Near infrared (NIR) light has been widely used for measuring changes in hemoglobin concentration ... more Near infrared (NIR) light has been widely used for measuring changes in hemoglobin concentration in the human brain (functional NIR spectroscopy, fNIRS). fNIRS is based on the differential measurement and estimation of absorption perturbations, which, in turn, are based on correctly estimating the absolute parameters of light propagation. To do so, it is essential to accurately characterize the baseline optical properties of tissue (absorption and reduced scattering coefficients). However, because of the diffusive properties of the medium, separate determination of absorption and scattering across the head is challenging. The effective attenuation coefficient (EAC), which is proportional to the geometric mean of absorption and reduced scattering coefficients, can be estimated in a simpler fashion by multidistance light decay measurements. EAC mapping could be of interest for the scientific community because of its absolute information content, and because light propagation is govern...
Cognitive declines, especially in fluid, online processing, are often associated with normal agin... more Cognitive declines, especially in fluid, online processing, are often associated with normal aging. However, some of these changes are known to be ameliorated through aerobic exercise interventions. Here we hypothesize that some of these agerelated changes may be related to changes in cerebrovascular health in the brain. Increased cardiorespiratory fitness (CRF) may maintain or improve baseline oxygenation and perfusion conditions in the brain. Additionally, cognitive function may be supported by improved vascular reactivity to metabolic needs in neural tissue. Arterial spin labelling (ASL), a magnetic resonance imaging method, can be used to measure perfusion directly, so that we may more closely examine the relationship between fitness, cerebral blood flow (CBF), and cognition in the normal aging brain. This project was supported by a grant NIH 1 RC1 AG035927 Z ARRA to Monica Fabiani and an NSF IGERT fellowship (0903622) to B. Zimmerman. CBF measurement: An arterial spin labeling (ASL) technique was used to measure CBF from six imaging slices passing through the lateral ventricles and covering part of the frontal cortical areas.
Recent studies suggest that cardiorespiratory fitness (CRF) mitigates the brain's atrophy typical... more Recent studies suggest that cardiorespiratory fitness (CRF) mitigates the brain's atrophy typically associated with aging, via a variety of beneficial mechanisms. One could argue that if CRF is generally counteracting the negative effects of aging, the same regions that display the greatest age-related volumetric loss should also show the largest beneficial effects of fitness. To test this hypothesis we examined structural MRI data from 54 healthy older adults (ages 55-87), to determine the overlap, across brain regions, of the profiles of age and fitness effects. Results showed that lower fitness and older age are associated with atrophy in several brain regions, replicating past studies. However, when the profiles of age and fitness effects were compared using a number of statistical approaches, the effects were not entirely overlapping. Interestingly, some of the regions that were most influenced by age were among those not influenced by fitness. Presumably, the age-related atrophy occurring in these regions is due to factors that are more impervious to the beneficial effects of fitness. Possible mechanisms supporting regional heterogeneity may include differential involvement in motor function, the presence of adult neurogenesis, and differential sensitivity to cerebrovascular, neurotrophic and metabolic factors.
Recent studies suggest that cardiorespiratory fitness (CRF) mitigates the brain's atrophy typical... more Recent studies suggest that cardiorespiratory fitness (CRF) mitigates the brain's atrophy typically associated with aging, via a variety of beneficial mechanisms. One could argue that if CRF is generally counteracting the negative effects of aging, the same regions that display the greatest age-related volumetric loss should also show the largest beneficial effects of fitness. To test this hypothesis we examined structural MRI data from 54 healthy older adults (ages 55-87), to determine the overlap, across brain regions, of the profiles of age and fitness effects. Results showed that lower fitness and older age are associated with atrophy in several brain regions, replicating past studies. However, when the profiles of age and fitness effects were compared using a number of statistical approaches, the effects were not entirely overlapping. Interestingly, some of the regions that were most influenced by age were among those not influenced by fitness. Presumably, the age-related atrophy occurring in these regions is due to factors that are more impervious to the beneficial effects of fitness. Possible mechanisms supporting regional heterogeneity may include differential involvement in motor function, the presence of adult neurogenesis, and differential sensitivity to cerebrovascular, neurotrophic and metabolic factors.
The brain's vasculature is likely to be subjected to the same age-related physiological and anato... more The brain's vasculature is likely to be subjected to the same age-related physiological and anatomical changes affecting the rest of the cardiovascular system. Since aerobic fitness is known to alleviate both cognitive and volumetric losses in the brain, it is important to investigate some of the possible mechanisms underlying these beneficial changes.
Cerebrovascular support is crucial for healthy cognitive and brain aging. Arterial stiffening is ... more Cerebrovascular support is crucial for healthy cognitive and brain aging. Arterial stiffening is a cause of reduced brain blood flow, a predictor of cognitive decline, and a risk factor for cerebrovascular accidents and Alzheimer's disease. Arterial health is influenced by lifestyle factors, such as cardiorespiratory fitness (CRF). We investigated new noninvasive optical measures of cerebrovascular health, which provide estimates of arterial pulse parameters (pulse pressure, transit time, and compliance/elasticity) within specific cerebral arteries and cortical regions, and low-resolution maps of large superficial cerebral arteries. We studied naturally occurring variability in these parameters in adults (aged 55-87), and found that these indices of cerebrovascular health are negatively correlated with age and positively with CRF and gray and white matter volumes. Further, regional pulse transit time predicts specific neuropsychological performance.
Abstract: Advancing age is associated with a decline in physical and cognitive abilities. Multipl... more Abstract: Advancing age is associated with a decline in physical and cognitive abilities. Multiple theories have been proposed to account for the psychological impairments seen in older age. These include changes in sensory acuity, general slowing of the nervous system, declines in working memory capacity, and a loss of inhibitory control. Although not inherently incompatible, each of the theories provides a unique interpretation of the observed pattern of psychological and neuronal data.
Neuroimaging data emphasize that older adults often show greater extent of brain activation than ... more Neuroimaging data emphasize that older adults often show greater extent of brain activation than younger adults for similar objective levels of difficulty. A possible interpretation of this finding is that older adults need to recruit neuronal resources at lower loads than younger adults, leaving no resources for higher loads, and thus leading to performance decrements [Compensation-Related Utilization of Neural Circuits Hypothesis; eg, Reuter-Lorenz, PA, & Cappell, KA Neurocognitive aging and the compensation hypothesis.
Neurovascular coupling estimated in young and old adults varying in fitness level.Measurements in... more Neurovascular coupling estimated in young and old adults varying in fitness level.Measurements include neuronal (ERPs, EROS) and hemodynamic (fMRI, NIRS) methods.Non-linear relationship was found between neuronal and hemodynamic measures.Oxy-hemoglobin concentration changes were reduced in low-fit older adults.Brain aging is characterized by changes in both hemodynamic and neuronal responses, which may be influenced by the cardiorespiratory fitness of the individual. To investigate the relationship between neuronal and hemodynamic changes, we studied the brain activity elicited by visual stimulation (checkerboard reversals at different frequencies) in younger adults and in older adults varying in physical fitness. Four functional brain measures were used to compare neuronal and hemodynamic responses obtained from BA17: two reflecting neuronal activity (the event-related optical signal, EROS, and the C1 response of the ERP), and two reflecting functional hemodynamic changes (functional magnetic resonance imaging, fMRI, and near-infrared spectroscopy, NIRS). The results indicated that both younger and older adults exhibited a quadratic relationship between neuronal and hemodynamic effects, with reduced increases of the hemodynamic response at high levels of neuronal activity. Although older adults showed reduced activation, similar neurovascular coupling functions were observed in the two age groups when fMRI and deoxy-hemoglobin measures were used. However, the coupling between oxy- and deoxy-hemoglobin changes decreased with age and increased with increasing fitness. These data indicate that departures from linearity in neurovascular coupling may be present when using hemodynamic measures to study neuronal function.
Previous studies indicate that physical fitness plays a protective role against age-related cogni... more Previous studies indicate that physical fitness plays a protective role against age-related cognitive decline (e.g., Colcombe & Kramer, 2003). Using event-related potentials (ERPs), we investigated age-related cognitive decline in working memory processing and whether physical fitness positively influences working memory capacity in older adults. Data from 13 younger and 25 older adults (tested for their physical fitness) were analyzed. The participants performed a modified Sternberg memory search task while ERPs were recorded. The memory set was presented in upper-case letters, with a memory set size varying from 2 to 6. A lower-case probe letter following the memory set required a positive ("old") or negative ("new") response. Behavioral data showed age-related but not fitness-related differences. The ERPs, elicited by the memory set, showed (a) an age effect in the posterior P1 component, and (b) age and fitness effects in the frontal negativity. These results...
The event-related optical signal (EROS) has been recently proposed as a method for studying nonin... more The event-related optical signal (EROS) has been recently proposed as a method for studying noninvasively the time course of activity in localized cortical areas (G. Gratton and M. Fabiani, 1998, Psychonomic Bull. Rev. 5: 535-563). Previous data have shown that EROS has very good temporal resolution and can provide detailed surface activity maps. In the present study we investigated whether the depth of the active area can also be estimated. Nine subjects were run in a study in which the eccentricity of the visual stimuli was varied, and EROS was recorded from medial occipital areas using multiple source-detector distances. Seven of the same subjects were also run through a functional magnetic resonance imaging (fMRI) study using the same protocol. The fMRI data indicated that the depth from the head surface to the cortical area activated increased systematically with the eccentricity of the visual stimuli. The EROS recording indicated a response with a latency of 60-80 ms from stimulation. This response varied systematically with eccentricity, so that the greater the eccentricity of the stimuli, the longer the source-detector distance (and thus the depth) at which the EROS effect was observed. The depth of the brain area generating the EROS effect was estimated using a simple algorithm derived from phantom studies on homogeneous media. The average depth estimates for each eccentricity condition obtained with EROS corresponded with those obtained with fMRI, with discrepancies of less than 1 mm. These data demonstrate that multiple source-detector distances can be used to estimate the depth of the cortical areas responsible for the EROS effects.
Recent theories about human brain function emphasize the need for imaging methods that allow the ... more Recent theories about human brain function emphasize the need for imaging methods that allow the study of dynamic interactions among different structures. In this paper, we report on a new technique, based on the measurement of parameters of migration of near-infrared photons, that yields functional images of the human occipital cortex, combining a spatial resolution of 0.5 cm and a temporal resolution of 50 ms. This technique appears to be suitable for studying the dynamics of cortical activation.
Older adults often encounter difficulties in switching between tasks, perhaps because of age-rela... more Older adults often encounter difficulties in switching between tasks, perhaps because of age-related decreases in executive function. Executive function may largely depend on connections between brain areas—connections that may become structurally and functionally weaker in aging. Here we investigated functional and structural age-related changes in switching between a spatial and a verbal task. These tasks were chosen because they are expected to differentially use the two hemispheres.
Brief nontonal sounds are used in electrophysiology in the novelty oddball paradigm. These sounds... more Brief nontonal sounds are used in electrophysiology in the novelty oddball paradigm. These sounds vary in the brain activity they elicit and in the degree to which they can be identified, named, and remembered. Because ease of sound identification may influence sound processing, naming and conceptual norms were determined for 100 sounds for 77 young adults (Experiment 1). Naming ability decreases in normal and pathological aging. Therefore, norms were also derived for older adults (Experiment 2) and for probable Alzheimer's disease patients (Experiment 3). With respect to the young adults, perseverative naming behavior increased in these groups, and sound and picture naming performance were correlated. In Experiment 4, the sound-naming performance of children aged 5-6, 9-11, and 14-16 years was compared. Name and conceptual agreements improved with age, whereas perseverative behavior decreased. These normative data should be useful in guiding sound selection in future studies and help clarify the relationships between sound naming and other variables, including direct and indirect memory performance.
Near infrared (NIR) light has been widely used for measuring changes in hemoglobin concentration ... more Near infrared (NIR) light has been widely used for measuring changes in hemoglobin concentration in the human brain (functional NIR spectroscopy, fNIRS). fNIRS is based on the differential measurement and estimation of absorption perturbations, which, in turn, are based on correctly estimating the absolute parameters of light propagation. To do so, it is essential to accurately characterize the baseline optical properties of tissue (absorption and reduced scattering coefficients). However, because of the diffusive properties of the medium, separate determination of absorption and scattering across the head is challenging. The effective attenuation coefficient (EAC), which is proportional to the geometric mean of absorption and reduced scattering coefficients, can be estimated in a simpler fashion by multidistance light decay measurements. EAC mapping could be of interest for the scientific community because of its absolute information content, and because light propagation is govern...
Cognitive declines, especially in fluid, online processing, are often associated with normal agin... more Cognitive declines, especially in fluid, online processing, are often associated with normal aging. However, some of these changes are known to be ameliorated through aerobic exercise interventions. Here we hypothesize that some of these agerelated changes may be related to changes in cerebrovascular health in the brain. Increased cardiorespiratory fitness (CRF) may maintain or improve baseline oxygenation and perfusion conditions in the brain. Additionally, cognitive function may be supported by improved vascular reactivity to metabolic needs in neural tissue. Arterial spin labelling (ASL), a magnetic resonance imaging method, can be used to measure perfusion directly, so that we may more closely examine the relationship between fitness, cerebral blood flow (CBF), and cognition in the normal aging brain. This project was supported by a grant NIH 1 RC1 AG035927 Z ARRA to Monica Fabiani and an NSF IGERT fellowship (0903622) to B. Zimmerman. CBF measurement: An arterial spin labeling (ASL) technique was used to measure CBF from six imaging slices passing through the lateral ventricles and covering part of the frontal cortical areas.
Recent studies suggest that cardiorespiratory fitness (CRF) mitigates the brain's atrophy typical... more Recent studies suggest that cardiorespiratory fitness (CRF) mitigates the brain's atrophy typically associated with aging, via a variety of beneficial mechanisms. One could argue that if CRF is generally counteracting the negative effects of aging, the same regions that display the greatest age-related volumetric loss should also show the largest beneficial effects of fitness. To test this hypothesis we examined structural MRI data from 54 healthy older adults (ages 55-87), to determine the overlap, across brain regions, of the profiles of age and fitness effects. Results showed that lower fitness and older age are associated with atrophy in several brain regions, replicating past studies. However, when the profiles of age and fitness effects were compared using a number of statistical approaches, the effects were not entirely overlapping. Interestingly, some of the regions that were most influenced by age were among those not influenced by fitness. Presumably, the age-related atrophy occurring in these regions is due to factors that are more impervious to the beneficial effects of fitness. Possible mechanisms supporting regional heterogeneity may include differential involvement in motor function, the presence of adult neurogenesis, and differential sensitivity to cerebrovascular, neurotrophic and metabolic factors.
Recent studies suggest that cardiorespiratory fitness (CRF) mitigates the brain's atrophy typical... more Recent studies suggest that cardiorespiratory fitness (CRF) mitigates the brain's atrophy typically associated with aging, via a variety of beneficial mechanisms. One could argue that if CRF is generally counteracting the negative effects of aging, the same regions that display the greatest age-related volumetric loss should also show the largest beneficial effects of fitness. To test this hypothesis we examined structural MRI data from 54 healthy older adults (ages 55-87), to determine the overlap, across brain regions, of the profiles of age and fitness effects. Results showed that lower fitness and older age are associated with atrophy in several brain regions, replicating past studies. However, when the profiles of age and fitness effects were compared using a number of statistical approaches, the effects were not entirely overlapping. Interestingly, some of the regions that were most influenced by age were among those not influenced by fitness. Presumably, the age-related atrophy occurring in these regions is due to factors that are more impervious to the beneficial effects of fitness. Possible mechanisms supporting regional heterogeneity may include differential involvement in motor function, the presence of adult neurogenesis, and differential sensitivity to cerebrovascular, neurotrophic and metabolic factors.
The brain's vasculature is likely to be subjected to the same age-related physiological and anato... more The brain's vasculature is likely to be subjected to the same age-related physiological and anatomical changes affecting the rest of the cardiovascular system. Since aerobic fitness is known to alleviate both cognitive and volumetric losses in the brain, it is important to investigate some of the possible mechanisms underlying these beneficial changes.
Cerebrovascular support is crucial for healthy cognitive and brain aging. Arterial stiffening is ... more Cerebrovascular support is crucial for healthy cognitive and brain aging. Arterial stiffening is a cause of reduced brain blood flow, a predictor of cognitive decline, and a risk factor for cerebrovascular accidents and Alzheimer's disease. Arterial health is influenced by lifestyle factors, such as cardiorespiratory fitness (CRF). We investigated new noninvasive optical measures of cerebrovascular health, which provide estimates of arterial pulse parameters (pulse pressure, transit time, and compliance/elasticity) within specific cerebral arteries and cortical regions, and low-resolution maps of large superficial cerebral arteries. We studied naturally occurring variability in these parameters in adults (aged 55-87), and found that these indices of cerebrovascular health are negatively correlated with age and positively with CRF and gray and white matter volumes. Further, regional pulse transit time predicts specific neuropsychological performance.
Abstract: Advancing age is associated with a decline in physical and cognitive abilities. Multipl... more Abstract: Advancing age is associated with a decline in physical and cognitive abilities. Multiple theories have been proposed to account for the psychological impairments seen in older age. These include changes in sensory acuity, general slowing of the nervous system, declines in working memory capacity, and a loss of inhibitory control. Although not inherently incompatible, each of the theories provides a unique interpretation of the observed pattern of psychological and neuronal data.
Neuroimaging data emphasize that older adults often show greater extent of brain activation than ... more Neuroimaging data emphasize that older adults often show greater extent of brain activation than younger adults for similar objective levels of difficulty. A possible interpretation of this finding is that older adults need to recruit neuronal resources at lower loads than younger adults, leaving no resources for higher loads, and thus leading to performance decrements [Compensation-Related Utilization of Neural Circuits Hypothesis; eg, Reuter-Lorenz, PA, & Cappell, KA Neurocognitive aging and the compensation hypothesis.
Neurovascular coupling estimated in young and old adults varying in fitness level.Measurements in... more Neurovascular coupling estimated in young and old adults varying in fitness level.Measurements include neuronal (ERPs, EROS) and hemodynamic (fMRI, NIRS) methods.Non-linear relationship was found between neuronal and hemodynamic measures.Oxy-hemoglobin concentration changes were reduced in low-fit older adults.Brain aging is characterized by changes in both hemodynamic and neuronal responses, which may be influenced by the cardiorespiratory fitness of the individual. To investigate the relationship between neuronal and hemodynamic changes, we studied the brain activity elicited by visual stimulation (checkerboard reversals at different frequencies) in younger adults and in older adults varying in physical fitness. Four functional brain measures were used to compare neuronal and hemodynamic responses obtained from BA17: two reflecting neuronal activity (the event-related optical signal, EROS, and the C1 response of the ERP), and two reflecting functional hemodynamic changes (functional magnetic resonance imaging, fMRI, and near-infrared spectroscopy, NIRS). The results indicated that both younger and older adults exhibited a quadratic relationship between neuronal and hemodynamic effects, with reduced increases of the hemodynamic response at high levels of neuronal activity. Although older adults showed reduced activation, similar neurovascular coupling functions were observed in the two age groups when fMRI and deoxy-hemoglobin measures were used. However, the coupling between oxy- and deoxy-hemoglobin changes decreased with age and increased with increasing fitness. These data indicate that departures from linearity in neurovascular coupling may be present when using hemodynamic measures to study neuronal function.
Previous studies indicate that physical fitness plays a protective role against age-related cogni... more Previous studies indicate that physical fitness plays a protective role against age-related cognitive decline (e.g., Colcombe & Kramer, 2003). Using event-related potentials (ERPs), we investigated age-related cognitive decline in working memory processing and whether physical fitness positively influences working memory capacity in older adults. Data from 13 younger and 25 older adults (tested for their physical fitness) were analyzed. The participants performed a modified Sternberg memory search task while ERPs were recorded. The memory set was presented in upper-case letters, with a memory set size varying from 2 to 6. A lower-case probe letter following the memory set required a positive ("old") or negative ("new") response. Behavioral data showed age-related but not fitness-related differences. The ERPs, elicited by the memory set, showed (a) an age effect in the posterior P1 component, and (b) age and fitness effects in the frontal negativity. These results...
The event-related optical signal (EROS) has been recently proposed as a method for studying nonin... more The event-related optical signal (EROS) has been recently proposed as a method for studying noninvasively the time course of activity in localized cortical areas (G. Gratton and M. Fabiani, 1998, Psychonomic Bull. Rev. 5: 535-563). Previous data have shown that EROS has very good temporal resolution and can provide detailed surface activity maps. In the present study we investigated whether the depth of the active area can also be estimated. Nine subjects were run in a study in which the eccentricity of the visual stimuli was varied, and EROS was recorded from medial occipital areas using multiple source-detector distances. Seven of the same subjects were also run through a functional magnetic resonance imaging (fMRI) study using the same protocol. The fMRI data indicated that the depth from the head surface to the cortical area activated increased systematically with the eccentricity of the visual stimuli. The EROS recording indicated a response with a latency of 60-80 ms from stimulation. This response varied systematically with eccentricity, so that the greater the eccentricity of the stimuli, the longer the source-detector distance (and thus the depth) at which the EROS effect was observed. The depth of the brain area generating the EROS effect was estimated using a simple algorithm derived from phantom studies on homogeneous media. The average depth estimates for each eccentricity condition obtained with EROS corresponded with those obtained with fMRI, with discrepancies of less than 1 mm. These data demonstrate that multiple source-detector distances can be used to estimate the depth of the cortical areas responsible for the EROS effects.
Recent theories about human brain function emphasize the need for imaging methods that allow the ... more Recent theories about human brain function emphasize the need for imaging methods that allow the study of dynamic interactions among different structures. In this paper, we report on a new technique, based on the measurement of parameters of migration of near-infrared photons, that yields functional images of the human occipital cortex, combining a spatial resolution of 0.5 cm and a temporal resolution of 50 ms. This technique appears to be suitable for studying the dynamics of cortical activation.
Older adults often encounter difficulties in switching between tasks, perhaps because of age-rela... more Older adults often encounter difficulties in switching between tasks, perhaps because of age-related decreases in executive function. Executive function may largely depend on connections between brain areas—connections that may become structurally and functionally weaker in aging. Here we investigated functional and structural age-related changes in switching between a spatial and a verbal task. These tasks were chosen because they are expected to differentially use the two hemispheres.
Brief nontonal sounds are used in electrophysiology in the novelty oddball paradigm. These sounds... more Brief nontonal sounds are used in electrophysiology in the novelty oddball paradigm. These sounds vary in the brain activity they elicit and in the degree to which they can be identified, named, and remembered. Because ease of sound identification may influence sound processing, naming and conceptual norms were determined for 100 sounds for 77 young adults (Experiment 1). Naming ability decreases in normal and pathological aging. Therefore, norms were also derived for older adults (Experiment 2) and for probable Alzheimer's disease patients (Experiment 3). With respect to the young adults, perseverative naming behavior increased in these groups, and sound and picture naming performance were correlated. In Experiment 4, the sound-naming performance of children aged 5-6, 9-11, and 14-16 years was compared. Name and conceptual agreements improved with age, whereas perseverative behavior decreased. These normative data should be useful in guiding sound selection in future studies and help clarify the relationships between sound naming and other variables, including direct and indirect memory performance.
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Papers by Monica Fabiani