Reduced Frontal Activations at High Working Memory Load in Mild Cognitive Impairment: Near-Infrared Spectroscopy

Abstract

Background: Some functional magnetic resonance imaging studies have reported altered activations in the frontal cortex during working memory (WM) performance in individuals with mild cognitive impairment (MCI), but the findings have been mixed. The objective of the present study was to utilize near-infrared spectroscopy (NIRS), an alternative imaging technique, to examine neural processing during WM performance in individuals with MCI. Methods: Twenty-six older adults with MCI (7 males; mean age 69.15 years) were compared with 26 age-, gender-, handedness-, and education-matched older adults with normal cognition (NC; 7 males; mean age 68.87 years). All of the participants undertook an n-back task with a low (i.e., 0-back) and a high (i.e., 2-back) WM load condition while their prefrontal dynamics were recorded by a 16-channel NIRS system. Results: Although behavioral results showed that the two groups had comparable task performance, neuroimaging results showed that the MCI group, unlike the NC group, did not exhibit significantly increased frontal activations bilaterally when WM load increased. Compared to the NC group, the MCI group had similar frontal activations at low load (p > 0.05 on all channels) but reduced activations at high load (p < 0.05 on 4 channels), thus failing to demonstrate WM-related frontal activations (p < 0.05 on 9 channels). In addition, we found a positive correlation between the left WM-related frontal activations and WM ability primarily in the NC group (r_s = 0.42, p = 0.035), suggesting a relationship between frontal hypoactivation and WM difficulties. Conclusion: The present findings suggest the presence of frontal dysfunction that is dependent on WM load in individuals with MCI.

Decreased Fronto-Parietal and Increased Default Mode Network Activation is Associated with Subtle Cognitive Deficits in Elderly Controls

“…Recent studies using near-infrared spectroscopy also indicated decreased frontal activation at high WM load in MCI cases and suggested an association between frontal hypoactivation and WM difficulties[13]. In the same line, an altered frontal lateralization that impact on verbal fluency performances in MCI cases was recently reported [37]. Moreover, MCI cases exhibit increased difficulties in modulating FPN activation that usually decreases after cognitive training to guarantee processing efficiency in healthy controls [38].…”

Functional imaging of cognition in an old-old population: A case for portable functional near-infrared spectroscopy

“…However, individuals with mild cognitive impairment may produce decreased oxyhemoglobin concentrations. [38, 39] Thus it appears that using portable cognitive testing and neuroimaging methods such as fNIRS may help to document evolving cognitive impairments in at-risk populations living in the community.…”

Cerebral Hemodynamics in Mild Cognitive Impairment: A Systematic Review

“…The mean age of participants varied between 57-80 years, and few had an equal gender split between participants. All studies reported MMSE except four [15,64,68,69]. All participants had an MMSE >24, or equivalent, except one study (mean MMSE 23.7) [54].…”

“…All studies lacked sample size calculations, and few demonstrated testing for validity and reliability ( Supplementary Figures 1 and 2). Twenty-two of the 26 studies were cross sectional [15,18,20,40,47,48,[53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69], and the remaining four studies were longitudinal [50][51][52]60] (two mixed design) [52,60]. Follow-up time in the longitudinal studies ranged from five weeks to two years [50][51][52]60].…”

“…Sample sizes were small for most studies (total sample size range: 15-127). The diagnostic classification system used for MCI varied between studies, five had no formal criteria [18,20,47,53,68], the majority used the Petersen criteria (n = 14) [40,48,51,52,54,[56][57][58][59][60][61][62]67], and fewer used the Mayo [50,55], Winbald [65], Jak [15,64,69], and Reisberg [66] criteria. Several studies had extensive exclusion of other neurodegenerative, psychiatric conditions [15, 48, 50-52, 57-60, 62, 63, 66, 67] and psychotropic medications [59,62,67].…”