scholarly journals Eccentricity Mapping of the Human Visual Cortex to Evaluate Temporal Dynamics of Functional T1ρ Mapping

2015 ◽  
Vol 35 (7) ◽  
pp. 1213-1219 ◽  
Author(s):  
Hye-Young Heo ◽  
John A Wemmie ◽  
Casey P Johnson ◽  
Daniel R Thedens ◽  
Vincent A Magnotta
Keyword(s):  
Blood Flow ◽  
Visual Cortex ◽  
Temporal Dynamics ◽  
Occipital Cortex ◽  
Hemodynamic Response ◽  
Proton Exchange ◽  
Blood Oxygenation ◽  
Human Visual Cortex ◽  
Tissue Metabolism ◽  
Oxygenation Level

Recent experiments suggest that T1 relaxation in the rotating frame ( T1ρ) is sensitive to metabolism and can detect localized activity-dependent changes in the human visual cortex. Current functional magnetic resonance imaging (fMRI) methods have poor temporal resolution due to delays in the hemodynamic response resulting from neurovascular coupling. Because T1ρ is sensitive to factors that can be derived from tissue metabolism, such as pH and glucose concentration via proton exchange, we hypothesized that activity-evoked T1ρ changes in visual cortex may occur before the hemodynamic response measured by blood oxygenation level-dependent (BOLD) and arterial spin labeling (ASL) contrast. To test this hypothesis, functional imaging was performed using BOLD, and ASL in human participants viewing an expanding ring stimulus. We calculated eccentricity phase maps across the occipital cortex for each functional signal and compared the temporal dynamics of T1ρ versus BOLD and ASL. The results suggest that T1ρ changes precede changes in the two blood flow-dependent measures. These observations indicate that T1ρ detects a signal distinct from traditional fMRI contrast methods. In addition, these findings support previous evidence that T1ρ is sensitive to factors other than blood flow, volume, or oxygenation. Furthermore, they suggest that tissue metabolism may be driving activity-evoked T1ρ changes.

scholarly journals Dynamics of the cerebral blood flow response to brief neural activity in human visual cortex

2019 ◽  
Vol 40 (9) ◽  
pp. 1823-1837 ◽  
Author(s):  
Jung Hwan Kim ◽  
Amanda J Taylor ◽  
Danny JJ Wang ◽  
Xiaowei Zou ◽  
David Ress
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Visual Cortex ◽  
Temporal Dynamics ◽  
Oxygen Metabolism ◽  
Late Time ◽  
Neural Activation ◽  
Hemodynamic Response Function ◽  
Time Dynamics ◽  
Human Visual Cortex

The blood oxygen-level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal depends on an interplay of cerebral blood flow (CBF), oxygen metabolism, and cerebral blood volume. Despite wide usage of BOLD fMRI, it is not clear how these physiological components create the BOLD signal. Here, baseline CBF and its dynamics evoked by a brief stimulus (2 s) in human visual cortex were measured at 3T. We found a stereotypical CBF response: immediate increase, rising to a peak a few second after the stimulus, followed by a significant undershoot. The BOLD hemodynamic response function (HRF) was also measured in the same session. Strong correlations between HRF and CBF peak responses indicate that the flow responses evoked by neural activation in nearby gray matter drive the early HRF. Remarkably, peak CBF and HRF were also strongly modulated by baseline perfusion. The CBF undershoot was reliable and significantly correlated with the HRF undershoot. However, late-time dynamics of the HRF and CBF suggest that oxygen metabolism can also contribute to the HRF undershoot. Combined measurement of the CBF and HRF for brief neural activation is a useful tool to understand the temporal dynamics of neurovascular and neurometabolic coupling.

Blood oxygenation level-dependent (BOLD) total and extravascular signal changes and ΔR 2 * in human visual cortex at 1.5, 3.0 and 7.0 T

2010 ◽  
Vol 24 (1) ◽  
pp. 25-34 ◽  
Author(s):  
Manus J. Donahue ◽  
Hans Hoogduin ◽  
Peter C. M. van Zijl ◽  
Peter Jezzard ◽  
Peter R. Luijten ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Blood Oxygenation Level Dependent ◽  
Blood Oxygenation ◽  
Human Visual Cortex ◽  
Blood Oxygenation Level ◽  
Oxygenation Level ◽  
Signal Changes

Gain control in the response of human visual cortex to plaids

2012 ◽  
Vol 107 (9) ◽  
pp. 2570-2580 ◽  
Author(s):  
J. Scott McDonald ◽  
Damien J. Mannion ◽  
Colin W. G. Clifford
Keyword(s):  
Visual Cortex ◽  
Tree Shrew ◽  
Gain Control ◽  
Imaging Study ◽  
Blood Oxygenation ◽  
Human Visual Cortex ◽  
Intrinsic Signal ◽  
Orientation Response ◽  
Oxygenation Level ◽  
The Individual

A recent intrinsic signal optical imaging study in tree shrew showed, surprisingly, that the population response of V1 to plaid patterns comprising grating components of equal contrast is predicted by the average of the responses to the individual components (MacEvoy SP, Tucker TR, Fitzpatrick D. Nat Neurosci 12: 637–645, 2009). This prompted us to compare responses to plaids and gratings in human visual cortex as a function of contrast and orientation. We found that the functional MRI (fMRI) blood oxygenation level-dependent (BOLD) responses of areas V1–V3 to a plaid comprising superposed grating components of equal contrast are significantly higher than the responses to a single component. Furthermore, the orientation response profile of a plaid is poorly predicted from a linear combination of the responses to its components. Together, these results indicate that the model of MacEvoy et al. (2009) cannot, without modification, account for the fMRI BOLD response to plaids in human visual cortex.

scholarly journals Altered neurochemical coupling in the occipital cortex in migraine with visual aura

Cephalalgia ◽  
2015 ◽  
Vol 35 (11) ◽  
pp. 1025-1030 ◽  
Author(s):  
Holly Bridge ◽  
Charlotte J Stagg ◽  
Jamie Near ◽  
Chi-ieong Lau ◽  
Aimee Zisner ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Visual Stimulation ◽  
Occipital Cortex ◽  
Blood Oxygenation Level Dependent ◽  
Blood Oxygenation ◽  
Resonance Spectroscopy ◽  
Bold Signal ◽  
Visual Aura ◽  
Oxygenation Level ◽  
Neurochemical Profile

Background Visual aura is present in about one-third of migraine patients and triggering by bright or flickering lights is frequently reported. Method Using migraine with visual aura patients, we investigated the neurochemical profile of the visual cortex using magnetic resonance spectroscopy. Specifically, glutamate/creatine and GABA/creatine ratios were quantified in the occipital cortex of female migraine patients. Results GABA levels in the occipital cortex of migraine patients were lower than that of controls. Glutamate levels in migraine patients, but not controls, correlated with the blood-oxygenation-level-dependent (BOLD) signal in the primary visual cortex during visual stimulation. Conclusion Migraine with visual aura appears to disrupt the excitation-inhibition coupling in the occipital cortex.

Attenuated Brain Response to Auditory Word Stimulation with Sevoflurane

2005 ◽  
Vol 103 (1) ◽  
pp. 11-19 ◽  
Author(s):  
Chantal Kerssens ◽  
Stephan Hamann ◽  
Scott Peltier ◽  
Xiaoping P. Hu ◽  
Michael G. Byas-Smith ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Occipital Cortex ◽  
Blood Oxygenation Level Dependent ◽  
Blood Oxygenation ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Brain Response ◽  
Auditory Word ◽  
Blood Oxygenation Level ◽  
Oxygenation Level

Background Functional magnetic resonance imaging offers a compelling, new perspective on altered brain function but is sparsely used in studies of anesthetic effect. To examine effects on verbal memory encoding, the authors imaged human brain response to auditory word stimulation using functional magnetic resonance imaging at different concentrations of an agent not previously studied, and tested memory after recovery. Methods Six male volunteers were studied breathing 0.0, 2.0, and 1.0% end-tidal sevoflurane (awake, deep, and light states, respectively) via laryngeal mask. In each condition, they heard 15 two-syllable English nouns via closed headphones. Each word was repeated 15 times (1/s), followed by 15 s of rest. Blood oxygenation level-dependent brain activations during blocks of stimulation versus rest were assessed with a 3-T Siemens Trio scanner and a 20-voxel spatial extent threshold. Memory was tested approximately 1.5 h after recovery with an auditory recognition task (chance performance = 33% correct). Results Scans showed widespread activations (P < 0.005, uncorrected) in the awake state, including bilateral superior temporal, frontal, and parietal cortex, right occipital cortex, bilateral thalamus, striatum, hippocampus, and cerebellum; more limited activations in the light state (bilateral superior temporal gyrus, right thalamus, bilateral parietal cortex, left frontal cortex, and right occipital cortex); and no significant auditory-related activation in the deep state. During recognition testing, subjects correctly selected 77 +/- 12% of words presented while they were awake as "old," versus 32 +/- 15 and 42 +/- 8% (P < 0.01) correct for the light and deep stages, respectively. Conclusions Sevoflurane induces dose-dependent suppression of auditory blood oxygenation level-dependent signals, which likely limits the ability of words to be processed during anesthesia and compromises memory.

scholarly journals Temporal Dynamics of Corticocortical Inhibition in Human Visual Cortex: A TMS Study

Neuroscience ◽  
2019 ◽  
Vol 421 ◽  
pp. 31-38
Author(s):  
Dalia Khammash ◽  
Molly Simmonite ◽  
Thad A. Polk ◽  
Stephan F. Taylor ◽  
Sean K. Meehan
Keyword(s):  
Visual Cortex ◽  
Temporal Dynamics ◽  
Human Visual Cortex
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