Showing papers by "Jin Hyung Lee published in 2010"

Global and local fMRI signals driven by neurons defined optogenetically by type and wiring

Abstract: Despite a rapidly-growing scientific and clinical brain imaging literature based on functional magnetic resonance imaging (fMRI) using blood oxygenation level-dependent (BOLD) signals, it remains controversial whether BOLD signals in a particular region can be caused by activation of local excitatory neurons. This difficult question is central to the interpretation and utility of BOLD, with major significance for fMRI studies in basic research and clinical applications. Using a novel integrated technology unifying optogenetic control of inputs with high-field fMRI signal readouts, we show here that specific stimulation of local CaMKIIalpha-expressing excitatory neurons, either in the neocortex or thalamus, elicits positive BOLD signals at the stimulus location with classical kinetics. We also show that optogenetic fMRI (of MRI) allows visualization of the causal effects of specific cell types defined not only by genetic identity and cell body location, but also by axonal projection target. Finally, we show that of MRI within the living and intact mammalian brain reveals BOLD signals in downstream targets distant from the stimulus, indicating that this approach can be used to map the global effects of controlling a local cell population. In this respect, unlike both conventional fMRI studies based on correlations and fMRI with electrical stimulation that will also directly drive afferent and nearby axons, this of MRI approach provides causal information about the global circuits recruited by defined local neuronal activity patterns. Together these findings provide an empirical foundation for the widely-used fMRI BOLD signal, and the features of of MRI define a potent tool that may be suitable for functional circuit analysis as well as global phenotyping of dysfunctional circuitry.

Balanced steady state free precession fMRI

Abstract: Balanced-steady-state free precession (b-SSFP) functional magnetic resonance imaging (fMRI) encompasses several recently developed methods that utilize b-SSFP acquisition for fMRI. Short repetition time (TR) and readout durations of b-SSFP allow distortion-free acquisition, 3D imaging, and high-resolution isotropic voxel acquisition. b-SSFP fMRI can be categorized into two different classes depending on which contrast mechanism it exploits. Transition-band b-SSFP fMRI is a technique that utilizes the sharp transition of the b-SSFP profile relying on the fact that oxygenated and deoxegenated hemoglobin has different resonance frequencies. On the other hand, passband b-SSFP fMRI utilizes b-SSFP in the relatively large flat portion of the b-SSFP off-resonance spectrum where oxygenation contrast is expected to be generated from the rapid refocusing in the presence of off-resonance due to oxy- and deoxy-hemoglobin. While both methods share the advantage of b-SSFP acquisition such as distortion-free, 3D high-resolution functional imaging, the main distinction of the two methods come from the contrast mechanism and spatial coverage. In this article, the two classes of b-SSFP-based functional brain imaging methods' characteristics will be compared and discussed. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 23–30, 2010

Lee et al. reply

Abstract: Replying to N. K. Logothetis , 10.1038/nature09532 (2010) This is a welcome opportunity to discuss ofMRI, a technology for testing the causal and global impact of defined cell populations in vivo1. The accompanying Comment2 reviews well-known neuroanatomy, but does seem, in its entirety, to be founded on a suggestion that, after experiments were conducted to drive a defined circuit element and measure resulting BOLD signals1, we concluded that no other contributory circuit element was recruited by the driven population. This was not the case, however, as correctly understood by others in the fMRI community3,4,5 and as explained in the paper (for example, “contributions from additional cells and processes downstream of the defined optically triggered population are expected and indeed represent an important aspect of this approach”1). Moreover, the complexity of the brain dictates that such possible contributory mechanisms are more numerous than listed in the Comment2, including many other circuit and feedback mechanisms and classes of cells within neural circuitry6,7,8,9,10. As was discussed1, this is one of the most important and useful aspects of the ofMRI approach. https://www.nature.com/articles/nature09532