TABLE 2.
Summary of the studies assessing fNIRS measures during motor and/or dual-tasks in older adults.
| First author (Journal, year), Country | Sample size (N) Clinical characteristics of the sample (mean age +SD) NIRS optodes localization | Paradigm description | Main fNIRS results |
| (2A) Motor tasks | |||
| Mahoney (Brain Res., 2016), USA (Mahoney et al., 2016) | N = 269 Parkinsonian syndrome (81.2 ± 5.9); Mild parkinsonian signs (77.5 ± 6.7); healthy adults (74.4 ± 6.1). Prefrontal. |
Task: –Postural control while standing and silently counting for 10 sec. |
⇑: Parkinsonian syndromes: increased prefrontal activation to maintain postural control (compared to the other two groups). |
|
Maidan (Brain Topogr., 2017), Israel (Maidan et al., 2017) |
N = 49 PD without cognitive impairment or freezing of gait (72.8 ± 1). Frontal. |
Task: –Walk with turns: 30-m walk and 180° turn. –Five trials: 20 s of quiet standing between walk and turn. Rest: 20 s before and after each walk (quiet standing). |
⇑: Increased activation during walking and decrease during turns (compared to baseline). ⇑: Older adults with lower gait speed (<1 m/sec): higher activation during turns (compared to older adults with normal gait speed). |
|
Thumm (Gait Posture, 2018), Israel (Thumm et al., 2018) |
N = 20 PD (69.8 ± 6.4). Prefrontal. |
Task: –30-m over-ground vs. treadmill walking. –Five trials (30 s each). Rest: 20 s quiet standing. |
⇓: Lower activation during treadmill walking (compared to over-ground walking). |
| (2B) Dual-tasks | |||
|
Doi (Aging Clin Exp Res., 2013), Japan (Doi et al., 2013) |
N = 16 Older adults with MCI (75.4 ± 7.2). Prefrontal. |
Tasks: –ST: 10-m walk. –DT: 10-m walk + phonetic verbal fluency. –Three trials in each condition (20 s each). Rest: 10 s pre-task and 30 s post-task (standing). |
⇑: Increased prefrontal activation during DT walking compared to ST walking. |
|
Ohsugi (BMC Neurosc., 2013), Japan (Ohsugi et al., 2013) |
N = 35 Healthy older adults (77.9 ± 5.3) vs. young (26 ± 3.6). Prefrontal. |
Tasks: –ST: seated stepping while forward counting from 0. –ST: serial 7-subtraction from 100. –DT: stepping + subtraction. –Each task repeated three times (30 s each). Rest: 30 s (self-paced counting). |
⇑: Higher O2Hb values during DT compared to stepping as ST. ST count showed higher activation compared to stepping. ⇑: Older adults: higher O2Hb levels during DT compared to younger adults. |
|
Beurskens (Int J Physchophysiol., 2014), Germany (Beurskens et al., 2014) |
N = 25 Healthy older adults (71.0 ± 3.8) vs. younger adults (24.5 ± 3.3). Prefrontal. |
Tasks: –ST: treadmill walk. –ST: checking boxes on paper. –ST: reciting alternate alphabet. –DT: walk + check. –DT: walk + alphabet. Each task: 30 s and repeated twice. Rest: seated (duration is not specified). |
⇓: Older adults: lower activation during walk + check compared to ST walk. No significant difference between walk + alphabet vs. walk. Young: no significant difference in activation during ST vs. DT. ⇑: Higher activation in younger adults compared to older adults during visually demanding dual-task (walk + check). |
|
Clark (Front Aging Neurosci., 2015) (Clark et al., 2014) |
N = 16 Older adults with mild mobility difficulties (77.2 ± 5.6). Prefrontal. |
Tasks: –ST: 90-meter walk (5 × 18 m). –Walk + phonetic verbal fluency. –Walk + dimmed light. –Walk + carrying tray. –Walk + 6 obstacles negotiation. –Walk + weighted vest. Rest: 1 min quite standing between tasks. |
⇑: Increased activation during DT walk + verbal fluency, walk + vest, walk + obstacles. Although not significative, there was a trend toward increase during DT walk carrying tray and walk with dimmed light. |
|
Holtzer (Neuroimage, 2015), USA (Holtzer et al., 2015) |
N = 348 Healthy older adults (76.8 ± 6.8). Prefrontal. |
Tasks: –ST: Walk 3 loops on 14-feet walkway. –ST: 30 s reciting alternate alphabet. –DT: Walk + alphabet. Rest: 10 s standing still and counting silently before tasks. |
⇑: Bilateral increases in O2Hb during DT compared to normal walk. In ST walk, after an initial increase, O2Hb levels decrease in the course of the walk. While during the DT walk, O2Hb remains elevated during the task. |
|
Al-Yahya (Neurorehabil Neural Repair, 2016), UK (Al-Yahya et al., 2016) |
N = 19 Chronic stroke (66.2 ± 8.3); healthy controls (56.2 ± 9.5). Prefrontal. |
Tasks: –ST: feet tapping. –ST: backward count. –DT: feet tap + count. Five trials (30 s for each task). Rest: 25–45 s in a pseudo-random order after each task. |
⇑: Higher O2Hb during DT compared to ST in stroke participants compared to healthy controls. |
|
Hernández (J Neurol Sci., 2016), USA (Hernandez et al., 2016) |
N = 16 Multiple Sclerosis (57 ± 5); healthy controls (61 ± 4). Prefrontal. |
Tasks: –ST: Walk 3 loops on walkway. –ST: 30 s reciting alternate alphabet. –DT: Walk + alphabet. Rest: 10 s standing still and counting silently before tasks. |
⇑: Higher O2Hb levels in MS compared to healthy controls in walking tasks. Larger increase in O2Hb from ST walk to DT in MS compared to healthy controls. |
|
∗
Holtzer (Brain Topogr, 2016), USA (Holtzer et al., 2016) |
N = 236 Healthy older adults (75.5 ± 6.5). Prefrontal. |
Tasks: –ST: Walk 3 loops on 14-feet electronic walkway. –ST: Reciting alternate alphabet (30 s). –DT: Walk + alphabet. Rest: 10 s standing still and counting silently before tasks. |
⇑: Normal gait: Higher O2Hb levels in DT compared to ST walk. ⇓: Central NGA: attenuated changes in PFC O2Hb levels from ST to DT compared to peripheral NGA and normal gait group. ⇑: Peripheral NGA showed greatest increase in O2Hb during DT. |
|
Maidan (Neurorehabil Neural Repair, 2016) (Maidan et al., 2016) |
N = 106 PD (71.6 ± 0.9); healthy older adults (70.4 ± 0.9). Prefrontal. |
Tasks: –ST: Walk on 30-m walkway (30 s). –DT: Walk + serial subtractions. –DT: Walk + obstacles. 5 trials each task. Rest: 1 min before whole paradigm starts and 20 s standing before and after tasks. |
⇑: Increased frontal activation during DT walking compared with ST walking in healthy group. ⇓: In PD, HbO2 levels did not increase during DT. ⇑: In PD, HbO2 increased during walk + obstacle compared with ST walking. ⇑: Higher increase in activation during ST walking in PD compared to healthy controls. No significant difference between groups during DT walks. |
|
Nieuwhof (Pilot Feasibility Stud., 2016), Netherlands (Nieuwhof et al., 2016) |
N = 12 Parkinson’s Disease (70.1 ± 5.4). Prefrontal. |
Tasks: –DT: Walk + counting forward. –DT: Walk + serial 3 or 7-substraction. –DT: Walk + reciting digit spans. Five blocks (with 3 tasks each); 40 s each task. Rest: 20 s still-standing before/after task and 1–2 min random rest (while listening to instructions). At least 1 min stand before block. |
⇑ All tasks increased O2Hb during task compared to rest. |
|
∗ Osofundiya (Clin Biomech., 2016), USA (Osofundiya et al., 2016) |
N = 20 Cognitively healthy older adults: obese (80.5 ± 6.8) vs. non-obese (80.6 ± 7.5). Prefrontal |
Tasks: –ST: walk (30 s). –DT: walk + reciting alphabet (30 s). –DT: walk and step on targets on walkway (precision walk). Two blocks: 4 trials (30 s each) per block. Rest: quiet sitting (30 s) before start; 10 s quiet standing between trials; 2 min seating between blocks. |
⇑: Higher PFC activation during DT and precision walk compared to ST walk. ⇑: Obesity associated greater activation in all tasks but specially during precision walking. |
|
Takeuchi (BMC Neurosci., 2016), Japan (Takeuchi et al., 2016) |
N = 31 Healthy older adults (71.7 ± 3.3); young adults (25.9 ± 4.4) Prefrontal. |
Task: –ST: walk for 30 s around a 2.5 m-radius circle –ST: smartphone-based touch game (sitting). Participants instructed to touch in ascending order a set of numbers on screen. –DT: walk + touch. Rest: not described. |
No difference between young vs. old in PFC activation during DT. Less PFC lateralization in older adults to suppress DT cost in gait performance. |
|
Chaparro (J Neuroeng Rehabil., 2017), USA (Chaparro et al., 2017) |
N = 22 Healthy older adults (63.1 ± 4.4); multiple sclerosis (56.2 ± 5.1) Prefrontal. |
Task: –ST: alternate alphabet reciting (standing) –ST: Normal walk –DT: walk while reciting alternate alphabet Walk: 30 s warm-up walk; 30 s test; 15 s deceleration Rest: 10 s before each task (quiet standing). Protocol performed with and without partial body weight support |
⇑: Higher activation during DT compared to normal walk. ⇑: MS older adults: larger increase in O2Hb during all tasks in all conditions compared to healthy older adults (especially during DT without partial body weight support). |
|
Chen (Gait Posture, 2017), USA (Chen et al., 2017) |
N = 90 Healthy older adults (78 ± 15.5). Prefrontal. |
Tasks: –ST: Walk 3 loops on 14ft electronic walkway. –DT: Walk + alternate alphabet reciting. –ST: Walk with obstacle negotiation. –DT: Walk with obstacle + alternate alphabet reciting. Rest: 10 s standing still and counting silently before tasks. |
⇑: Higher activation during DT compared to ST in both normal walk and walk with obstacles. ⇑: Participants with slower gait showed higher increase in O2Hb during walk with obstacles compared to unobstructed walk (relative to participants with normal gait). |
|
∗
Holtzer (Eur J Neurosci., 2017), USA (Holtzer et al., 2017a) |
N = 318 Healthy older adults (76.6 ± 6.7). Prefrontal. |
Tasks: –ST: Walk (3 loops on 14-feet electronic walkway). –ST: Reciting alternate alphabet (30 s). –DT: Walk + alphabet. Rest: 10 s standing still and counting silently before tasks. |
⇓: Higher levels of perceived task-related stress associated attenuation of brain activation from ST to DT. |
|
∗ Holtzer (J Gerontol A Biol Sci Med Sci., 2017), USA (Holtzer et al., 2017b) |
N = 314 Healthy older adults (76.8 ± 6.7). Prefrontal. |
Tasks: –ST: Walk 3 loops on 14-feet electronic walkway. –ST: Reciting alternate alphabet (30 s). –DT: Walk + alphabet. Rest: 10 s standing still and counting silently before tasks. |
⇑: Increased O2Hb levels during DT walking compared with ST walking. ⇓: Higher levels of subjective fatigue attenuated the increase in O2Hb from ST to DT walking. |
|
Mirelman (Brain Cogn., 2017), Israel (Mirelman et al., 2017) |
N = 43. Healthy older adults (69.7 ± 5.8); younger adults (30.9 ± 3.7). Prefrontal. |
Tasks: –ST: Walk on 30-m walkway. –DT: Walk + serial subtraction. –DT: Walk + obstacles. Three loops on walkway for 30 s for each task. Rest: 20 s quiet standing before/after tasks. |
⇑: Older participants increased O2Hb during DT compared to ST walk and during ST walk compared to rest periods. ⇑: Young adults: Activation during DT compared to ST walk. No increase in O2Hb during ST walking (compared to rest). ⇑: Older adults showed higher O2Hb levels in all tasks compared to younger participant. |
|
Rosso (Gait Posture, 2017), USA (Rosso et al., 2017) |
N = 16 Healthy older adults (74 ± 5); younger adults (24 ± 3). Left prefrontal, temporal, and motor. |
Tasks: –ST: Attention task (seated). –ST: Postural control (standing). –DT: Postural control + attention task. Three trials of each task (121 s each). Rest: 30 s sitting or standing before and after each task. |
⇑: Older adults had greater activation of prefrontal and temporal regions compared to younger adults. |
|
∗
Verghese (Neurology, 2017), USA (Verghese et al., 2017) |
N = 166 Healthy older adults (74.9 ± 6.1). Prefrontal. |
Tasks: –ST: Walk 3 loops on 14-feet walkway. –ST: Reciting alternate alphabet (30 s). –DT: Walk + alphabet. Rest: 10 s standing still and counting silently before tasks. |
⇑: DT walk showed higher PFC activation than ST walk. Higher PFC activation levels on fNIRS during DT predicted incident falls. |
|
Mori (Gait Posture, 2018), Japan (Mori et al., 2018) |
N = 28 Post-stroke (>6 months) with hemiparesis (61.1 ± 9.3); healthy controls (66.3 ± 13.3). Prefrontal. |
Tasks: –ST: Serial subtractions of 3 (standing). –DT: Walk around a circle with 2.5 m radius + serial subtractions of 3. 3 trials. Rest: 60 s (repeat sequence of numbers 1–10). |
⇓: Stroke participants: Lower PFC activation during DT compared to healthy participants. |
|
Hawkins (Hum Mov Sci., 2018), USA (Hawkins et al., 2018) |
N = 48 Post-stroke (>4 years) with hemiparesis (58.0 ± 9.3); older adults with mild gait deficits (77.2 ± 5.6); young healthy adults (22.4 ± 3.2). Prefrontal. |
Tasks: –ST: Walk on an 18-m oval-shaped course. –DT: Walk + obstacle negotiation. –DT: Walk + phonetic verbal fluency. Rest: quiet standing (duration not specified). |
⇑: Elderly vs. young: Higher O2Hb increase during normal walk and obstacle negotiation in the early time period. In the late time period, higher PFC activation during normal walk (but not with obstacles). ⇑: Stroke participants: Higher O2Hb increase during normal walk and obstacle negotiation compared to young participants. Greater activation during obstacle negotiation compared to elderly in the late time period. O2Hb increase was highest in the post-stroke group, followed by older and young adults. |
|
∗
Holtzer (Brain Cogn., 2018), USA (Holtzer et al., 2018a) |
N = 315 Healthy old (76.8 ± 6.7). Prefrontal. | Tasks: –ST: Walk 3 loops on 14-feet walkway. –ST: Reciting alternate alphabet (30 s). –DT: Walk + alphabet. Rest: 10 s standing still and counting silently before tasks. |
⇑: Participants without diabetes: increased O2Hb levels during DT compared to ST walk. ⇓: Diabetes: attenuated increase in O2Hb levels from ST walk to DT (compared to non-diabetics). |
|
∗
Lucas (J Gerontol A Biol Sci Med Sci., 2018), USA (Lucas et al., 2018) |
N = 55 Healthy older adults (74.7 ± 4.9). Prefrontal. | Tasks: –ST: Walk 3 loops on 20-feet walkway. –DT: Walk + reciting alternate alphabet. Rest: 10 s standing still and counting silently before tasks. |
⇑: Higher PFC activation during DT compared to ST. ⇑: Poorer white matter integrity associates greater increase in O2Hb levels during DT. |
AD, Alzheimer’s disease; DT, dual-task; fNIRS, Functional Near-Infrared Spectroscopy; MCI, Mild Cognitive Impairment; NGA, Neurological Gait Abnormalities; O2Hb, oxygenated hemoglobin; PD, Parkinson’s disease; PFC, Prefrontal Cortex; ST, single task; SD, Standard Deviation; VF, Verbal Fluency. ∗Articles assessing modulation of health characteristics on brain activation (Table 3).