Investigation of brain functional connectivity in patients with mild cognitive impairment: A functional near‐infrared spectroscopy (fNIRS) study

Abstract

This study examines brain functional connectivity in both cognitively normal seniors and patients with mild cognitive impairment (MCI) to elucidate prospective markers of MCI. A homemade four‐channel functional near‐infrared spectroscopy (fNIRS) system was employed to measure hemodynamic responses in the subjects' prefrontal cortex during a resting state, an oddball task, a 1‐back task, and a verbal fluency task. Brain functional connectivity was calculated as the Pearson correlation coefficients between fNIRS channels. The results show that during the verbal fluency task, while the healthy control (HC) group presents a significantly stronger inter‐hemispheric connectivity compared to intra‐hemispheric connectivity, there is no difference between the inter‐ and intra‐hemispheric connectivity in the MCI group. In addition, a comparison between the MCI and HC connectivity reveals that the MCI group has a statistically higher right and inter‐hemispheric connectivity during the resting state, but a significantly lower left and inter‐hemispheric connectivity during the verbal fluency test. These findings demonstrate the potential of fNIRS to study brain functional connectivity in neurodegenerative diseases.

A Systematic Review of Cerebral Functional Near-Infrared Spectroscopy in Chronic Neurological Diseases—Actual Applications and Future Perspectives

“…MCI patients showed a decreased connectivity compared to HCs most notably in the PFC, as well as positive correlations with cognitive performance assessed by means of the MMSE and the Montreal Cognitive Assessment. Significant differences between MCI patients and HCs in inter-hemispheric connectivity during resting-state, as well as letter and category fluency tasks, were also reported by Nguyen et al [73], thus suggesting that intra-vs. inter-hemispheric connectivity could serve as marker to discriminate MCI from healthy subjects.…”

“…We have therefore focused our attention on the current state-of-the-art of fNIRS applications dealing with motor and cognitive disability in the most frequent chronic neurological disorders of the elderly, namely PD and the AD continuum and MS as the most frequent chronic neurological disease of young and middle-aged adults. Our results reveal that AD and MCI are the most frequently addressed conditions by a wide variety of fNIRS applications, ranging from the monitoring of tissue oxygenation and vasomotor reactivity [65][66][67][68][69][70], to the analysis of resting-state conditions [64,[71][72][73], the assessment of cognitive functions by means of memory and verbal fluency tasks [74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93], visuospatial functions [94,95] and other ecological applications [96,97]. Within the broad context of PD and MS, reviewed studies were more focused on the assessment of motor functions [51,[53][54][55][56]109,110,112].…”

“…In most of the reviewed applications, fNIRS probes were placed over the PFC, as this cortical area is mainly associated with high-level processing functions [ 64 ]. We identified 40 studies performed with a total of 977 AD and 477 MCI patients (208 amnestic MCI), as well as with 792 age-matched HC subjects ( Table 2 ) Most studies were addressed to the monitoring of tissue oxygenation [ 65 , 66 , 67 , 68 , 69 , 70 ], the investigation of functional resting-state activity and connectivity [ 64 , 71 , 72 , 73 ], the assessment of specific cognitive functions [ 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 ] such as visuospatial deficits [ 94 , 95 ] and additional ecological applications [ 96 , 97 ]. Though most studies reported cross-sectional reports, we also retrieved six longitudinal ones [ 98 , 99 , 100 , 101 , 102 , 103 ], thus strongly supporting the idea that fNIRS can represent a viable tool for long-term monitoring of cerebral activity from the early phases of the disease or during rehabilitation.…”

Functional Near-Infrared Spectroscopy and Its Clinical Application in the Field of Neuroscience: Advances and Future Directions

“…A recent systemic review including 36 articles over the past two decades suggests that patients with MCI and AD have impaired frontal and long-range connectivity in the resting state fMRI ( Yeung and Chan, 2020 ), which was also observed in a recent study ( Yoo and Hong, 2019 ). Task-related functional connectivity analysis suggests that the number and strength of prefrontal functional connections increased during a working memory task ( Yu et al, 2020 ) but left and inter-hemispheric connectivity during a verbal fluency test were lower ( Nguyen et al, 2019 ) in the patients with MCI compared to healthy controls. This could indicate the use of compensatory mechanisms in the prefrontal cortex as a result of impaired default connectivity in MCI patients.…”

Quantitative Assessment of Resting-State for Mild Cognitive Impairment Detection: A Functional Near-Infrared Spectroscopy and Deep Learning Approach

“…Through studies over the past decade, researchers have demonstrated the feasibility of using fNIRS to identify reduced cerebral oxygenation either in the resting state or the task period, such as during word retrieval, memory tasks, motor tasks, and visuospatial perception [28]. In the resting-state cases, altered connectivity [29][30][31] and fluctuations [32][33][34][35][36] of cerebral oxygenation have been reported in MCI and AD groups. This difference is associated with the dysregulation of information integration in the patient's brain.…”