Visual stimulation frequency dependent changes in bold transients
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1
Bogazici University, Türkiye
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2
Istanbul University, Türkiye
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3
Uskudar University, Türkiye
Blood oxygenation level dependent (BOLD) signal change is used to map neuronal activity in the brain. In most fMRI experiments, time course of each image voxel is correlated with the stimulus pattern convolved with hypothetical waveform; hemodynamic response function (HRF) which plays an important role in active voxel detection. We investigated experimentally the frequency response characteristics of two BOLD transients, the initial overshoot and the positive BOLD (pBOLD), with flickering light at varying frequencies to test whether a single hemodynamic response function may hold for visual input at different frequencies. The blood oxygenation level-dependent (BOLD) responses to 6, 8, 10, 12, 14, 18, 22, 26, 30, 34, 38, 42 and 46 Hz flicker visual stimulations in the primary visual cortex were investigated in 22 healthy volunteers. Software tools within FSL were used in fMRI data processing. Single subject, single session analysis results were thresholded at a significance level of p < .05 (corrected) and masked with MNI (Montreal Neurological Institute) occipital lobe mask. The percent change of the BOLD response of most significantly active 150 voxels was averaged. Initial overshoot (6-18 s after stimulus onset) and positive BOLD (18-45 s after stimulus onset) were quantified as the average value of the BOLD response in the corresponding intervals. With increasing visual input frequency the pBOLD response declined much stronger compared with the initial overshoot leading to a significant difference between both transients for the frequencies higher than 14 Hz (p < .05). This result suggests that both parts of the BOLD signal correspond to different neuronal activities and that they should be modeled separately for a better description of the process. Funding: This study is supported by TUBITAK project #108S101.
Keywords:
BOLD signal,
Brain Signals
Conference:
XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011.
Presentation Type:
Poster Presentation
Topic:
Poster Sessions: Modeling and Analysis of Brain Signals
Citation:
Bayram
A,
Ademoğlu
A,
Karahan
E,
Bilgiç
B,
Duru
A,
Tarhan
N and
Demiralp
T
(2011). Visual stimulation frequency dependent changes in bold transients.
Conference Abstract:
XI International Conference on Cognitive Neuroscience (ICON XI).
doi: 10.3389/conf.fnhum.2011.207.00081
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Received:
16 Nov 2011;
Published Online:
25 Nov 2011.
*
Correspondence:
Dr. Ali Bayram, Bogazici University, Istanbul, Türkiye, benalibayram@gmail.com