Alterations to task positive and task negative networks during executive functioning in Mild Cognitive Impairment

Abstract

Poor executive functioning increases risk of decline in Mild Cognitive Impairment (MCI). Executive functioning can be conceptualized within the framework of working memory. While some components are responsible for maintaining representations in working memory, the central executive is involved in the manipulation of information and creation of new representations. We aimed to examine the neural correlates of these components of working memory using a maintenance working memory and visuospatial reasoning task. Twenty-five patients with amnestic MCI and 19 elderly controls (EC) completed functional MRI during reasoning and maintenance working memory tasks. In MCI, maintenance working memory was associated with hypoactivation of right frontoparietal regions and hyperactivation of left prefrontal cortex, coupled with attenuation of default mode network (DMN) relative to EC. During reasoning, MCI showed hypoactivation of parietal regions, coupled with attenuation of anterior DMN and increased deactivation of posterior DMN relative to EC. Comparing the reasoning task to the maintenance working memory task yields the central executive. In MCI, the central executive showed hypoactivation of right parietal lobe and increased deactivation of posterior DMN compared to EC. Consistent with prior work on executive functioning, MCI show different neural circuitry during visuospatial reasoning, including changes to both task positive frontoparietal regions, as well as to deactivation patterns within the DMN. Both hyperactivation of task positive networks and increased deactivation of DMN may be compensatory.

Differential Regional Brain Spontaneous Activity in Subgroups of Mild Cognitive Impairment

“…The superior and middle frontal gyri are involved in a series of cognitive processes, such as executive function and working memory (Kim et al, 2014;Zamora et al, 2016), while the lateral temporal cortex is more involved in episodic memory (Luo et al, 2018). These cognitive functions are typically impaired in AD and MCI patients (Bell-McGinty et al, 2005;Clément and Belleville, 2010;Teipel et al, 2010;Liang et al, 2011;Scheller et al, 2014;Verfaillie et al, 2016;Melrose et al, 2018). Studies have suggested an involvement of the lateral frontal and temporal cortical regions in aMCI (Bell-McGinty et al, 2005;Clément and Belleville, 2010;Teipel et al, 2010;Liang et al, 2011;Scheller et al, 2014;Verfaillie et al, 2016;Melrose et al, 2018).…”

“…These cognitive functions are typically impaired in AD and MCI patients (Bell-McGinty et al, 2005;Clément and Belleville, 2010;Teipel et al, 2010;Liang et al, 2011;Scheller et al, 2014;Verfaillie et al, 2016;Melrose et al, 2018). Studies have suggested an involvement of the lateral frontal and temporal cortical regions in aMCI (Bell-McGinty et al, 2005;Clément and Belleville, 2010;Teipel et al, 2010;Liang et al, 2011;Scheller et al, 2014;Verfaillie et al, 2016;Melrose et al, 2018). For instance, a study (Verfaillie et al, 2016) combining the R-fMRI and CSF showed that the regional homogeneity values were associated with the Aβ level of the superior temporal gyrus in patients with sd-aMCI.…”

“…The GM volume in the superior and middle temporal gyri has been used to differentiate the md-aMCI and sd-aMCI as greater volume loss was observed in patients with md-aMCI compared to sd-aMCI (Bell-McGinty et al, 2005). Despite these structural atrophies, several functional MRI studies (Clément and Belleville, 2010;Liang et al, 2011;Melrose et al, 2018) have shown increased activity in the prefrontal and temporal regions in aMCI patients, which has been considered as a compensatory effect for cognitive impairments. It was proposed that the aMCI patients recruited additional brain regions related to cognitive performances to achieve high demanding cognitive tasks (Clément and Belleville, 2010;Liang et al, 2011;Melrose et al, 2018).…”

“…Despite these structural atrophies, several functional MRI studies (Clément and Belleville, 2010;Liang et al, 2011;Melrose et al, 2018) have shown increased activity in the prefrontal and temporal regions in aMCI patients, which has been considered as a compensatory effect for cognitive impairments. It was proposed that the aMCI patients recruited additional brain regions related to cognitive performances to achieve high demanding cognitive tasks (Clément and Belleville, 2010;Liang et al, 2011;Melrose et al, 2018). Together, higher fALFF in the frontal and temporal gyri in sd-aMCI than both the md-aMCI and HC groups suggest a functional compensation in sd-aMCI patients.…”

Impact of 3-Day Combined Anodal Transcranial Direct Current Stimulation-Visuospatial Training on Object-Location Memory in Healthy Older Adults and Patients with Mild Cognitive Impairment

“…Consequently, dependent on individual network excitability, network-level response to stimulation might vary in MCI patients and HE. Suboptimal network activation in MCI patients [93,94] might benefit from activation with atDCS if applied in parallel to training. In line with this hypothesis, initially low-performing HE, that likely also show suboptimal network functioning [95,96], showed greater benefit from atDCS application compared to initially high-performing HE.…”