Abstract
The integrity of the frontal areas of the brain, specifically the prefrontal cortex, are critical to preserve cognition and mobility in late life. Prefrontal cortex regions are involved in executive functions and gait control and have been related to the performance of dual-tasks. Dual-task performance assessment may help identify older adults at risk of negative health outcomes. As an alternative to neuroimaging techniques that do not allow assessment during actual motion, functional Near-Infrared Spectroscopy (fNIRS) is a non-invasive technique that can assess neural activation through the measurement of cortical oxygenated and deoxygenated hemoglobin levels, while the person is performing a motor task in a natural environment as well as during cognitive tasks. The aim of this review was to describe the use of fNIRS to study frontal lobe hemodynamics during cognitive, motor and dual-tasks in older adults. From the 46 included publications, 20 studies used only cognitive tasks, three studies used motor tasks and 23 used dual-tasks. Our findings suggest that fNIRS detects changes in frontal activation in older adults (cognitively healthy and mild cognitive impairment), especially while performing cognitive and dual-tasks. In both the comparison between older and younger adults, and in people with different neurological conditions, compared to healthier controls, the prefrontal cortex seems to experience a higher activation, which could be interpreted in the context of proposed neural inefficiency and limited capacity models. Further research is needed to establish standardized fNIRS protocols, study the cerebral hemodynamic in different neurological and systemic conditions that might influence cortical activation and explore its role in predicting incident health outcomes such as dementia.
Highlights
The worldwide aging of the population makes tackling agingassociated disability an urgent priority
The presence of fear of falling delayed practice-related improvements in prefrontal cortex (PFC) efficiency during DT walking (Holtzer et al, 2019). These findings suggest that Functional Near-Infrared Spectroscopy (fNIRS) can be used to quantify neuroplasticity, monitor improvement in PFC efficiency due to practice and detect the effect of clinically relevant variables such as fear of falling on brain function and efficiency during active walking
Our review supports the use of fNIRS as a neuroimaging technique to study changes in the hemodynamic response in the frontal cortex during cognitively demanding tasks and during active walking under single and DT conditions in older adults
Summary
The worldwide aging of the population makes tackling agingassociated disability an urgent priority. Cognitive impairment and mobility disability are key contributors to dementia and loss of independence in the activities of daily living and have a synergistic effect (Verghese et al, 2014). The integrity of the frontal areas of the brain, the PFC, are critical to preserve cognition and mobility in late life (Beauchet et al, 2016). PFC regions carry out executive functions, i.e., higher order cognitive functions essential to plan and execute complex goal-directed actions, which are key for motor control in older adults (Inzitari et al, 2007). DT performance assessment may help identify older adults at higher risk of incident cognitive decline (Ceïde et al, 2018; Rosso et al, 2019), disability, frailty and mortality (Verghese et al, 2012). Two of the previously described hyphotheses are: the “neural inefficiency hypothesis” (Rypma and D’Esposito, 2000; Holtzer et al, 2009) or “compensation by upregulation” (Cabeza et al, 2018), according to which older adults show increased activity of the same networks recruited by younger counterparts in order to meet behavioral demands, and the “capacity limitation hypothesis” (Cabeza, 2004; Holtzer et al, 2009) which postulates that older adults, while recruiting the same brain networks as young adults, would show a reduced activation compared to their younger counterparts (Holtzer et al, 2009; Stern, 2009)
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