Despite the prevalence of stress in everyday life and its impact on happiness, health, and cognition, little is known about the neural substrate of the experience of everyday stress in humans. We use a quantitative and noninvasive neuroimaging technique, arterial spin-labeling perfusion MRI, to measure cerebral blood flow (CBF) changes associated with mild to moderate stress induced by a mental arithmetic task with performance monitoring. Elicitation of stress was verified by self-report of stress and emotional state and measures of heart rate and salivary-cortisol level. The change in CBF induced by the stress task was positively correlated with subjective stress rating in the ventral right prefrontal cortex (RPFC) and left insula͞putamen area. The ventral RPFC along with right insula͞putamen and anterior cingulate showed sustained activation after task completion in subjects reporting a high stress level during arithmetic tasks. Additionally, variations of baseline CBF in the ventral RPFC and right orbitofrontal cortex were found to correlate with changes in salivary-cortisol level and heart rate caused by undergoing stress tasks. We further demonstrated that the observed right prefrontal activation could not be attributed to increased cognitive demand accompanying stress tasks and extended beyond neural pathways associated with negative emotions. Our results provide neuroimaging evidence that psychological stress induces negative emotion and vigilance and that the ventral RPFC plays a key role in the central stress response.anterior cingulate cortex ͉ arterial spin labeling ͉ right prefrontal cortex

The purpose of this work was to assess the feasibility and efficacy of using an array coil and parallel imaging in continuous arterial spin labeling (CASL) perfusion MRI. An 8-channel receive-only array head coil was used in conjunction with a surrounding detunable volume transmit coil. The signal to noise ratio (SNR), temporal stability, cerebral blood flow (CBF), and perfusion image coverage were measured from steady state CASL scans using: a standard volume coil, array coil, and array coil with 2-and 3-fold accelerated parallel imaging. Compared to the standard volume coil, the array coil provided 3 times the average SNR increase and higher temporal stability for the perfusion weighted images, even with threefold acceleration. Although perfusion images of the array coil were affected by the inhomogeneous coil sensitivities, this effect was invisible in the quantitative CBF images, which showed highly reproducible perfusion values compared to the standard volume coil. The unfolding distortions of parallel imaging were suppressed in the perfusion images by pairwise subtraction, though they sharply degraded the raw EPI images. Moreover, parallel imaging provided the potential of acquiring more slices due to the short-

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