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Cortical Layer-Dependent Hemodynamic Regulation Investigated by Functional Magnetic Resonance Imaging

Yen, Cecil Chern-Chyi (2011) Cortical Layer-Dependent Hemodynamic Regulation Investigated by Functional Magnetic Resonance Imaging. Doctoral Dissertation, University of Pittsburgh.

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    Abstract

    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.


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    Item Type: University of Pittsburgh ETD
    ETD Committee:
    ETD Committee TypeCommittee MemberEmailORCID
    Committee ChairKim, Seong-Gikimsg@pitt.edu
    Committee MemberStetten, George D.stetten@andrew.cmu.edu
    Committee MemberAizenstein, Howard J.aizen@pitt.edu
    Committee MemberCrowley, Justin C.jcrowley@andrew.cmu.edu
    Title: Cortical Layer-Dependent Hemodynamic Regulation Investigated by Functional Magnetic Resonance Imaging
    Status: Unpublished
    Abstract: 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.
    Date: 19 September 2011
    Date Type: Completion
    Defense Date: 13 April 2011
    Approval Date: 19 September 2011
    Submission Date: 23 March 2011
    Access Restriction: No restriction; The work is available for access worldwide immediately.
    Patent pending: No
    Institution: University of Pittsburgh
    Thesis Type: Doctoral Dissertation
    Refereed: Yes
    Degree: PhD - Doctor of Philosophy
    URN: etd-03232011-173811
    Uncontrolled Keywords: CBV; Layer; fMRI; Hemodynamic; MRI; BOLD
    Schools and Programs: Swanson School of Engineering > Bioengineering
    Date Deposited: 10 Nov 2011 14:32
    Last Modified: 14 Feb 2012 16:28
    Other ID: http://etd.library.pitt.edu/ETD/available/etd-03232011-173811/, etd-03232011-173811

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