Table 1.
Summary of the characteristics and main findings of the NVC studies included in this review.
| Study ID | Imaging modality | Number of participants | Age of participants (years) | Task activation method | Main findings |
|---|---|---|---|---|---|
| Hyperactivation | |||||
| Jamadar [42] | fMRI | 17 older, 19 younger | Mean ages: 71 and 22 | Working memory, task-switching (four difficulty levels) | Increased activation in the right caudate nucleus older compared to younger adults. At the lower difficulty level, younger adults had increased activation, no differences between groups at an intermediate difficulty and older adults showed increased activity at high difficulty level compared to younger adults. |
| Grinband [34] | BOLD-MRI | 34 older, 55 younger | Mean ages: 65 and 25 | 2 audio-visual tasks | No significant effect of ageing on the time course of the haemodynamic response or the slope of the BOLD vs. stimulus duration relationship |
| Csipo [23] | NIRS | 13 older, 11 younger | Mean ages: 76 and 32 | Finger tapping | Increased haemodynamic response in the contralateral motor and prefrontal cortices in older adults. Delayed and reduced deoxyHb signal, loss of early oxyHb signal |
| Beishon [7] | TCD (MCA) | 25 older, 29 younger | Median ages: 64 and 22 | 8 memory and visuospatial tasks from the Addenbrooke’s cognitive examination-III | Increased peak percentage change in CBFv in older adults in memory (2.17 vs. 8.38%) and visuospatial (5.87 vs. 11.89%, 6.30 vs. 11.30%) tasks |
| Sorond [112] | TCD (ACA and PCA) | 15 older, 14 younger | Mean ages: 74 and 30 | Word-stem completion and visual search tasks | Increased CBFv responses in older compared to younger adults. Loss of regional activation in older group for word-stem completion task |
| Droste [26] | TCD (MCA) | 33 older, 37 younger | Older > 30 years old, younger < 30 years old | 6 tasks encompassing reading, finding nouns, spatial perception, multiplication, facial recognition and assigning dot clusters to a distance scale | Increased CBFv responses to task activation in older adults, but resting CBFv values were lower in older adults at baseline. |
| Neutral activation | |||||
| Stefanidis [114] | TCD (MCA) | 29 older, 29 younger | Older aged over 60, younger aged under 30 | Ten blocks of 40 s of reading | No differences in CBFv responses between older and younger adults (22.9 vs. 21.61%). |
| Madureira [61] | TCD (MCA) | 58 participants across 20 to 80 years | Mean age (total sample): 48 | Working memory task at 1- and 2-back gain | No differences in CBFv responses at 1- or 2-back gain across age strata |
| Hypoactivation | |||||
| Lipecz [57] | Dynamic RVA | 11 older, 18 younger | Mean ages: 75 and 33 | Flicker light stimulation | 51.78% reduction in mean maximal arteriolar dilation in older adults. No differences in venous dilation |
| Kneser [51] | Dynamic RVA | 52 participants across 20–78 years | Total sample range: 20–78 | Flicker light stimulation | Decrease in the arterial regulative amplitude of 45% with age and arterial constriction reduced by 75%. No changes in the venous amplitude |
| West [132] | BOLD-MRI | 173 older, 74 younger | Mean ages: 25 and 64 | Audio-visual task (checkerboard with binaural tone) | Reduced response in older adults with slower time to maximal response and return to baseline in the occipital region |
| Fabiani [29] | BOLD-MRI and NIRS | 44 older, 19 younger | Age ranges: 65–81 and 20–28 | Visual (checkerboard) stimulus | Coupling between oxy- and deoxyHb decreased with age. Haemodynamic responses were reduced in the older group. Greater variability in activation patterns of older adults (oxy-Hb). |
| Kannurpatti [46] | BOLD-MRI | 12 older, 12 younger | Mean ages: 58 and 24 | Cognitive (digit symbol verification) and motor (finger tapping) tasks | Mean activation volume reduced by 45% (motor), 40% (cognitive). Variability in activation volume was higher in older adults for the motor but not a cognitive task. |
| Vermeij [129] | fNIRS | 14 younger, 14 older | Mean ages: 26 and 70 | Working memory (verbal n-back: 0-back, control; 2-back, high working memory load) | Very low-frequency and low-frequency oscillations were reduced in older compared to younger adults during task performance. In younger adults, this increased with cognitive load. |
| Nowak-Flük [76] | TCD (MCA and PCA) | 9 older, 10 younger | Mean ages: 66 and 23 | Visual stimulation (reading) | NVC responses were reduced in older adults at rest (13.9 vs. 23.1%) and during exercise (20.6 vs. 27.4% and 16.6 vs. 24.4%) but not different between rest and exercise. |
| Flük [30] | TCD (MCA and PCA) | 20 older, 10 younger | Mean ages: 64 and 30 | Visual stimulation (checkerboard) | CBFv responses were reduced in the older group but this was not associated with arterial stiffness. |
| Zaletel [138] | TCD (PCA) | 14 older, 26 younger | Mean ages: 70 and 38 | Visual (checkboard) stimulus at 100, 10 and 1% visual contrasts, and visual evoked potentials | Younger adults had higher flow responses (139, 119 and 129% higher at 100, 10 and 1% visual contrasts). NVC index was reduced in older adults. |
| Orlandi [80] | TCD (MCA) | 25 older, 30 younger | Mean ages: 67 and 26 | Simple motor tasks | In older adults, CBFv responses were reduced with less lateralisation, delayed peak response and the return to baseline was increased. |
ACA, anterior cerebral artery; BOLD-MRI, blood oxygen level-dependent magnetic resonance imaging; MCA, middle cerebral artery; NIRS, near-infrared spectroscopy; PCA, posterior cerebral artery; RVA, retinal vessel analysis; TCD, transcranial Doppler ultrasonography