scholarly journals Quantitative relations between BOLD responses, cortical energetics, and impulse firing

2018 ◽  
Vol 119 (3) ◽  
pp. 979-989 ◽  
Author(s):  
M. R. Bennett ◽  
L. Farnell ◽  
W. G. Gibson
Keyword(s):  
Neural Activity ◽  
Blood Oxygen Level Dependent ◽  
Bold Signal ◽  
Neural Firing ◽  
Functional Magnetic Resonance ◽  
Blood Oxygen Level ◽  
Baseline Activity ◽  
Bold Responses ◽  
Negative Bold ◽  
Quantitative Account

The blood oxygen level-dependent (BOLD) functional magnetic resonance imaging signal arises as a consequence of changes in blood flow and oxygen usage that in turn are modulated by changes in neural activity. Much attention has been given to both theoretical and experimental aspects of the energetics but not to the neural activity. Here we identify the best energetic theory for the steady-state BOLD signal on the basis of correct predictions of experimental observations. This theory is then used, together with the recently determined relationship between energetics and neural activity, to predict how the BOLD signal changes with activity. Unlike existing treatments, this new theory incorporates a nonzero baseline activity in a completely consistent way and is thus able to account for both sustained positive and negative BOLD signals. We also show that the increase in BOLD signal for a given increase in activity is significantly smaller the larger the baseline activity, as is experimentally observed. Furthermore, the decline of the positive BOLD signal arising from deeper cortical laminae in response to an increase in neural firing is shown to arise as a consequence of the larger baseline activity in deeper laminae. Finally, we provide quantitative relations integrating BOLD responses, energetics, and impulse firing, which among other predictions give the same results as existing theories when the baseline activity is zero. NEW & NOTEWORTHY We use a recently established relation between energetics and neural activity to give a quantitative account of BOLD dependence on neural activity. The incorporation of a nonzero baseline neural activity accounts for positive and negative BOLD signals, shows that changes in neural activity give BOLD changes that are smaller the larger the baseline, and provides a basis for the observed inverse relation between BOLD responses and the depth of cortical laminae giving rise to them.

scholarly journals The neural basis of the blood–oxygen–level–dependent functional magnetic resonance imaging signal

2002 ◽  
Vol 357 (1424) ◽  
pp. 1003-1037 ◽  
Author(s):  
Nikos K. Logothetis
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Neural Activity ◽  
Blood Oxygen Level Dependent ◽  
Bold Signal ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Blood Oxygen Level ◽  
Neural Basis ◽  
Neural Signals

Magnetic resonance imaging (MRI) has rapidly become an important tool in clinical medicine and biological research. Its functional variant (functional magnetic resonance imaging; fMRI) is currently the most widely used method for brain mapping and studying the neural basis of human cognition. While the method is widespread, there is insufficient knowledge of the physiological basis of the fMRI signal to interpret the data confidently with respect to neural activity. This paper reviews the basic principles of MRI and fMRI, and subsequently discusses in some detail the relationship between the blood–oxygen–level–dependent (BOLD) fMRI signal and the neural activity elicited during sensory stimulation. To examine this relationship, we conducted the first simultaneous intracortical recordings of neural signals and BOLD responses. Depending on the temporal characteristics of the stimulus, a moderate to strong correlation was found between the neural activity measured with microelectrodes and the BOLD signal averaged over a small area around the microelectrode tips. However, the BOLD signal had significantly higher variability than the neural activity, indicating that human fMRI combined with traditional statistical methods underestimates the reliability of the neuronal activity. To understand the relative contribution of several types of neuronal signals to the haemodynamic response, we compared local field potentials (LFPs), single– and multi–unit activity (MUA) with high spatio–temporal fMRI responses recorded simultaneously in monkey visual cortex. At recording sites characterized by transient responses, only the LFP signal was significantly correlated with the haemodynamic response. Furthermore, the LFPs had the largest magnitude signal and linear systems analysis showed that the LFPs were better than the MUAs at predicting the fMRI responses. These findings, together with an analysis of the neural signals, indicate that the BOLD signal primarily measures the input and processing of neuronal information within a region and not the output signal transmitted to other brain regions.

scholarly journals Distinct neurophysiological correlates of the fMRI BOLD signal in the hippocampus and neocortex

2021 ◽  
Author(s):  
Paul F. Hill ◽  
Sarah E. Seger ◽  
Hye Bin Yoo ◽  
Danielle R. King ◽  
Bradley C. Lega ◽  
...  
Keyword(s):  
Neural Activity ◽  
Blood Oxygen Level Dependent ◽  
Gamma Band ◽  
Bold Signal ◽  
Blood Oxygen Level ◽  
Indirect Measure ◽  
Neural Architecture ◽  
High Gamma ◽  
Gamma Band Activity ◽  
Band Activity

AbstractFunctional magnetic resonance imaging (fMRI) is among the foremost methods for mapping human brain function but provides only an indirect measure of underlying neural activity. Recent findings suggest that the neurophysiological correlates of the fMRI blood-oxygen-level-dependent (BOLD) signal might be regionally specific. We examined the neurophysiological correlates of the fMRI BOLD signal in the hippocampus and neocortex, where differences in neural architecture might result in a different relationship between the respective signals. Fifteen human neurosurgical patients (10 female, 5 male) implanted with depth electrodes performed a verbal free recall task while electrophysiological activity was recorded simultaneously from hippocampal and neocortical sites. The same patients subsequently performed a similar version of the task during a later fMRI session. Subsequent memory effects (SMEs) were computed for both imaging modalities as patterns of encoding-related brain activity predictive of later free recall. Linear mixed-effects modelling revealed that the relationship between BOLD and gamma-band SMEs was moderated by the lobar location of the recording site. BOLD and high gamma (70-150 Hz) SMEs positively covaried across much of the neocortex. This relationship was reversed in the hippocampus, where a negative correlation between BOLD and high gamma SMEs was evident. We also observed a negative relationship between BOLD and low gamma (30-70 Hz) SMEs in the medial temporal lobe more broadly. These results suggest that the neurophysiological correlates of the BOLD signal in the hippocampus differ from those observed in the neocortex.Significance StatementThe blood-oxygen-level-dependent (BOLD) signal forms the basis of fMRI but provides only an indirect measure of neural activity. Task-related modulation of BOLD signals are typically equated with changes in gamma-band activity; however, relevant empirical evidence comes largely from the neocortex. We examined neurophysiological correlates of the BOLD signal in the hippocampus, where the differing neural architecture might result in a different relationship between the respective signals. We identified a positive relationship between encoding-related changes in BOLD and gamma-band activity in frontal, temporal, and parietal cortex. This effect was reversed in the hippocampus, where BOLD and gamma-band effects negatively covaried. These results suggest regional variability in the transfer function between neural activity and the BOLD signal in the hippocampus and neocortex.

Radial Biases in the Processing of Motion and Motion-Defined Contours by Human Visual Cortex

2009 ◽  
Vol 102 (5) ◽  
pp. 2974-2981 ◽  
Author(s):  
Colin W. G. Clifford ◽  
Damien J. Mannion ◽  
J. Scott McDonald
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Human Subjects ◽  
Temporal Integration ◽  
Blood Oxygen Level Dependent ◽  
Orientation Tuning ◽  
Bold Signal ◽  
Functional Magnetic Resonance ◽  
Resonance Imaging ◽  
Blood Oxygen Level

Luminance gratings reportedly produce a stronger functional magnetic resonance imaging (fMRI) blood oxygen level–dependent (BOLD) signal in those parts of the retinotopic cortical maps where they are oriented radially to the point of fixation. We sought to extend this finding by examining anisotropies in the response of cortical areas V1–V3 to motion-defined contour stimuli. fMRI at 3 Tesla was used to measure the BOLD signal in the visual cortex of six human subjects. Stimuli were composed of strips of spatial white noise texture presented in an annular window. The texture in alternate strips moved in opposite directions (left–right or up–down). The strips themselves were static and tilted 45° left or right from vertical. Comparison with maps of the visual field obtained from phase-encoded retinotopic analysis revealed systematic patterns of radial bias. For motion, a stronger response to horizontal was evident within V1 and along the borders between V2 and V3. For orientation, the response to leftward tilted contours was greater in left dorsal and right ventral V1–V3. Radial bias for the orientation of motion-defined contours analogous to that reported previously for luminance gratings could reflect cue-invariant processing or the operation of distinct mechanisms subject to similar anisotropies in orientation tuning. Radial bias for motion might be related to the phenomenon of “motion streaks,” whereby temporal integration by the visual system introduces oriented blur along the axis of motion. We speculate that the observed forms of radial bias reflect a common underlying anisotropy in the representation of spatiotemporal image structure across the visual field.

scholarly journals Neural effects of oxytocin and mimicry in frontotemporal dementia

Neurology ◽  
2020 ◽  
Vol 95 (19) ◽  
pp. e2635-e2647 ◽  
Author(s):  
Lindsay D. Oliver ◽  
Chloe Stewart ◽  
Kristy Coleman ◽  
James H. Kryklywy ◽  
Robert Bartha ◽  
...  
Keyword(s):  
Frontotemporal Dementia ◽  
Facial Expressions ◽  
Neural Activity ◽  
Blood Oxygen Level Dependent ◽  
Brain Regions ◽  
Bold Signal ◽  
Class Iii ◽  
Emotional Facial Expressions ◽  
Blood Oxygen Level

ObjectiveTo determine whether intranasal oxytocin, alone or in combination with instructed mimicry of facial expressions, would augment neural activity in patients with frontotemporal dementia (FTD) in brain regions associated with empathy, emotion processing, and the simulation network, as indexed by blood oxygen–level dependent (BOLD) signal during fMRI.MethodsIn a placebo-controlled, randomized crossover design, 28 patients with FTD received 72 IU intranasal oxytocin or placebo and then completed an fMRI facial expression mimicry task.ResultsOxytocin alone and in combination with instructed mimicry increased activity in regions of the simulation network and in limbic regions associated with emotional expression processing.ConclusionsThe findings demonstrate latent capacity to augment neural activity in affected limbic and other frontal and temporal regions during social cognition in patients with FTD, and support the promise and need for further investigation of these interventions as therapeutics in FTD.ClinicalTrials.gov identifierNCT01937013.Classification of evidenceThis study provides Class III evidence that a single dose of 72 IU intranasal oxytocin augments BOLD signal in patients with FTD during viewing of emotional facial expressions.

Modulation of cortical and subcortical brain areas at low and high exercise intensities

2019 ◽  
Vol 54 (2) ◽  
pp. 110-115 ◽  
Author(s):  
Eduardo Bodnariuc Fontes ◽  
Henrique Bortolotti ◽  
Kell Grandjean da Costa ◽  
Brunno Machado de Campos ◽  
Gabriela K Castanho ◽  
...  
Keyword(s):  
Perceived Exertion ◽  
Insular Cortex ◽  
Blood Oxygen Level Dependent ◽  
Brain Regions ◽  
Bold Signal ◽  
Blood Oxygen Level ◽  
Exercise Protocol ◽  
Brain Areas ◽  
Subcortical Brain ◽  
Negative Bold

IntroductionThe brain plays a key role in the perceptual regulation of exercise, yet neuroimaging techniques have only demonstrated superficial brain areas responses during exercise, and little is known about the modulation of the deeper brain areas at different intensities.Objectives/methodsUsing a specially designed functional MRI (fMRI) cycling ergometer, we have determined the sequence in which the cortical and subcortical brain regions are modulated at low and high ratings perceived exertion (RPE) during an incremental exercise protocol.ResultsAdditional to the activation of the classical motor control regions (motor, somatosensory, premotor and supplementary motor cortices and cerebellum), we found the activation of the regions associated with autonomic regulation (ie, insular cortex) (ie, positive blood-oxygen-level-dependent (BOLD) signal) during exercise. Also, we showed reduced activation (negative BOLD signal) of cognitive-related areas (prefrontal cortex), an effect that increased during exercise at a higher perceived intensity (RPE 13–17 on Borg Scale). The motor cortex remained active throughout the exercise protocol whereas the cerebellum was activated only at low intensity (RPE 6–12), not at high intensity (RPE 13–17).ConclusionsThese findings describe the sequence in which different brain areas become activated or deactivated during exercise of increasing intensity, including subcortical areas measured with fMRI analysis.

scholarly journals Key Aspects of Neurovascular Control Mediated by Specific Populations of Inhibitory Cortical Interneurons

2019 ◽  
Vol 30 (4) ◽  
pp. 2452-2464 ◽  
Author(s):  
L Lee ◽  
L Boorman ◽  
E Glendenning ◽  
C Christmas ◽  
P Sharp ◽  
...  
Keyword(s):  
Blood Volume ◽  
Neural Activity ◽  
Blood Oxygen Level Dependent ◽  
Brain Regions ◽  
Cortical Inhibition ◽  
Blood Oxygen Level ◽  
Hemodynamic Changes ◽  
Cortical Interneurons ◽  
Negative Bold ◽  
Key Aspects

Abstract Inhibitory interneurons can evoke vasodilation and vasoconstriction, making them potential cellular drivers of neurovascular coupling. However, the specific regulatory roles played by particular interneuron subpopulations remain unclear. Our purpose was therefore to adopt a cell-specific optogenetic approach to investigate how somatostatin (SST) and neuronal nitric oxide synthase (nNOS)-expressing interneurons might influence the neurovascular relationship. In mice, specific activation of SST- or nNOS-interneurons was sufficient to evoke hemodynamic changes. In the case of nNOS-interneurons, robust hemodynamic changes occurred with minimal changes in neural activity, suggesting that the ability of blood oxygen level dependent functional magnetic resonance imaging (BOLD fMRI) to reliably reflect changes in neuronal activity may be dependent on type of neuron recruited. Conversely, activation of SST-interneurons produced robust changes in evoked neural activity with shallow cortical excitation and pronounced deep layer cortical inhibition. Prolonged activation of SST-interneurons often resulted in an increase in blood volume in the centrally activated area with an accompanying decrease in blood volume in the surrounding brain regions, analogous to the negative BOLD signal. These results demonstrate the role of specific populations of cortical interneurons in the active control of neurovascular function.

scholarly journals Quantitative relations between transient BOLD responses, cortical energetics, and impulse firing in different cortical regions

2019 ◽  
Vol 122 (3) ◽  
pp. 1226-1237 ◽  
Author(s):  
M. R. Bennett ◽  
L. Farnell ◽  
W. G. Gibson
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Neuronal Activity ◽  
Blood Oxygen Level Dependent ◽  
Blood Oxygen ◽  
Bold Signal ◽  
Oxygen Level ◽  
Blood Oxygen Level ◽  
Baseline Activity ◽  
Input Activity

The blood oxygen level-dependent (BOLD) functional magnetic resonance imaging signal arises as a consequence of changes in blood flow (cerebral blood flow) and oxygen usage (cerebral metabolic rate of oxygen) that in turn are modulated by changes in neuronal activity. Much attention has been given to both theoretical and experimental aspects of the energetics but not to the neuronal activity. Here we use our previous theory relating the steady-state BOLD signal to neuronal activity and amalgamate it with the standard dynamic causal model (DCM, Friston) theory to produce a quantitative model relating the time-dependent BOLD signal to the underlying neuronal activity. Unlike existing treatments, this new theory incorporates a nonzero baseline activity in a completely consistent way and is thus able to account for both positive and negative BOLD signals. It can reproduce a wide variety of experimental BOLD signals reported in the literature solely by adjusting the neuronal input activity. In this way it provides support for the claim that the main features of the signals, including poststimulus undershoot and overshoot, are principally a result of changes in neuronal activity. NEW & NOTEWORTHY A previous model relating the steady-state blood oxygen level-dependent (BOLD) signal to neuronal activity, both above and below baseline, is extended to account for transient BOLD signals. This allows for a detailed investigation of the role neuronal activity can play in such signals and also encompasses poststimulus undershoot and overshoot. A wide variety of experimental BOLD signals are reproduced solely by adjusting the neuronal input activity, including recent results regarding the BOLD signal in patients with schizophrenia.

scholarly journals Task-Evoked BOLD Responses Are Normal in Areas of Diaschisis After Stroke

2008 ◽  
Vol 23 (1) ◽  
pp. 52-57 ◽  
Author(s):  
Damien A. Fair ◽  
Abraham Z. Snyder ◽  
Lisa Tabor Connor ◽  
Binyam Nardos ◽  
Maurizio Corbetta
Keyword(s):  
Blood Flow ◽  
Block Design ◽  
Inferior Frontal Gyrus ◽  
Blood Oxygen Level Dependent ◽  
Bold Signal ◽  
Blood Oxygen Level ◽  
Positron Emission ◽  
Fmri Study ◽  
Bold Responses ◽  
Word Stem Completion

Objective. Cerebral infarction can cause diaschisis, a reduction of blood flow and metabolism in areas of the cortex distant from the site of the lesion. Although the functional magnetic resonance imaging (fMRI) blood oxygen level dependent (BOLD) signal is increasingly used to examine the neural correlates of recovery in stroke, its reliability in areas of diaschisis is uncertain. Design. The effect of chronic diaschisis as measured by resting positron emission tomography on task-evoked BOLD responses during word-stem completion in a block design fMRI study was examined in 3 patients, 6 months after a single left hemisphere stroke involving the inferior frontal gyrus and operculum. Results. The BOLD responses were minimally affected in areas of chronic diaschisis. Conclusions. Within the confines of this study, the mechanism underlying the BOLD signal, which includes a mismatch between neuronally driven increases in blood flow and a corresponding increase in oxygen use, appears to be intact in areas of chronic diaschisis.

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