Dependency of BOLD transients on the frequency of flickering visual stimuli
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1
Bogazici University, Türkiye
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2
Istanbul University, Türkiye
BOLD-based fMRI has been shown to reflect combined effects of several physiological parameters like cerebral blood flow (CBF), cerebral blood volume (CBV) and cerebral metabolic rate of oxygen (CMRO2) during the neuronal activity. Combined effects of these parameters could be observed as three transients in BOLD response as the initial dip, the positive BOLD (PBOLD) and the post-stimulus undershoot (PSU). Differences in the amplitude of these transients could reflect differences in the neurovascular coupling and/or differences in neuronal activity. The dependency of PBOLD-based fMRI on the temporal frequency of the stimulation has been studied before and an increase in PBOLD has been reported up to 8 Hz, which was followed by either a decrease or a plateau for higher stimulation frequencies. In this study, we focused on both PBOLD and PSU responses to the stimulation frequencies beyond 8 Hz and explored additional local peaks emerging from a stimulation scheme with a finer frequency resolution. Additionally, we analyzed the correlation between the PBOLD and PSU across different stimulation frequencies to investigate the underlying physiological mechanisms. The dependency of PBOLD and PSU on the temporal frequency of visual stimulation was investigated using stimulation frequencies between 1 and 44 Hz at 24 different stimulation rates. Nine healthy subjects (mean age 28±5) were recruited for this study. Photic stimulation was applied by using white light-emitting diodes coupled to a fiber bundle. To keep the energy of the visual stimuli constant across frequencies, the duty cycle was 50%. For each stimulation frequency of each subject, average BOLD signal time course was computed from the activated voxels within primary visual cortex. The PBOLD peak at 8 Hz in primary visual cortex was in line with previous neuroimaging studies. In addition to the 8 Hz peak, secondary peaks were observed for stimulation frequencies at 16 and 24 Hz. These additional local peaks were contrary to earlier fMRI studies which reported either a decrease or a plateau for frequencies above 8 Hz but in line with electrophysiological results obtained in animal local field potential measurements and human steady-state visual evoked potential (SSVEP) recordings. Our results also indicate that the dependency of PSU amplitude on stimulus frequency deviates from that of PBOLD. Although their amplitudes were correlated within the 1–13 Hz range, they changed independently at stimulation frequencies between 13 and 44 Hz. The different dependency profiles of PBOLD and PSU to stimulation frequency points to different underlying neurovascular mechanisms responsible for the generation of these BOLD transients, which could be regard to their relation to inhibitory and excitatory neuronal activity.
Conference:
10th International Conference on Cognitive Neuroscience, Bodrum, Türkiye, 1 Sep - 5 Sep, 2008.
Presentation Type:
Poster Presentation
Topic:
Neuroinformatics of Cognition
Citation:
Emir
U,
Bayraktaroglu
Z,
Öztürk
C,
Ademoglu
A and
Demiralp
T
(2008). Dependency of BOLD transients on the frequency of flickering visual stimuli.
Conference Abstract:
10th International Conference on Cognitive Neuroscience.
doi: 10.3389/conf.neuro.09.2009.01.346
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Received:
15 Dec 2008;
Published Online:
15 Dec 2008.
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Correspondence:
Zübeyir Bayraktaroglu, Istanbul University, Istanbul, Türkiye, zbay@istanbul.edu.tr