Amount Of Interindividual Variability Research Articles

Inter-subject pattern analysis: A straightforward and powerful scheme for group-level MVPA

Multivariate pattern analysis (MVPA) has become vastly popular for analyzing functional neuroimaging data. At the group level, two main strategies are used in the literature. The standard one is hierarchical, combining the outcomes of within-subject decoding results in a second-level analysis. The alternative one, inter-subject pattern analysis, directly works at the group-level by using, e.g. a leave-one-subject-out cross-validation. This study provides a thorough comparison of these two group-level decoding schemes, using both a large number of artificial datasets where the size of the multivariate effect and the amount of inter-individual variability are parametrically controlled, as well as two real fMRI datasets comprising 15 and 39 subjects, respectively. We show that these two strategies uncover distinct significant regions with partial overlap, and that inter-subject pattern analysis is able to detect smaller effects and to facilitate the interpretation. The core source code and data are openly available, allowing to fully reproduce most of these results.

MR Angiography at 7T to Visualize Cerebrovascular Territories.

There is considerable amount of interindividual variability in the size and location of the vascular territories of the major brain arteries. More data are needed to assess the amount of variability and the possible implications for further research and patient care. Arterial spin labeling (ASL) magnetic resonance imaging has been applied in various forms to facilitate noninvasive imaging of cerebrovascular flow territories, but it requires the definition of the flow territory of interest prior to image acquisition. Assessing the vascular territories of the major brain territories by using ultra-high-field time-of-flight (TOF) magnetic resonance angiography. We have developed an alternative method to ASL by simulating cerebrovascular dye injections. Following bias field normalization and segmentation of the vessels from 7 Tesla TOF imaging, a virtual model of the arterial vessel tree was generated and a simulation of dye dispersion into the brain tissue was performed. The results provided by our method are consistent with the data obtained by autoptic dye injection studies in 23 human beings by van der Zwan in 1993. Further technical improvements in imaging and segmentation techniques will improve the accuracy of the method and will facilitate the delineation of flow territories after image acquisition on even smaller subtrees of the cerebral vasculature.

Dual-task costs in aging are predicted by formal education.

The capacity to manage different concurrent tasks at the same time decays in older adults. There is however a considerable amount of inter-individual variability in this capacity even in healthy aging. The purpose of this empirical study is to investigate which factors help explaining this variability. A dual-task paradigm was administered to 64 older adults and 31 younger controls. In this paradigm, a primary simple response time task had to be carried out either by itself (single-task condition) or while concurrently performing a secondary subtraction task (dual-task condition). Dual-task costs were operationalized by comparing dual-task and single-task conditions. Older adults showed higher dual-task interference than younger controls. Within the older group, the influence of age, general cognitive abilities, performance on the secondary task, and years of formal education was assessed with a multiple regression analysis. The results showed that years of formal education in older adults were the best predictor that significantly explained a portion of the variance in dual-task performance. These findings extend previous literature by showing that formal education provides an important dose of cognitive reserve, which is useful to successfully implement cognitive dual-task management despite aging.

Independent Effect of Self-selected versus Imposed Exercise Intensity on Affect

The affective response to self-selected and imposed exercise intensities of differing physical stimuli has been previously compared in adults and children. PURPOSE: The primary purpose of this investigation was to compare the affective response to self-selected (SS) and imposed (IMP) exercise of the same intensity in young, recreationally active adult males. The secondary purpose was to determine if a significant proportion of subjects self-selected exercise intensity above 50% of oxygen uptake reserve (VO2R). METHODS: 32 males [mean(SD) age 22.3(2.2), VO2PEAK 3.38(0.59)] participated in the investigation. All subjects performed a load-incremented VO2PEAK test and a 20-min, SS exercise trial on a cycle ergometer. One week later, subjects performed the IMP exercise trial. Subjects in the experimental (EXP) group (n=16) were unaware that the IMP intensity was the same as that previously self-selected. These subjects were told the intensity was 'selected by the investigators.' Control (CON) subjects (n=16) were aware that the intensity of the IMP trial was the same as the SS trial. The affective response measured using Feeling Scale ratings (FS-R) was obtained prior to, during, and following the SS and IMP trials. ΔFS-R values, calculated by subtracting FS-R estimated during the SS trial from that of the IMP trial at each time point, were compared between EXP and CON subjects using a mixed-model ANOVA. The proportion of subjects who self-selected intensities above 50% VO2R was tested using a chi-squared analysis. RESULTS: The ANOVA revealed no significant difference between the EXP and CON groups, F(1,30)=0.277, p=0.62. The chi-squared analysis revealed that a significant (p<0.05) proportion of subjects (28 of 33) self-selected exercise intensities above 50% VO2R. CONCLUSIONS: In the current investigation, the affective response to SS and IMP exercise intensities of the same physical stimuli was similar, although there was a considerable amount of inter-individual variability. However, it was found that most subjects self-selected exercise intensities above a level determined by the American College of Sports Medicine to elicit health-fitness benefits. The prescription of SS exercise may be appropriate for young, recreationally active adult males.

A New Technique for Functional Imaging in Songbirds and Beyond

The quantitative study of cerebral hemodynamics requires measurement methods with high spatial and temporal resolution. In the best case, these methods are noninvasive or even contact free. Mottin et al (2010, this issue) propose picosecond optical tomography, or POT, to quantitatively image hemodynamics in a contact-free way. POT relies on white laser light spectral absorption in the near-infrared measured with a streak camera. The tens-of-femtosecond temporal resolution of the streak camera enables depth-specific imaging of oxy- and deoxy-hemoglobin concentration with submillimeter resolution. The authors validate their technique on a songbird model of auditory perception and show results consistent with previous findings that were obtained using functional magnetic resonance imaging (MRI). Furthermore, they shed new light onto brain oxygen recoupling in these tachymetabolic animals, results that would be difficult to obtain with conventional functional MRI. The songbird model is an interesting choice for demonstrating the validity of POT, as songbirds provide a versatile model for studying neuronal plasticity (Brenowitz, 2004). This includes the ability to generate a significant amount of new neurons in adult life (Nottebohm, 2002), as well as the rare trait of vocal learning (Mooney, 2009). Songbirds produce behavioral patterns of high complexity (song) that can be precisely recorded and related to neuronal dynamics from time scales of milliseconds to a time spanning several generations (Hahnloser et al, 2002; Feher et al, 2009). It might be possible that POT adds information to more classical methods of birdsong research based on electrical recordings or functional MRI by virtue of its quantitative nature. For example, could it be used to get a better picture of how the song system works as a network of connected song nuclei by quantitatively analyzing the hemodynamic response dynamics? Besides further applications in songbird research, these advantages could also play out in functional studies of neurovascular plasticity, as has been observed for example after focal cerebral injury (Whitaker et al, 2007), or in neurovascular repair mechanisms after induction of small-scale cortical vascular lesions (Nishimura et al, 2006) that are believed to have a function in aging-related cognitive decline. As they point out at the end of the article, this is a field worth studying for Mottin et al too, by using their technology to investigate a proposed link between brain aging and changes in vascular reactivity found by functional MRI. However, it remains to be seen if POT can compete with the very powerful imaging techniques already used in this field, such as multiphoton microscopy and voltage sensitive dye imaging (Brown et al, 2009). Finally, the authors propose a way to expand POT into a true two-dimensional imaging method (so far it can only image line segments) by sweeping the optical field over the sample. In the long term, functional imaging methods like this could, once developed for human applications, become more relevant clinically (Prakash et al, 2009). As functional MRI maps of the human cortex display a considerable amount of interindividual variability, it is necessary to map, for example, eloquent sensorimotor areas before or during brain tumor surgery. Often, a combination of electrocortical stimulation mapping on the exposed brain and functional MRI is used to identify eloquent sensorimotor areas and thus to reduce surgical risks (Holodny, 2008). It can be envisioned that optical imaging methods based on POT could be used in the operating room to rapidly map individual eloquent cortical areas during surgery.

Human interindividual variability in susceptibility to airborne particles.

Part of the explanation for the persistent epidemiological findings of associations between mortality and morbidity with relatively modest ambient exposures to airborne particles may be that some people are much more susceptible to particle-induced responses than others. This study assembled a database of quantitative observations of interindividual variability in pharmacokinetic and pharmacodynamic parameters likely to affect particle response. The pharmacodynamic responses studied included data drawn from epidemiologic studies of doses of methacholine, flour dust, and other agents that induce acute changes in lung function. In general, the amount of interindividual variability in several of these pharmacodynamic response parameters was greater than the variability in pharmacokinetic (breathing rate, deposition, and clearance) parameters. Quantitatively the results indicated that human interindividual variability of breathing rates and major pharmacokinetic parameters-total deposition and tracheobronchial clearance-were in the region of Log(GSD) = 0.1 to 0.2 (corresponding to geometric standard deviations of 10(.1)-10(.2) or 1.26-1.58). Deposition to the deep lung (alveolar region) appeared to be somewhat more variable: Log(GSD) of about 0.3 (GSD of about 2). Among pharmacodynamic parameters, changes in FEV1 in response to ozone and metabisulfite (an agent that is said to act primarily on neural receptors in the lung) were in the region of Log(GSD) of 0.2 to 0.4. However, similar responses to methacholine, an agent that acts on smooth muscle, seemed to have still more variability (0.4 to somewhat over 1.0, depending on the type of population studied). Similarly high values were suggested for particulate allergens. Central estimates of this kind of variability, and the close correspondence of the data to lognormal distributions, indicate that 99.9th percentile individuals are likely to respond at doses that are 150 to 450-fold less than would be needed in median individuals. It seems plausible that acute responses with this amount of variability could form part of the mechanistic basis for epidemiological observations of enhanced mortality in relation to ambient exposures to fine particles.

Regarding the validity of methods of body composition assessment in young and older men and women

To the Editor: In their recent paper, Clasey and coworkers ([3][1]) compared several different methods of estimating body fat. The authors took as their reference method a 4-compartment model involving the measurement of body density, total body water, and total body bone ash ([5][2]). They then

An oculomotor test to measure alcohol impairment.

Drunk driving continues to be one of the nation's most serious safety problems. On the premise that oculomotor control provides a quantitative measure that is very sensitive to alcohol impairment, an oculomotor test previously developed as a portable hand-held Viewmaster viewer with specially designed grating patterns as images was used to stress the oculomotor system. Test scores decreased with increased alcohol impairment along with a large dependence on individual lateral phoria scores. Unfortunately, there was a large amount of interindividual variability, which may limit use of the test for the population at large unless other individual characteristics are included.