Decreased activities of prefrontal and temporal lobes in patients with mild cognitive impairment and mild Alzheimer’s disease on a clock drawing task via functional near‐infrared spectroscopy imaging

Abstract Background Studies have shown that changes in cerebral blood flow occur in the early stage of dementia, including Alzheimer’s disease (AD), and decreased cerebral blood flow contributes to impairment of brain activities, then affects cognitive function. To diagnose AD in very early stage, such as mild cognitive impairment (MCI), it is therefore necessary to find a new way to detect early activities of brain, such as functional near‐infrared spectroscopy (fNIRS). Methods The clock drawing task (CLOX) is one of the widely used neurocognitive function scoring test for dementia. In this study, brain activities were examined in patients with MCI (n = 8) and mild AD (n = 8) during an unprompted CLOX drawing using functional near‐infrared spectroscopy (fNIRS). The concentration changes of oxyhemoglobin (HbO), reflecting brain activities indirectly, were tested in each group via fNIRS. Results Activation in the right hemisphere was significantly attenuated in mild AD compared with MCI. With the development of disease severity from MCI to mild AD, the reductions of HbO2 concentrations in the right prefrontal and right temporal lobe were observed greater and steeper. The HbO2 in mild AD was significantly lower than that in MCI (false discovery rate corrected, p <0.025). In addition, HbO2 concentration was positively associated with the clinical score of MMSE (MCI group, p<0.05; mild AD group, p<0.05). Conclusion This study suggests that activity in the frontal and temporal lobes of mild AD is reduced compared to MCI. Those results reflects that CLOX is an effective tool for extracting fNIRS signal features. In addition, fNIRS‐based analysis has great promise for exploring the mechanisms of changes in the sensory‐spatial function of MCI and mild AD.