Excessive compensatory recruitment as a compulsory neurophysiological mechanism in Very Early Alzheimer's Disease as compared to Mild Vascular Dementia and to age-matched normal controls

Cognitive workload across the spectrum of cognitive impairments: A systematic review of physiological measures

“…Consistent with EEG/MEG findings in patients with MCI, patients with AD in the early stages needed more effort to perform the cognitive task compared to healthy older adults (Beuzeron-Mangina & Mangina, 2009;Hidasi et al, 2007;van der Hiele et al, 2007;van Deursen et al, 2011van Deursen et al, , 2008. Event-related potential components (ERPs) are measured by EEG.…”

“…Patients with AD showed greater cognitive workload accompanied with decreased behavioral performances during the cognitive task compared to older adults with MCI or healthy older adults (Leyhe et al, 2009;Saur et al, 2010;Sole-Padulles et al, 2009;van der Hiele et al, 2007;van Deursen et al, 2011;van Deursen et al, 2008). The higher amount of alpha 2 band after the task, the increased local gamma band power and early gamma band power, the higher P450 amplitudes over parietal and occipital sites, the over-activation or additional activation of specific regions in patients with AD were used as compensatory mechanisms for their cognitive decline (Beuzeron-Mangina & Mangina, 2009;Hidasi et al, 2007;Leyhe et al, 2009;Saur et al, 2010;Sole-Padulles et al, 2009;van Deursen et al, 2011van Deursen et al, , 2008.…”

“…ERPs during a number-letter task were especially useful to detect patients with probable AD at an early stage (Chapman et al, 2007). Patients in very early stages of AD displayed abnormally high P450 amplitudes over parietal and occipital sites as opposed to healthy older individuals that may be explained by compensatory recruitment in parieto-occipital areas (Beuzeron-Mangina & Mangina, 2009). Another EEG study analyzed the brain activity before and after the execution of a cognitive task (Hidasi et al, 2007).…”

Neural Dynamics of Multiple Object Processing in Mild Cognitive Impairment and Alzheimer’s Disease: Future Early Diagnostic Biomarkers?

“…In the context of EEG studies, parieto-occipital compensatory recruitment in MCI patients has been reported as an abnormal enhancement of P450 amplitude over posterior regions during a memory task, indicating that MCI patients need to recruit additional resources in order to carry out the task [51]. Crucially, this compensatory mechanism has been observed only in the prodromal phase of AD but not in the later stages when the diagnosis of AD had taken hold [51]. In line with this result, in the present study we found that the supposed compensatory mechanism exhibited as a more pronounced CDA component in MCI patients was no longer present in AD patients, who conversely showed a suppression of the aforementioned component.…”

“…In line with this result, in the present study we found that the supposed compensatory mechanism exhibited as a more pronounced CDA component in MCI patients was no longer present in AD patients, who conversely showed a suppression of the aforementioned component. Thus, the severe neurodegeneration of the dementia phase may prevent the recruitment of additional neural resources, and may not allow compensatory mechanisms to take place as the pathological burden becomes more severe [51,52]. These conclusions are consistent with the findings of functional activation studies reviewed by Prvulovic and colleagues [53], who demonstrated that the progression of neural degeneration can lead to phenomena of either hyper-activation (usually associated with mildly impaired performance, as in the case of MCI patients in our study), or hypo-activation, which is linked to a greater impairment in the performance (as showed here for AD patients).…”