Continuous ASL perfusion fMRI investigation of higher cognition: Quantification of tonic CBF changes during sustained attention and working memory tasks

Abstract

Arterial spin labeling (ASL) perfusion fMRI is an emerging method in clinical neuroimaging. Its non-invasiveness, absence of low frequency noise, and ability to quantify the absolute level of cerebral blood flow (CBF) make the method ideal for longitudinal designs or low frequency paradigms. Despite the usefulness in the study of cognitive dysfunctions in clinical populations, perfusion activation studies to date have been conducted for simple sensorimotor paradigms or with single-slice acquisition, mainly due to technical challenges. Using our recently developed amplitudemodulated continuous ASL (CASL) perfusion fMRI protocol, we assessed the feasibility of a higher level cognitive activation study in twelve healthy subjects. Taking advantage of the ASL noise properties, we were able to study tonic CBF changes during uninterrupted 6-min continuous performance of working memory and sustained attention tasks. For the visual sustained attention task, regional CBF increases (6-12 ml/100 g/min) were detected in the right middle frontal gyrus, the bilateral occipital gyri, and the anterior cingulate/medial frontal gyri. During the 2-back working memory task, significantly increased activations (7-11 ml/100 g/min) were found in the left inferior frontal/precentral gyri, the left inferior parietal lobule, the anterior cingulate/medial frontal gyri, and the left occipital gyrus. Locations of activated and deactivated areas largely concur with previous PET and BOLD fMRI studies utilizing similar paradigms. These results demonstrate that CASL perfusion fMRI can be successfully utilized for the investigation of the tonic CBF changes associated with high level cognitive operations. Increased applications of the method to the investigation of cognitively impaired populations are expected to follow.

Coupling of functional connectivity and regional cerebral blood flow reveals a physiological basis for network hubs of the human brain

“…Previous studies have demonstrated that both FCS (7,18,33) and rCBF (19,20) undergo modulations in response to cognitive, effort-demanding tasks. However, whether this relationship between FCS and rCBF would still be present during task performance was hitherto unknown.…”

“…Therefore, the first goal of this study is to investigate whether intrinsic functional network connectivity is closely related to rCBF in resting human brains. If so, given that both functional network connectivity (7, 18) and rCBF (19,20) undergo changes in response to varying cognitive tasks, the second goal is to examine whether this connectivity-rCBF relationship is preserved during a working-memory task and modulated by changes in cognitive task load.To address these issues, we collected functional MRI (fMRI) data of blood-oxygenation-level-dependent (BOLD) and arterialspin-labeling (ASL) perfusion contrasts in 48 healthy adults during rest, and, in a subset of 39 subjects during an N-back workingmemory task. BOLD data were used to identify hubs of functional networks, and ASL perfusion data were exploited to measure rCBF of the brain.…”

“…Therefore, the first goal of this study is to investigate whether intrinsic functional network connectivity is closely related to rCBF in resting human brains. If so, given that both functional network connectivity (7, 18) and rCBF (19,20) undergo changes in response to varying cognitive tasks, the second goal is to examine whether this connectivity-rCBF relationship is preserved during a working-memory task and modulated by changes in cognitive task load.…”

Attention-Deficit/Hyperactivity Disorder and Attention Networks

“…Work in this vein has been based on hypothesized interruption of attention network activity by altered default network activity (Weissman et al, 2006), which in ADHD has been thought to lead to greater variability in ADHD performance (Sonuga-Barke and Castellanos, 2007). ASL techniques, which can provide absolute measures of rCBF during rest (Aguirre et al, 2005;Detre and Wang, 2002;Kim et al, 2006;Wang et al, 2005) should help better define the pathophysiology of ADHD and other psychiatric disorders (Broyd et al, 2009). Dopaminergic studies.…”

Narrative speech production: An fMRI study using continuous arterial spin labeling

“…We circumvented potential problems associated with fMRI data collection during speech by using sparse data sampling, taking advantage of the delay in the hemodynamic response to collect cortical activation data following the cessation of speech (Belin et al, 1998;Hall et al, 1999). We also elected to use perfusion fMRI based on an arterial spin labeling (ASL) perfusion technique rather than Blood Oxygen-Level Dependent (BOLD) fMRI because ASL contrast does not depend on susceptibility effects, and ASL perfusion fMRI can be obtained using imaging sequences that minimize artifacts from static susceptibility gradients (FernandezSeara et al, 2005;Kemeny, Ye, Birn, & Braun, 2005;Kim et al, 2006). Further, because labeled and control images are interleaved during ASL scanning, ASL perfusion fMRI data do not suffer from the low frequency noise that is typically present in BOLD data, and sustained task conditions can be studied without any penalty (Wang et al, 2003).…”