Retinotopic variations of the negative blood-oxygen-level dependent hemodynamic response function in human primary visual cortex

2021 ◽  
Vol 125 (4) ◽  
pp. 1045-1057 ◽  
Author(s):  
Natasha de la Rosa ◽  
David Ress ◽  
Amanda J. Taylor ◽  
Jung Hwan Kim
Keyword(s):  
Visual Cortex ◽  
Response Function ◽  
Complex Dynamics ◽  
Hemodynamic Response ◽  
Blood Oxygen Level Dependent ◽  
Blood Oxygen ◽  
Oxygen Level ◽  
Hemodynamic Response Function ◽  
Blood Oxygen Level ◽  
Early Visual Cortex

We investigate dynamics of the negative hemodynamic response function (nHRF), the negative blood-oxygen-level-dependent (BOLD) response (NBR) evoked by a brief stimulus, in human early visual cortex. Here, we show that the nHRFs are not inverted versions of the corresponding pHRFs. The nHRF has complex dynamics that varied significantly with eccentricity. The results also show shift-invariant temporal linearity does not hold for the NBR.

scholarly journals Hemodynamic response function in resting brain: disambiguating neural events and autonomic effects

2015 ◽  
Author(s):  
Guorong Wu ◽  
Daniele Marinazzo
Keyword(s):  
Point Process ◽  
Resting State ◽  
Process Analysis ◽  
Cardiac Activity ◽  
Hemodynamic Response ◽  
Blood Oxygen Level Dependent ◽  
Blood Oxygen ◽  
Bold Signal ◽  
Hemodynamic Response Function ◽  
Blood Oxygen Level

It has been shown that resting state brain dynamics can be characterized by looking at sparse blood-oxygen-level dependent (BOLD) events, which can be retrieved by point process analysis. Cardiac activity can also induce changes in the BOLD signal, thus affect both the number of these events and the mapping between neural events and BOLD signal, namely the hemodynamic response. To isolate neural activity and autonomic effects, we compare the resting state hemodynamic response retrieved by means of a point process analysis with and without deconvolving the cardiac fluctuations. Brainstem and the surrounding cortical area (such as precuneus, insula etc.) are found to be significantly affected by cardiac pulses. Methodological and physiological implications are then discussed.

scholarly journals Improved Activation and Hemodynamic Response Function of Olfactory fMRI Using Simultaneous Multislice with Reduced TR Acquisition

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Hong Chen ◽  
Jianzhong Yin ◽  
Che He ◽  
Yalin Wu ◽  
Miaomiao Long ◽  
...  
Keyword(s):  
Response Function ◽  
Time Synchronization ◽  
Statistical Significance ◽  
Hemodynamic Response ◽  
Blood Oxygen Level Dependent ◽  
Hemodynamic Response Function ◽  
Blood Oxygen Level ◽  
Time To Peak ◽  
Significant Difference ◽  
Simultaneous Multislice

Objectives. The respiration could decrease the time synchronization between odor stimulation and data acquisition, consequently deteriorating the functional activation and hemodynamic response function (HRF) in olfactory functional magnetic resonance imaging (fMRI) with a conventional repetition time (TR). In this study, we aimed to investigate whether simultaneous multislice (SMS) technology with reduced TR could improve the blood oxygen level-dependent (BOLD) activation and optimize HRF modeling in olfactory fMRI. Methods. Sixteen young healthy subjects with normal olfaction underwent olfactory fMRI on a 3T MRI scanner using a 64 channel head coil. FMRI data were acquired using SMS acceleration at three different TRs: 3000 ms, 1000 ms, and 500 ms. Both metrics of BOLD activation (activated voxels, mean, and maximum t -scores) and the HRF modeling (response height and time to peak) were calculated in the bilateral amygdalae, hippocampi, and insulae. Results. The 500 ms and 1000 ms TRs both significantly improved the number of activated voxels, mean, and maximum t -score in the amygdalae and insulae, compared with a 3000 ms TR (all P < 0.05 ). But the increase of these metrics in the hippocampi did not reach a statistical significance (all P > 0.05 ). No significant difference in any BOLD activation metrics between TR 500 ms and 1000 ms was observed in all regions of interest (ROIs) (all P > 0.05 ). The HRF curves showed that higher response height and shorter time to peak in all ROIs were obtained at 500 ms and 1000 ms TRs compared to 3000 ms TR. TR 500 ms had a more significant effect on response height than TR 1000 ms in the amygdalae ( P = 0.017 ), and there was no significant difference in time to peak between TR 500 ms and 1000 ms in all ROIs (all P > 0.05 ). Conclusions. The fast image acquisition technique of SMS with reduced TR could significantly improve the functional activation and HRF curve in olfactory fMRI.

scholarly journals Covert neurofeedback without awareness shapes cortical network spontaneous connectivity

2016 ◽  
Vol 113 (17) ◽  
pp. E2413-E2420 ◽  
Author(s):  
Michal Ramot ◽  
Shany Grossman ◽  
Doron Friedman ◽  
Rafael Malach
Keyword(s):  
Visual Cortex ◽  
Functional Connectivity ◽  
Functional Mri ◽  
Blood Oxygen Level Dependent ◽  
Blood Oxygen ◽  
Oxygen Level ◽  
Neurofeedback Training ◽  
Learning Situation ◽  
Blood Oxygen Level ◽  
Training Effects

Recent advances in blood oxygen level-dependent–functional MRI (BOLD-fMRI)-based neurofeedback reveal that participants can modulate neuronal properties. However, it is unknown whether such training effects can be introduced in the absence of participants' awareness that they are being trained. Here, we show unconscious neurofeedback training, which consequently produced changes in functional connectivity, introduced in participants who received positive and negative rewards that were covertly coupled to activity in two category-selective visual cortex regions. The results indicate that brain networks can be modified even in the complete absence of intention and awareness of the learning situation, raising intriguing possibilities for clinical interventions.

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