Journal

Volume 12, Issue 2 (June 30, 2011)

5 articles

• Editorial (for Special Issue, Vol 12-2)
  by Danny J. J. Wang & Hengyi Rao
  J. CS. 2011, 12(2), 127-128;
  Abstract Over 100 years ago, William James (1890) first suggested that “blood very likely may rush to each region of the cortex according as it is most active.” About 80 years ago, John Fulton (1928) presented the first evidence of an association of blood flow and cognition, describing the case of a patient ... [Read more].
  Abstract Over 100 years ago, William James (1890) first suggested that “blood very likely may rush to each region of the cortex according as it is most active.” About 80 years ago, John Fulton (1928) presented the first evidence of an association of blood flow and cognition, describing the case of a patient with an arteriovenous malformation (AVM) in the occipital cortex who underwent an unsuccessful surgical removal of the AVM. The bruit of blood flow could be heard through the bony defect resulting from the surgery and was found to be correlated with the patient’s mental activity. These suggestions and empirical observations remained intriguing but inconclusive until the introduction of modern neuroimaging tools for measuring regional cerebral blood flow (rCBF), such as Single-Photon Emission Computed Tomography (SPECT), Positron Emission Tomography (PET), and more recently Magnetic Resonance Imaging (MRI). Compared to SPECT and PET, which rely on radioactive tracers, MRI is noninvasive, more economical and widely available. During the past two decades, functional MRI (fMRI) based on blood-oxygen level dependent (BOLD) contrast has revolutionized the field of functional neuroimaging.Arterial spin labeling (ASL) perfusion MRI was first introduced by Detre et al. (1992), one year after the seminal BOLD fMRI papers by Kwong et al. (1991) and Ogawa et al. (1991) published in PNAS. Since their advent, the development of ASL and BOLD fMRI for neuroscientific applications has been analogous to the story of the tortoise and the hare. BOLD is stronger (higher sensitivity), faster (higher temporal resolution) yet unstable in certain aspects (baseline drift effects, field inhomogeneity effects). ASL is slower but more persistent and reproducible (with absolute quantification and reduced sensitivity to drift and field inhomogeneity effects). The past two decades have seen a steady increase of publications using ASL to study brain function, partly owing to continuous innovations of MR technologies, which have improved the sensitivity and reliability of ASL. One of the key features of ASL is its capability for absolute rCBF quantification, which greatly facilitates comparisons of imaging results across age groups and between patient and control groups. In this special issue, Kilroy et al. and Hu et al. apply ASL in typically developing and aging populations respectively. They also compare CBF results with analysis of regional cortical volume in order to tease apart the unique changes in brain function and structure. Because of absolute quantification, ASL based fMRI results in clinical populations can be interpreted more accurately than those of BOLD fMRI. As proof of this, Zou et al. apply ASL to systematically study the load effect in N-back working memory tasks. Their results demonstrate both linear and non-linear relationships (quadratic and cubic) between CBF changes and working memory load, laying the foundation for future applications in neuropsychiatric disorders. Finally, resting rCBF may serve as a surrogate of resting brain function based on a phenomenon termed neurovascular coupling. In this special issue, Kilroy et al. and Gillihan et al. investigate the correlation between resting CBF and IQ in typically developing children, and the correlation between resting CBF and weather-related mood variations in healthy adults, respectively.Although the four papers included in this volume do not cover the entire spectrum of topics related to ASL, we hope they will showcase the potential and promise that ASL brings to the field of cognitive neuroscience. As resting state BOLD fMRI and associated connectivity analysis have become a new standard in the field, one underexploited feature of ASL is its temporal dynamics. We do hope future studies will address this important issue and that ASL may eventually surpass BOLD fMRI for neuroscientific applications, in keeping with the tale of the tortoise and the hare.  [Collapse]
• Quantification of Load Dependent Brain Activity in Parametric N-Back Working Memory Tasks using Pseudo-continuous Arterial Spin
  by Qihong Zou, Hong Gu, Danny J. J. Wang, Jia-Hong Gao, & Yihong Yang
  J. CS. 2011, 12(2), 129-149;
  Abstract Brain activation and deactivation induced by N-back working memory tasks and their load effects have been extensively investigated using positron emission tomography (PET) and blood-oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI). However, the underlying mechanisms of... [Read more].
  Abstract Brain activation and deactivation induced by N-back working memory tasks and their load effects have been extensively investigated using positron emission tomography (PET) and blood-oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI). However, the underlying mechanisms of BOLD fMRI are still not completely understood and PET imaging requires injection of radioactive tracers. In this study, a pseudo-continuous arterial spin labeling (pCASL) perfusion imaging technique was used to quantify cerebral blood flow (CBF), a well understood physiological index reflective of cerebral metabolism, in N-back working memory tasks. Using pCASL, we systematically investigated brain activation and deactivation induced by the N-back working memory tasks and further studied the load effects on brain activity based on quantitative CBF. Our data show increased CBF in the fronto- parietal cortices, thalamus, caudate, and cerebellar regions, and decreased CBF in the posterior cingulate cortex and medial prefrontal cortex, during the working memory tasks. Most of the activated/deactivated brain regions show an approximately linear relationship between CBF and task loads (0, 1, 2 and 3 back), although several regions show non-linear relationships (quadratic and cubic). The CBF-based spatial patterns of brain activation/deactivation and load effects from this study agree well with those obtained from BOLD fMRI and PET techniques. These results demonstrate the feasibility of ASL techniques to quantify human brain activity during high cognitive tasks, suggesting its potential application to assessing the mechanisms of cognitive deficits in neuropsychiatric and neurological disorders. [Collapse]
• Relationships between Cerebral Blood Flow and IQ in Typically Developing Children and Adolescents
  by Emily Kilroy, Collin Y. Liu, Lirong Yan, Yoon Chun Kim, Mirella Dapretto, Mario F. Mendez, & Danny J. J. Wang
  J. CS. 2011, 12(2), 151-170;
  Abstract The objective of this study was to explore the relationships between IQ and cerebral blood flow (CBF) measured by arterial spin labeling (ASL) in children and adolescents. ASL was used to collect perfusion MRI data on 39 healthy participants aged 7 to 17. The Wechsler Abbreviated Intelligence Scale ... [Read more].
  Abstract The objective of this study was to explore the relationships between IQ and cerebral blood flow (CBF) measured by arterial spin labeling (ASL) in children and adolescents. ASL was used to collect perfusion MRI data on 39 healthy participants aged 7 to 17. The Wechsler Abbreviated Intelligence Scale was administered to determine IQ scores. Multi-variate regression was applied to reveal correlations between CBF and IQ scores, accounting for age, sex and global mean CBF. Voxel Based Morphometry (VBM) analysis, which measures regional cortical volume, was performed as a control. Regression analyses were further performed on CBF data with adjustment of regional gray matter density (GMD). A positive correlation between CBF and IQ scores was primarily seen in the subgenual/anterior cingulate, right orbitofrontal, superior temporal and right inferior parietal regions. An inverse relationship between CBF and IQ was mainly observed in bilateral posterior temporal regions. After adjusting for regional GMD, the correlations between CBF and IQ in the subgenual/anterior cingulate cortex, right orbitofrontal, superior temporal regions and left insula remained significant. These findings support the Parieto-Frontal Integration Theory of intelligence, especially the role of the subgenual/anterior cingulate cortex in the neural networks associated with intelligence. The present study also demonstrates the unique value of CBF in assessing brain-behavior relationships, in addition to structural morphometric measures. [Collapse]
• Effects of Aging on Temporal Lobe Blood Flow with Structural Correction in Healthy Older Adults
  by Siyuan Hu, Hengyi Rao, Lauren Mancuso, Senhua Zhu, John A. Detre, & David A. Wolk
  J. CS. 2011, 12(2), 171-193;
  Abstract Aging has been associated with both cerebral blood flow (CBF) reductions and structural changes, particularly in the medial temporal lobe (MTL) region. However, it remains unclear whether the decline of CBF in the MTL is due entirely or just partially to anatomical changes. In the present study, pse... [Read more].
  Abstract Aging has been associated with both cerebral blood flow (CBF) reductions and structural changes, particularly in the medial temporal lobe (MTL) region. However, it remains unclear whether the decline of CBF in the MTL is due entirely or just partially to anatomical changes. In the present study, pseudocontinuous arterial spin labeling (ASL) was used to measure quantitative CBF in forty-one healthy older adults. High-resolution T1-weighted structure images were also acquired from each subject. Robust age-related CBF decline and anatomical changes were observed in the medial and superior temporal lobe. After controlling for partial volume effect (PVE) and brain atrophy, there were still significant age-related regional CBF decreases in the right parahippocampus and the bilateral insula. However, regional CBF in the left parahippocampal gyrus was not correlated with age after PVE correction. Our results support the importance of structural correction for regional CBF quantification in aging populations and suggest that anatomical changes alone cannot explain the regional CBF decline in older adults. [Collapse]
• Neural Substrates Associated with Weather-Induced Mood Variability: An Exploratory Study Using ASL Perfusion fMRI
  by Seth J. Gillihan, John A. Detre, Martha J. Farah, & Hengyi Rao
  J. CS. 2011, 12(2), 195-210;
  Abstract Daily variations in weather are known to be associated with variations in mood. However, little is known about the specific brain regions that instantiate weather-related mood changes. We used a data-driven approach and ASL perfusion fMRI to assess the neural substrates associated with weather-induc... [Read more].
  Abstract Daily variations in weather are known to be associated with variations in mood. However, little is known about the specific brain regions that instantiate weather-related mood changes. We used a data-driven approach and ASL perfusion fMRI to assess the neural substrates associated with weather-induced mood variability. The data-driven approach was conducted with mood ratings under various weather conditions (N = 464). Forward stepwise regression was conducted to develop a statistical model of mood as a function of weather conditions. The model results were used to calculate the mood-relevant weather index which served as the covariate in the regression analysis of the resting CBF (N = 42) measured by ASL perfusion fMRI under various weather conditions. The resting CBF activities in the left insula-prefrontal cortex and left superior parietal lobe were negatively correlated (corrected p<0.05) with the weather index, indicating that better mood-relevant weather conditions were associated with lower CBF in these regions within the brain’s emotional network. The present study represents a first step toward the investigation of the effect of natural environment on baseline human brain function, and suggests the feasibility of ASL perfusion fMRI for such study. [Collapse]