Using Cognitive-Motor Dual-Tasks and Functional Near-Infrared Spectroscopy to Characterize Older Adults with and without Subjective Cognitive Decline.

BACKGROUND: Subjective cognitive decline (SCD) refers to individuals who report persistent cognitive deficits but perform normally on neuropsychological tests. Performance may be facilitated by increased prefrontal cortex activation, known as neural compensation, and could be used to differentiate between older adults with and without SCD. OBJECTIVE: This cross-sectional pilot study measured changes in the hemodynamic response (ΔHbO2) using functional near-infrared spectroscopy (fNIRS) as well as cognitive and motor performance during fine and gross motor dual-tasks in older adults with and without SCD. METHODS: Twenty older adults over 60 years old with (n = 10) and without (n = 10) SCD were recruited. Two experiments were conducted using 1) gross motor walking and 2) fine motor finger tapping tasks that were paired with an n-back working memory task. Participants also completed neuropsychological assessments and questionnaires on everyday functioning. RESULTS: Repeated measures ANOVAs demonstrated slower response times during dual-task gait compared to the single task (p = 0.032) and in the non-SCD group, slower gait speed was also observed in the dual compared to single task (p = 0.044). Response times during dual-task finger tapping were slower than the single task (p = 0.049) and greater ΔHbO2 was observed overall in the SCD compared to non-SCD group (p = 0.002). CONCLUSIONS: Examining neural and performance outcomes revealed differences between SCD and non-SCD groups and single and dual-tasks. Greater brain activation during dual-task finger tapping may reflect neural compensation, which should be examined in a larger sample and longitudinally to better characterize SCD.

Associations of Multidomain Interventions With Improvements in Cognition in Mild Cognitive Impairment: A Systematic Review and Meta-analysis.

Importance: Older adults with mild cognitive impairment (MCI) have the highest risk of progressing to dementia. Evidence suggests that nonpharmacological, single-domain interventions can prevent or delay progressive declines, but it is unclear whether greater cognitive benefits arise from multidomain interventions. Objective: To determine whether multidomain interventions, composed of 2 or more interventions, are associated with greater improvements in cognition among older adults with MCI than a single intervention on its own. Data Sources: MEDLINE, Embase, PsycInfo, AgeLine, CINAHL, and Cochrane Central Register of Controlled Trials were systematically searched from database inception to December 20, 2021. Study Selection: Included studies contained (1) an MCI diagnosis; (2) nonpharmacological, multidomain interventions that were compared with a single active control; (3) older adults aged 65 years and older; and (4) randomized clinical trials. Data Extraction and Synthesis: Data were screened and extracted by 3 independent reviewers. Following Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines, random-effects meta-analyses were used to calculate effect sizes from the standardized mean difference (SMD) and 95% CIs. Main Outcomes and Measures: Postintervention cognitive test scores in 7 cognitive domains were compared between single-domain and multidomain groups. Exposure to the intervention was analyzed. Results: A total of 28 studies published between 2011 and 2021, including 2711 older adults with MCI, reported greater effect sizes in the multidomain group for global cognition (SMD, 0.41; 95% CI, 0.23-0.59; P < .001), executive function (SMD, 0.20; 95% CI, 0.04-0.36; P = .01), memory (SMD, 0.29; 95% CI, 0.14-0.45; P < .001), and verbal fluency (SMD, 0.30; 95% CI, 0.12-0.49; P = .001). The Mini-Mental State Examination (SMD, 0.40; 95% CI, 0.17-0.64; P < .001), category verbal fluency test (SMD, 0.34; 95% CI, 0.13-0.56; P = .002), Trail Making Test-B (SMD, 0.46; 95% CI, 0.13-0.80; P = .007), and Wechsler Memory Scale-Logical Memory I (SMD, 0.47; 95% CI, 0.15-0.80; P < .001) and II (SMD, 0.26; 95% CI, 0.07-0.45; P < .001) favored the multidomain group. Exposure to the intervention varied between studies: the mean (SD) duration was 71.3 (36.0) minutes for 19.8 (14.6) weeks with sessions taking place 2.5 (1.1) times per week, and all interventions lasted less than 1 year. Conclusions and Relevance: In this study, short-term multidomain interventions (<1 year) were associated with improvements in global cognition, executive function, memory, and verbal fluency compared with single interventions in older adults with MCI.

Effects of Cardiorespiratory Fitness on Cerebral Oxygenation in Healthy Adults: A Systematic Review.

Introduction: Exercise is known to improve cognitive functioning and the cardiorespiratory hypothesis suggests that this is due to the relationship between cardiorespiratory fitness (CRF) level and cerebral oxygenation. The purpose of this systematic review is to consolidate findings from functional near-infrared spectroscopy (fNIRS) studies that examined the effect of CRF level on cerebral oxygenation during exercise and cognitive tasks. Methods: Medline, Embase, SPORTDiscus, and Web of Science were systematically searched. Studies categorizing CRF level using direct or estimated measures of V̇O2max and studies measuring cerebral oxygenation using oxyhemoglobin ([HbO2]) and deoxyhemoglobin ([HHb]) were included. Healthy young, middle-aged, and older adults were included whereas patient populations and people with neurological disorders were excluded. Results: Following PRISMA guidelines, 14 studies were retained following abstract and full-text screening. Cycle ergometer or treadmill tests were used as direct measures of CRF, and one study provided an estimated value using a questionnaire. Seven studies examined the effects of CRF on cerebral oxygenation during exercise and the remaining seven evaluated it during cognitive tasks. Increased [HbO2] in the prefrontal cortex (PFC) was observed during cognitive tasks in higher compared to lower fit individuals. Only one study demonstrated increased [HHb] in the higher fit group. Exercise at submaximal intensities revealed increased [HbO2] in the PFC in higher compared to lower fit groups. Greater PFC [HHb] was also observed in long- vs. short-term trained males but not in females. Primary motor cortex (M1) activation did not differ between groups during a static handgrip test but [HHb] increased beyond maximal intensity in a lower compared to higher fit group. Conclusion: Consistent with the cardiorespiratory hypothesis, higher fit young, middle-aged, and older adults demonstrated increased cerebral oxygenation compared to lower fit groups. Future research should implement randomized controlled trials to evaluate the effectiveness of interventions that improve CRF and cerebral oxygenation longitudinally.

Hemodynamic responses of quiet standing simultaneously performed with different cognitive loads in older adults.

Postural control decrements with advancing age have been largely identified in the literature. Dual-task paradigms have been utilized to increase older adults' stability in order to direct the attention towards the completion of a secondary task, leaving the automatic motor control processes to modulate posture unconstrained. To the extent that older adults allocate greater attentional resources to maintain an upright posture, the present study aimed at replicating St-Amant et al. (2020) protocol to investigate automatic postural control and prefrontal cortex activation in older adults when simultaneously performing quiet standing wtih different attention-demanding cognitive tasks. Nineteen healthy older adults (71.47 ± 6.01 years) were recruited and self-reported no hearing, musculoskeletal and neurological problems. Older adults were required to perform three different cognitive loads while seated (SC), quietly standing on a force platform (SM), and performing both tasks simultaneously (DT). Static center-of-pressure measurements and wavelet discrete transform did not reveal postural automaticity in dual-task conditions. Conversely, sample entropy values were significantly greater when performing n-back compared to all other tasks in the medial-lateral direction, and significantly greater than SM in the anterior-posterior direction. The relative concentration of oxygenated hemoglobin (HbO) of the left hemisphere was significantly greater than the right when performing n-back, and significantly greater within the left hemisphere when performing n-back compared to double-number sequence. Collectively, our results do not support the presence of automatic postural control in dual-task conditions for older adults. The present study highlights the importance of using numerous variables when investigating posture in order to capture its complexity.

An fNIRS Investigation of Discrete and Continuous Cognitive Demands During Dual-Task Walking in Young Adults.

Introduction: Dual-task studies have demonstrated that walking is attention-demanding for younger adults. However, numerous studies have attributed this to task type rather than the amount of required to accomplish the task. This study examined four tasks: two discrete (i.e., short intervals of attention) and two continuous (i.e., sustained attention) to determine whether greater attentional demands result in greater dual-task costs due to an overloaded processing capacity. Methods: Nineteen young adults (21.5 ± 3.6 years, 13 females) completed simple reaction time (SRT) and go/no-go (GNG) discrete cognitive tasks and n-back (NBK) and double number sequence (DNS) continuous cognitive tasks with or without self-paced walking. Prefrontal cerebral hemodynamics were measured using functional near-infrared spectroscopy (fNIRS) and performance was measured using response time, accuracy, and gait speed. Results: Repeated measures ANOVAs revealed decreased accuracy with increasing cognitive demands (p = 0.001) and increased dual-task accuracy costs (p < 0.001). Response times were faster during the single compared to dual-tasks during the SRT (p = 0.005) and NBK (p = 0.004). DNS gait speed was also slower in the dual compared to single task (p < 0.001). Neural findings revealed marginally significant interactions between dual-task walking and walking alone in the DNS (p = 0.06) and dual -task walking compared to the NBK cognitive task alone (p = 0.05). Conclusion: Neural findings suggest a trend towards increased PFC activation during continuous tasks. Cognitive and motor measures revealed worse performance during the discrete compared to continuous tasks. Future studies should consider examining different attentional demands of motor tasks.

Hemodynamic and behavioral changes in older adults during cognitively demanding dual tasks.

INTRODUCTION: Executive functions play a fundamental role in walking by integrating information from cognitive-motor pathways. Subtle changes in brain and behavior may help identify older adults who are more susceptible to executive function deficits with advancing age due to prefrontal cortex deterioration. This study aims to examine how older adults mitigate executive demands while walking during cognitively demanding tasks. METHODS: Twenty healthy older adults (M = 71.8 years, SD = 6.4) performed simple reaction time (SRT), go/no-go (GNG), n-back (NBK), and double number sequence (DNS) cognitive tasks of increasing difficulty while walking (i.e., dual task). Functional near infra-red spectroscopy (fNIRS) was used to measure the hemodynamic response (i.e., oxy- [HbO2] and deoxyhemoglobin [HbR]) changes in the prefrontal cortex (PFC) during dual and single tasks (i.e., walking alone). In addition, performance was measured using gait speed (m/s), response time (s), and accuracy (% correct). RESULTS: Using repeated measures ANOVAs, neural findings demonstrated a main effect of task such that ∆HbO2 (p = .047) and ∆HbR (p = .040) decreased between single and dual tasks. An interaction between task and cognitive difficulty (p = .014) revealed that gait speed decreased in the DNS between single and dual tasks. A main effect of task in response time indicated that the SRT response time was faster than all other difficulty levels (p < .001). Accuracy performance declined between single and dual tasks (p = .028) and across difficulty levels (p < .001) but was not significantly different between the NBK and DNS. CONCLUSION: Findings suggest that a healthy older adult sample might mitigate executive demands using an automatic locomotor control strategy such that shifting conscious attention away from walking during the dual tasks resulted in decreased ∆HbO2 and ∆HbR. However, decreased prefrontal activation was inefficient at maintaining response time and accuracy performance and may be differently affected by increasing cognitive demands.

Prefrontal Cortex Involvement during Dual-Task Stair Climbing in Healthy Older Adults: An fNIRS Study.

Executive function and motor control deficits adversely affect gait performance with age, but the neural correlates underlying this interaction during stair climbing remains unclear. Twenty older adults (72.7 ± 6.9 years) completed single tasks: standing and responding to a response time task (SC), ascending or descending stairs (SMup, SMdown); and a dual-task: responding while ascending or descending stairs (DTup, DTdown). Prefrontal hemodynamic response changes (∆HbO2, ∆HbR) were examined using functional near-infrared spectroscopy (fNIRS), gait speed was measured using in-shoe smart insoles, and vocal response time and accuracy were recorded. Findings revealed increased ∆HbO2 (p = 0.020) and slower response times (p < 0.001) during dual- versus single tasks. ∆HbR (p = 0.549), accuracy (p = 0.135) and gait speed (p = 0.475) were not significantly different between tasks or stair climbing conditions. ∆HbO2 and response time findings suggest that executive processes are less efficient during dual-tasks. These findings, in addition to gait speed and accuracy maintenance, may provide insights into the neural changes that precede performance declines. To capture the subtle differences between stair ascent and descent and extend our understanding of the neural correlates of stair climbing in older adults, future studies should examine more difficult cognitive tasks.