declined orienting were found in subcortical vascular MCI [8]. Further, van Dam et al [9] in 2013 reported that only declined executive control was found in amnestic MCI. Recently, Martella et al [10] in 2014 found impaired alerting in MCI.…”

Depression impairs learning, whereas the selective serotonin reuptake inhibitor, paroxetine, impairs generalization in patients with major depressive disorder

“…However, various studies suggest that amnestic mild cognitive impairment affects many brain systems, other than the medial temporal lobe, and these might contribute to the deficit we found in the generalization phase of the cognitive task (Van Dam et al, 2013). Further, Parkinson’s disease has been shown to affect several systems in the brain other than the nigrostriatal dopamine system (Jellinger, 1991; Mann and Yates, 1983).…”

Magnetic resonance imaging in Alzheimer’s disease and mild cognitive impairment

“…Patients with MCI have demonstrated similar hippocampal deactivation to those with AD during recall [59], but with hyperactivation during encoding phases [60, 61], which might underline mechanistic compensation in prodromal stages. fMRI findings in AD extend to tasks of working memory, visuospatial ability, attention, semantic knowledge, and motor performance [62–66] and in MCI tasks of attention and working memory [62, 64, 67]. …”

“…Increased activation was found for MCI patients relative to control subjectsYetkin et al [62]Task-based fMRI11 AD, 10 MCI, 9 controlsIncreased activation in frontal and temporal regions, fusiform gyrus, and anterior cingulate gyrus was displayed for AD and MCI patients during a working memory task. For selected areas, MCI patients showed greater activation than AD patientsThiyagesh et al [63]Task-based fMRI12 AD, 13 elderly control subjectsDeclines in activation in parietal, parieto-occipital, and premotor cortical areas and increased activation of additional parietal structures was found in AD during an observational visuospatial taskLi et al [64]Task-based fMRI10 AD, 9 MCI, 9 elderly control subjectsReduced activation was found in prefrontal cortical areas for AD patients and increased activation in these same regions was found for MCI patients during a Stoop colour–word interference taskMcGeown et al [65]Task-based fMRI29 AD, 19 controlsNo activation in parietal regions and decreased activation in prefrontal areas was found for AD patients during a semantic knowledge taskVidoni et al [66]Task-based fMRI9 AD, 10 controlsReduced activation was found in the premotor and supplementary motor regions, and the cerebellum, whilst increased activation was evidenced in the primary motor cortices for AD patients during a motor taskVan Dam et al [67]Task-based fMRI8 aMCI, 8 controlsIncreased activation was shown in the tempero-parietal junction, angular gyrus, and precuneus, whereas attenuated activation was seen in prefrontal regions and the anterior cingulate for aMCI patients during an attentional (executive control, alerting and orienting) taskGreicius et al [69]Resting-State fMRI15 AD, 18 controlsReduced connectivity was shown between medial temporal structures and the posterior cingulate cortex for AD patientsDamoiseaux et al [71]Resting-State fMRIBaseline: 21 AD, 18 controlsFollow-up: 11 AD, 10 controlsCompared to control subjects at baseline, declines in connectivity were seen in the posterior DMN and increased activation was found for areas within the ventral and anterior DMN for AD patients. Compared to control subjects at follow-up, decreased connectivity between regions within the anterior, ventral, and posterior DMN in addition to sensorimotor network were shown for AD patients.…”