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Statistical Parametric Mapping The Analysis Of Functional Brain Images

Continuous-wave near-infrared spectroscopy and near-infrared imaging enable the measurement of relative concentration changes in oxy- and deoxyhemoglobin and thus hemodynamics and oxygenation. The accuracy of determined changes depends mainly on the modeling of the light transport through the probed tissue. Due to the highly scattering nature of tissue, the light path is longer than the source-detector separation (d). This is incorporated in modeling by multiplying d by a differential pathlength factor (DPF) which depends on several factors such as wavelength, age of the subject, and type of tissue. In the present work, we derive a general DPF equation for the frontal human head, incorporating dependency on wavelength and age, based on published data. We validated the equation using different data sets of experimentally determined DPFs from six independent studies.

https://www.zora.uzh.ch/id/eprint/89593/1/Scholkmann_General_equation_2013_Neo_USZ.pdf

General equation for the differential pathlength factor of the frontal human head depending on wavelength and age

Cerebral blood flow measured by arterial spin labeling MRI at resting state in normal aging and Alzheimer's disease.

High-intensity exercise has recently emerged as a potent alternative to aerobic regimens, with ramifications for health and brain function. As part of this trend, single sessions of intense exercise have been proposed as powerful, noninvasive means for transiently enhancing cognition. However, findings in this field remain mixed, and a thorough synthesis of the evidence is lacking. Here, we synthesized the literature in a meta-analysis of the acute effect of high-intensity exercise on executive function. We included a total of 1,177 participants and 147 effect sizes across 28 studies and found a small facilitating effect (d = 0.24) of high-intensity exercise on executive function. However, this effect was significant only compared with rest (d = 0.34); it was not significant when high-intensity exercise was compared with low-to-moderate intensity exercise (d = 0.07). This suggests that intense and moderate exercise affect executive function in a comparable manner. We tested a number of moderators that together explained a significant proportion of the between-studies variance. Overall, our findings indicate that high-intensity cardiovascular exercise might be a viable alternative for eliciting acute cognitive gains. We discuss the potential of this line of research, identify a number of challenges and limitations it faces, and propose applications to individuals, society, and policies.

The Acute Effect of High-Intensity Exercise on Executive Function: A Meta-Analysis.

The neuroimaging literature on dual-task gait clearly demonstrates increased prefrontal cortex (PFC) involvement when performing a cognitive task while walking. However, findings from direct comparisons of the cerebral oxygenation patterns of younger (YA) and older (OA) adults during dual-task walking are mixed and it is unclear how YA and OA respond to increasing cognitive load (difficulty) while walking. This functional near infra-red (fNIRS) study examined cerebral oxygenation of YA and OA during self-paced dual-task treadmill walking at two different levels of cognitive load (auditory n-back). Changes in accuracy (%) as well as oxygenated (HbO) and deoxygenated (HbR) hemoglobin were examined. For the HbO and HbR measures, eight regions of interest (ROIs) were assessed: the anterior and posterior dorsolateral and ventrolateral PFC (aDLPFC, pDLPFC, aVLPFC, pVLPFC) in each hemisphere. Nineteen YA (M = 21.83 yrs) and 14 OA (M = 66.85 yrs) walked at a self-selected pace while performing auditory 1-back and 2-back tasks. Walking alone (single motor: SM) and performing the cognitive tasks alone (single cognitive: SC) were compared to dual-task walking (DT = SM + SC). In the behavioural data, participants were more accurate in the lowest level of load (1-back) compared to the highest (2-back; p ˂ .001). YA were more accurate than OA overall (p = .009), and particularly in the 2-back task (p = .048). In the fNIRS data, both younger and older adults had task effects (SM < DT) in specific ROIs for ∆HbO (3 YA, 1 OA) and ∆HbR (7 YA, 8 OA). After controlling for walk speed differences, direct comparisons between YA and OA did not reveal significant age differences, but did reveal a difficulty effect in HbO in the left aDLPFC (p = .028) and significant task effects (SM < DT) in HbR for 6 of the 8 ROIs. Findings suggest that YA and OA respond similarly to manipulations of cognitive load when walking on a treadmill at a self-selected pace.

/pdf/comparable-cerebral-oxygenation-patterns-in-younger-and-1qfoxp8orb.pdf

Comparable Cerebral Oxygenation Patterns in Younger and Older Adults during Dual-Task Walking with Increasing Load.

To assess the relationship between exercise intensity, cerebral HbO2 and cognitive performance (Executive and non-Executive) in young adults. We measured reaction time (RT) and accuracy, during a computerized Stroop task, in 19 young adults (7 males and 12 females). Their mean ± SD age, height, body mass and body mass index (BMI) were 24 ± 4 years, 1.67 ± 0.07 m, 72 ± 14 kg and 25 ± 3 kg m−2, respectively. Each subject performed the Stroop task at rest and during cycling at exercise of low intensity [40 % of peak power output (PPO)], moderate intensity (60 % of PPO) and high intensity (85 % of PPO). Cerebral oxygenation was monitored during the resting and exercise conditions over the prefrontal cortex (PFC) using near-infrared spectroscopy (NIRS). High-intensity exercise slowed RT in both the Naming (p = 0.04) and the Executive condition (p = 0.04). The analysis also revealed that high-intensity exercise was associated with a decreased accuracy when compared to low-intensity exercise (p = 0.021). Neuroimaging results confirm a decrease of cerebral oxygenation during high-intensity exercise in comparison to low- (p = 0.004) and moderate-intensity exercise (p = 0.003). Correlations revealed that a lower cerebral HbO2 in the prefrontal cortex was associated with slower RT in the Executive condition only (p = 0.04, g = −0.72). Results of the present study suggest that low to moderate exercise intensity does not alter Executive functioning, but that exercise impairs cognitive functions (Executive and non-Executive) when the physical workload becomes heavy. The cerebral HbO2 correlation suggests that a lower availability of HbO2 was associated with slower RT in the Executive condition only.

The relationship between exercise intensity, cerebral oxygenation and cognitive performance in young adults

Diffuse, optical near infrared imaging is increasingly being used in various neurocognitive contexts where changes in optical signals are interpreted through activation maps. Statistical population comparison of different age or clinical groups rely on the relative homogeneous distribution of measurements across subjects in order to infer changes in brain function. In the context of an increasing use of diffuse optical imaging with older adult populations, changes in tissue properties and anatomy with age adds additional confounds. Few studies investigated these changes with age. Duncan et al. measured the so-called diffusion path length factor (DPF) in a large population but did not explore beyond the age of 51 after which physiological and anatomical changes are expected to occur [Pediatr. Res. 39(5), 889-894 (1996)]. With increasing interest in studying the geriatric population with optical imaging, we studied changes in tissue properties in young and old subjects using both magnetic resonance imaging (MRI)-guided Monte-Carlo simulations and time-domain diffuse optical imaging. Our results, measured in the frontal cortex, show changes in DPF that are smaller than previously measured by Duncan et al. in a younger population. The origin of these changes are studied using simulations and experimental measures.

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-17/issue-5/056002/Changes-in-diffusion-path-length-with-old-age-in-diffuse/10.1117/1.JBO.17.5.056002.pdf

Changes in diffusion path length with old age in diffuse optical tomography.

Like other neuroimaging techniques assessing cerebral blood oxygenation, near-infrared spectroscopy (NIRS) has been applied in many neurocognitive studies. With NIRS, neural activation can be explored indirectly via hemodynamic changes in the imaged region. In studies of aging, changes in baseline physiology and brain anatomy confound NIRS measures seeking to investigate age-related changes in neuronal activity. The field is thus hampered by the complexity of the aging process itself, and statistical inferences from functional data acquired by optical imaging techniques must be interpreted with care. Multimodal integration of NIRS with both structural and baseline physiological assessments is crucial to avoid misinterpreting neuroimaging signals. In this study, a combination of two different optical techniques, anatomical MRI and Arterial Spin Labeling (ASL) was used to investigate age-related changes in activation during a lexical-semantic processing task. Quantitative analysis revealed decreased baseline oxyhemoglobin and cerebral blood flow in the older adults. Using baseline physiology measures as regressors in the investigation of functional concentration changes when doing analyses of variance, we found significant changes in task-induced areas of activity. In the right hemisphere, more significant age-related activity was observed around the junction of the inferior frontal gyrus and inferior precentral sulcus, along with engagement of Wernicke’s area. In the left hemisphere, the degree and extent of frontal activation, including the dorsolateral prefrontal cortex and inferior frontal gyrus, differed between age groups. Measuring background physiological differences and using their values as regressors in statistical analyses allowed a more appropriate, age-corrected understanding of the functional differentiations between age groups. Age-corrected baselines are thus essential to investigate which components of the NIRS signal are altered by aging.

/pdf/an-exploration-of-the-effect-of-hemodynamic-changes-due-to-1ayqftut66.pdf

An Exploration of the Effect of Hemodynamic Changes Due to Normal Aging on the fNIRS Response to Semantic Processing of Words.

Diffuse optical imaging (DOI) of the brain has emerged as a new neuroimaging technique that is seeing growing applications in brain research. The technique’s simplicity, lower cost and applicability to children have contributed to its popularity. However, poor quantification of local hemodynamic changes based on optical signals remains a major hurdle and significant efforts are still being pursued to better understand how to recover accurate images of functional activation, generate statistical maps and recognize the limitations of DOI. In the context of aging, further confounds arise due to anatomical and physiological changes that must be accounted for in the signal modeling. In this work, DOI signals are revisited in this context. In particular we investigate the diffusion path length factor and its modifications with age.

Clément Bonnéry

Papers

The relationship between exercise intensity, cerebral oxygenation and cognitive performance in young adults

Changes in diffusion path length with old age in diffuse optical tomography.

An Exploration of the Effect of Hemodynamic Changes Due to Normal Aging on the fNIRS Response to Semantic Processing of Words.

Diffuse Optical Tomography and Biophysical Modeling of the Aging Brain

An Event-Related fNIRS Approach to the Study of Word Processing in Aging: Preliminary Results Looking at Concreteness