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61
Modeling the hemodynamic response to brain activation
- Neuroimage
, 2004
"... Neural activity in the brain is accompanied by changes in cerebral blood flow (CBF) and blood oxygenation that are detectable with functional magnetic resonance imaging (fMRI) techniques. In this paper, recent mathematical models of this hemodynamic response are reviewed and integrated. Models are d ..."
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Cited by 84 (4 self)
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Neural activity in the brain is accompanied by changes in cerebral blood flow (CBF) and blood oxygenation that are detectable with functional magnetic resonance imaging (fMRI) techniques. In this paper, recent mathematical models of this hemodynamic response are reviewed and integrated. Models are described for: (1) the blood oxygenation level dependent (BOLD) signal as a function of changes in cerebral oxygen extraction fraction (E) and cerebral blood volume (CBV); (2) the balloon model, proposed to describe the transient dynamics of CBV and deoxyhemoglobin (Hb) and how they affect the BOLD signal; (3) neurovascular coupling, relating the responses in CBF and cerebral metabolic rate of oxygen (CMRO2) to the neural activity response; and (4) a simple model for the temporal nonlinearity of the neural response itself. These models are integrated into a mathematical framework describing the steps linking a stimulus to the measured BOLD and CBF responses. Experimental results examining transient features of the BOLD response (post-stimulus undershoot and initial dip), nonlinearities of the hemodynamic response, and the role of the physiologic baseline state in altering the BOLD signal are discussed in the context of the proposed models. Quantitative modeling of the hemodynamic response, when combined with experimental data measuring both the BOLD and CBF responses, makes possible a more specific and quantitative assessment of brain physiology than is possible with standard BOLD imaging alone. This approach has the potential to enhance numerous studies of brain function in development, health, and disease.
The intraparietal sulcus and perceptual organization
- Journal of Cognitive Neuroscience
, 2005
"... & The structuring of the sensory scene (perceptual organi-zation) profoundly affects what we perceive, and is of increas-ing clinical interest. In both vision and audition, many cues have been identified that influence perceptual organization, but only a little is known about its neural basis. P ..."
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Cited by 43 (6 self)
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& The structuring of the sensory scene (perceptual organi-zation) profoundly affects what we perceive, and is of increas-ing clinical interest. In both vision and audition, many cues have been identified that influence perceptual organization, but only a little is known about its neural basis. Previous studies have suggested that auditory cortex may play a role in auditory perceptual organization (also called auditory stream segrega-tion). However, these studies were limited in that they just examined auditory cortex and that the stimuli they used to generate different organizations had different physical charac-teristics, which per se may have led to the differences in neural response. In the current study, functional magnetic resonance imaging was used to test for an effect of perceptual organiza-tion across the whole brain. To avoid confounding physical changes to the stimuli with differences in perceptual organiza-tion, we exploited an ambiguous auditory figure that is some-times perceived as a single auditory stream and sometimes as two streams. We found that regions in the intraparietal sulcus (IPS) showed greater activity when 2 streams were perceived rather than 1. The specific involvement of this region in per-ceptual organization is exciting, as there is a growing literature that suggests a role for the IPS in binding in vision, touch, and cross-modally. This evidence is discussed, and a general role proposed for regions of the IPS in structuring sensory input. &
Neural bases of cognitive ERPs: More than phase reset. J Cogn Neurosci 16:1595–1604
, 2004
"... & Up to now, two conflicting theories have tried to explain the genesis of averaged event-related potentials (ERPs): Whereas one hypothesis claims that ERPs originate from an event-related activation of neural assemblies distinct from back-ground dynamics, the other hypothesis states that ERPs a ..."
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Cited by 27 (5 self)
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& Up to now, two conflicting theories have tried to explain the genesis of averaged event-related potentials (ERPs): Whereas one hypothesis claims that ERPs originate from an event-related activation of neural assemblies distinct from back-ground dynamics, the other hypothesis states that ERPs are produced by phase resetting of ongoing oscillatory activity. So far, this question has only been addressed for early ERP components. Late ERP components, however, are generally thought to represent superimposed activities of several ana-tomically distinct brain areas. Thus, the question of which mechanism underlies the genesis of late ERP components cannot be easily answered based on scalp recordings. In con-trast, two well-investigated late ERP components recorded in-vasively from within the human medial temporal lobe (MTL) in epilepsy patients, the so-called MTL-P300 and the ante-rior MTL-N400 (AMTL-N400), are based on single source activ-ity. Hence, we investigated whether the MTL-P300 and the AMTL-N400 are based on an event-related activity increase, a phase reset of ongoing oscillatory activity or both. ERPs were recorded from the hippocampus and rhinal cortex in subjects performing a visual oddball paradigm and a visual word rec-ognition paradigm. With wavelet techniques, stimulus-related phase-locking and power changes were analyzed in a fre-quency range covering 2 to 48 Hz. We found that the MTL-P300 is accompanied by both phase reset and power increase and that both effects overlap partly in time. In contrast, the AMTL-N400 is initially associated with phase locking with-out power increase and only later during the course of the AMTL-N400 we observed an additional power increase. In con-clusion, both aspects, event-related activation of neural as-semblies and phase resetting of ongoing activity seem to be involved in the generation of late ERP components as re-corded in cognitive tasks. Therefore, separate analysis of event-related power and phase-locking changes might reveal specific insights into the mechanisms underlying different cognitive functions. &
Interpretable classifiers for FMRI improve prediction of purchases
- IEEE Trans. Neural Systems and Rehabilitation Engineering
"... Abstract—Despite growing interest in applying machine learning to neuroimaging analyses, few studies have gone beyond classifying sensory input to directly predicting behavioral output. With spatial resolution on the order of millimeters and temporal resolution on the order of seconds, functional ma ..."
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Cited by 23 (3 self)
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Abstract—Despite growing interest in applying machine learning to neuroimaging analyses, few studies have gone beyond classifying sensory input to directly predicting behavioral output. With spatial resolution on the order of millimeters and temporal resolution on the order of seconds, functional magnetic resonance imaging (fMRI) is a promising technology for such applications. However, fMRI data’s low signal-to-noise ratio, high dimensionality, and extensive spatiotemporal correlations present formidable analytic challenges. Here, we apply different machine-learning algorithms to previously acquired data to examine the ability of fMRI activation in three regions—the nucleus accumbens (NAcc), medial prefrontal cortex (MPFC), and insula—to predict purchasing. Our goal was to improve spatiotemporal interpretability as well as classification accuracy. To this end, sparse penalized discriminant analysis (SPDA) enabled automatic selection of correlated variables, yielding interpretable models that generalized well to new data. Relative to logistic regression, linear discriminant analysis, and linear support vector machines, SPDA not only increased interpretability but also improved classification accuracy. SPDA promises to allow more precise inferences about when specific brain regions contribute to purchasing decisions. More broadly, this approach provides a general framework for using neuroimaging data to build interpretable models, including those that predict choice. Index Terms—Accumbens, classification, discriminant, elastic net, frontal, functional magnetic resonance imaging (fMRI),
Imagery or meaning? Evidence for a semantic origin of category-specific brain activity in metabolic imaging
, 2008
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Good Vibrations: Cross-frequency Coupling in the Human Nucleus Accumbens during Reward Processing
"... & The nucleus accumbens is critical for reward-guided learning and decision-making. It is thought to ‘‘gate’ ’ the flow of a diverse range of information (e.g., rewarding, aversive, and novel events) from limbic afferents to basal ganglia outputs. Gating and information encoding may be achieved ..."
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Cited by 20 (3 self)
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& The nucleus accumbens is critical for reward-guided learning and decision-making. It is thought to ‘‘gate’ ’ the flow of a diverse range of information (e.g., rewarding, aversive, and novel events) from limbic afferents to basal ganglia outputs. Gating and information encoding may be achieved via crossfrequency coupling, in which bursts of high-frequency activity occur preferentially during specific phases of slower oscillations. We examined whether the human nucleus accumbens engages such a mechanism by recording electrophysiological activity directly from the accumbens of human patients undergoing deep brain stimulation surgery. Oscillatory activity in the gamma (40–80 Hz) frequency range was synchronized with the phase of simultaneous alpha (8–12 Hz) waves. Further, losing and winning small amounts of money elicited relatively increased gamma oscillation power prior to and following alpha troughs, respectively. Gamma–alpha synchronization may reflect an electrophysiological gating mechanism in the human nucleus accumbens, and the phase differences in gamma–alpha coupling may reflect a reward information coding scheme similar to phase coding. &
Nonlinear coupling of neural activity and CBF in rodent barrel cortex. Neuroimage 22
, 2004
"... The relationship between neural activity and accompanying changes in cerebral blood flow (CBF) and oxygenation must be fully understood before data from brain imaging techniques can be correctly interpreted. Whether signals in fMRI reflect the neural input or output of an activated region is still u ..."
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Cited by 15 (6 self)
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The relationship between neural activity and accompanying changes in cerebral blood flow (CBF) and oxygenation must be fully understood before data from brain imaging techniques can be correctly interpreted. Whether signals in fMRI reflect the neural input or output of an activated region is still unclear. Similarly, quantitative relationships between neural activity and changes in CBF are not well understood. The present study addresses these issues by using simultaneous laser Doppler flowmetry (LDF) to measure CBF and multichannel electrophysiology to record neural activity in the form of field potentials and multiunit spiking. We demonstrate that CBF-activation coupling is a nonlinear inverse sigmoid function. Comparing the data with previous work suggests that within a cortical model, CBF shows greatest spatial correlation with a current sink 500 Am below the surface corresponding to sensory input. These results show that care must be exercised when interpreting imaging data elicited by particularly strong or weak stimuli and that hemodynamic changes may better reflect the input to a region rather than its spiking output.
Effector-independent voluntary timing: Behavioural and neuroimaging evidence
- European Journal of Neuroscience
, 2005
"... We investigated effector-independent aspects of voluntary motor timing, using behavioural measurements and functional magnetic resonance imaging. Two types of temporal pattern were investigated; one isochronous, the other a metric, rhythmic sequence of six temporal intervals. Each pattern was perfor ..."
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Cited by 12 (1 self)
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We investigated effector-independent aspects of voluntary motor timing, using behavioural measurements and functional magnetic resonance imaging. Two types of temporal pattern were investigated; one isochronous, the other a metric, rhythmic sequence of six temporal intervals. Each pattern was performed using tapping movements with the left or right index fingers, or rhythmic speech on one syllable. Deviations from the ideal temporal pattern in the rhythmic sequence tasks were consistent between the three different effectors, within subjects. This suggests that the same representation of the rhythm was used to time the movements with all effectors. To reveal brain regions involved in such effector-independent timing, we localized the overlap in brain activity when the rhythmic sequence was performed with the different effectors. Activity was found in the mesial and lateral premotor cortices, posterior and anterior regions of the superior temporal gyrus and the inferior frontal cortex. Subcortical activations were in the left globus pallidus, the vermis and bilaterally in the cerebellar hemispheres (lobule VI) and the thalamus. The overlap in activity between the isochronous tasks included the same set of brain regions, except for the basal ganglia and the thalamus. Rhythmic sequences had significantly higher activity in mesial premotor cortex, the left superior temporal gyrus and the cerebellum, than had isochronous movements. These findings reveal a set of brain regions likely to be involved in effector-independent representations of temporal patterns in voluntary motor timing. A subset of these regions plays important roles for the organization of rhythmic sequences of several intervals.
Differential activation of frontoparietal attention networks by social and symbolic spatial cues. Social Cognitive and Affective Neuroscience 5
, 2010
"... Perception of both gaze-direction and symbolic directional cues (e.g. arrows) orient an observer’s attention toward the indicated location. It is unclear, however, whether these similar behavioral effects are examples of the same attentional phenomenon and, therefore, subserved by the same neural su ..."
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Cited by 8 (0 self)
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Perception of both gaze-direction and symbolic directional cues (e.g. arrows) orient an observer’s attention toward the indicated location. It is unclear, however, whether these similar behavioral effects are examples of the same attentional phenomenon and, therefore, subserved by the same neural substrate. It has been proposed that gaze, given its evolutionary significance, constitutes a ’special ’ category of spatial cue. As such, it is predicted that the neural systems supporting spatial reorienting will be different for gaze than for non-biological symbols. We tested this prediction using functional magnetic resonance imaging to measure the brain’s response during target localization in which laterally presented targets were preceded by uninformative gaze or arrow cues. Reaction times were faster during valid than invalid trials for both arrow and gaze cues. However, differential patterns of activity were evoked in the brain. Trials including invalid rather than valid arrow cues resulted in a stronger hemodynamic response in the ventral attention network. No such difference was seen during trials including valid and invalid gaze cues. This differential engagement of the ventral reorienting network is consistent with the notion that the facilitation of target detection by gaze cues and arrow cues is subserved by different neural substrates.
