Functional magnetic resonance imaging (fMRI) is currently one of the most widely used non-invasive neuroimaging modalities for mapping brain activation. Techniques such as blood oxygenation level dependent (BOLD) fMRI or cerebral blood volume (CBV)-weighted fMRI are based on the assumption that hemodynamic responses are tightly regulated by neural activity. However, the relationship between fMRI responses and neural activity is still unclear. To investigate this relationship, the unique properties of temporal frequency tuning of primary visual cortex neurons was used as a model since it can be used to separate the neural input and output activities of this area. During moving grating stimuli of 1, 2, 10 and 20 Hz temporal frequencies, two fMRI studies, areal and laminar studies, were conducted with different spatial resolution in a 9.4-T Varian spectrometer. In areal studies, BOLD fMRI was able to detect the difference in tuning properties between area 17 (A17), area 18 (A18) and lateral geniculate nucleus. In A17, the BOLD tuning curve seemed to reflect the local field potential (LFP) low frequency band (<12 Hz) rather than spiking activity and LFP gamma band (25-90 Hz). In laminar studies, a high spatial resolution protocol was adopted to resolve the different cortical layers in A17. In addition to BOLD fMRI, CBV-weighted fMRI was performed to eliminate the contamination from the superficial draining veins. These results showed that BOLD and CBV tuning curves do not reflect the underlying spiking activity or the LFP activity at infragranular layers (the bottom layer of three cortical layers). This implies that the hemodynamic response may not be regulated on a laminar level. Therefore, caution should be taken when interpreting BOLD responses as the sole indicator of different aspects of neural activity in areal and laminar scales.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-03232011-173811 |
| Date | 19 September 2011 |
| Creators | Yen, Cecil Chern-Chyi |
| Contributors | Justin C. Crowley, George D. Stetten, Howard J. Aizenstein, Mitsuhiro Fukuda, Seong-Gi Kim |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-03232011-173811/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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