M Corbetta

Publications of M Corbetta

• The role of nonlinearity in computing graph-theoretical properties of resting-state functional magnetic resonance imaging brain networks.

  Authors: D Hartman, J Hlinka, M Palus, D Mantini, M Corbetta

  Chaos (Woodbury, N.Y.). 03/2011; 21(1):013119.

  In recent years, there has been an increasing interest in the study of large-scale brain activity interaction structure from the perspective of complex networks, based on functional magneticIn recent years, there has been an increasing interest in the study of large-scale brain activity interaction structure from the perspective of complex networks, based on functional magnetic resonance imaging (fMRI) measurements. To assess the strength of interaction (functional connectivity, FC) between two brain regions, the linear (Pearson) correlation coefficient of the respective time series is most commonly used. Since a potential use of nonlinear FC measures has recently been discussed in this and other fields, the question arises whether particular nonlinear FC measures would be more informative for the graph analysis than linear ones. We present a comparison of network analysis results obtained from the brain connectivity graphs capturing either full (both linear and nonlinear) or only linear connectivity using 24 sessions of human resting-state fMRI. For each session, a matrix of full connectivity between 90 anatomical parcel time series is computed using mutual information. For comparison, connectivity matrices obtained for multivariate linear Gaussian surrogate data that preserve the correlations, but remove any nonlinearity are generated. Binarizing these matrices using multiple thresholds, we generate graphs corresponding to linear and full nonlinear interaction structures. The effect of neglecting nonlinearity is then assessed by comparing the values of a range of graph-theoretical measures evaluated for both types of graphs. Statistical comparisons suggest a potential effect of nonlinearity on the local measures-clustering coefficient and betweenness centrality. Nevertheless, subsequent quantitative comparison shows that the nonlinearity effect is practically negligible when compared to the intersubject variability of the graph measures. Further, on the group-average graph level, the nonlinearity effect is unnoticeable.

• Multimodal integration of fMRI and EEG data for high spatial and temporal resolution analysis of brain networks.

  Authors: D Mantini, L Marzetti, M Corbetta, G L Romani, C Del Gratta

  Brain topography. 06/2010; 23(2):150-8.

  Two major non-invasive brain mapping techniques, electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), have complementary advantages with regard to their spatial and temporalTwo major non-invasive brain mapping techniques, electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), have complementary advantages with regard to their spatial and temporal resolution. We propose an approach based on the integration of EEG and fMRI, enabling the EEG temporal dynamics of information processing to be characterized within spatially well-defined fMRI large-scale networks. First, the fMRI data are decomposed into networks by means of spatial independent component analysis (sICA), and those associated with intrinsic activity and/or responding to task performance are selected using information from the related time-courses. Next, the EEG data over all sensors are averaged with respect to event timing, thus calculating event-related potentials (ERPs). The ERPs are subjected to temporal ICA (tICA), and the resulting components are localized with the weighted minimum norm (WMNLS) algorithm using the task-related fMRI networks as priors. Finally, the temporal contribution of each ERP component in the areas belonging to the fMRI large-scale networks is estimated. The proposed approach has been evaluated on visual target detection data. Our results confirm that two different components, commonly observed in EEG when presenting novel and salient stimuli, respectively, are related to the neuronal activation in large-scale networks, operating at different latencies and associated with different functional processes.

• Electrophysiological signatures of resting state networks in the human brain.

  Authors: D Mantini, M G Perrucci, C Del Gratta, G L Romani, M Corbetta

  Proceedings of the National Academy of Sciences of the United States of America. 08/2007; 104(32):13170-5.

  Functional neuroimaging and electrophysiological studies have documented a dynamic baseline of intrinsic (not stimulus- or task-evoked) brain activity during resting wakefulness. This baseline isFunctional neuroimaging and electrophysiological studies have documented a dynamic baseline of intrinsic (not stimulus- or task-evoked) brain activity during resting wakefulness. This baseline is characterized by slow (<0.1 Hz) fluctuations of functional imaging signals that are topographically organized in discrete brain networks, and by much faster (1-80 Hz) electrical oscillations. To investigate the relationship between hemodynamic and electrical oscillations, we have adopted a completely data-driven approach that combines information from simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). Using independent component analysis on the fMRI data, we identified six widely distributed resting state networks. The blood oxygenation level-dependent signal fluctuations associated with each network were correlated with the EEG power variations of delta, theta, alpha, beta, and gamma rhythms. Each functional network was characterized by a specific electrophysiological signature that involved the combination of different brain rhythms. Moreover, the joint EEG/fMRI analysis afforded a finer physiological fractionation of brain networks in the resting human brain. This result supports for the first time in humans the coalescence of several brain rhythms within large-scale brain networks as suggested by biophysical studies.

• Intrinsic functional architecture in the anaesthetized monkey brain.

  Authors: J L Vincent, G H Patel, M D Fox, A Z Snyder, J T Baker, D C Van Essen, J M Zempel, L H Snyder, M Corbetta, M E Raichle

  Nature. 06/2007; 447(7140):83-6.

  The traditional approach to studying brain function is to measure physiological responses to controlled sensory, motor and cognitive paradigms. However, most of the brain's energy consumption isThe traditional approach to studying brain function is to measure physiological responses to controlled sensory, motor and cognitive paradigms. However, most of the brain's energy consumption is devoted to ongoing metabolic activity not clearly associated with any particular stimulus or behaviour. Functional magnetic resonance imaging studies in humans aimed at understanding this ongoing activity have shown that spontaneous fluctuations of the blood-oxygen-level-dependent signal occur continuously in the resting state. In humans, these fluctuations are temporally coherent within widely distributed cortical systems that recapitulate the functional architecture of responses evoked by experimentally administered tasks. Here, we show that the same phenomenon is present in anaesthetized monkeys even at anaesthetic levels known to induce profound loss of consciousness. We specifically demonstrate coherent spontaneous fluctuations within three well known systems (oculomotor, somatomotor and visual) and the 'default' system, a set of brain regions thought by some to support uniquely human capabilities. Our results indicate that coherent system fluctuations probably reflect an evolutionarily conserved aspect of brain functional organization that transcends levels of consciousness.

• Neural basis and recovery of spatial attention deficits in spatial neglect

  Authors: M. Corbetta, M. J. Kincade, C. Lewis, A. Z. Snyder, A. Sapir

  Nature Neuroscience. 01/2005; 8(11):1603-10.

  The syndrome of spatial neglect is typically associated with focal injury to the temporoparietal or ventral frontal cortex. This syndrome shows spontaneous partial recovery, but the neural basis ofThe syndrome of spatial neglect is typically associated with focal injury to the temporoparietal or ventral frontal cortex. This syndrome shows spontaneous partial recovery, but the neural basis of both spatial neglect and its recovery is largely unknown. We show that spatial attention deficits in neglect (rightward bias and reorienting) after right frontal damage correlate with abnormal activation of structurally intact dorsal and ventral parietal regions that mediate related attentional operations in the normal brain. Furthermore, recovery of these attention deficits correlates with the restoration and rebalancing of activity within these regions. These results support a model of recovery based on the re-weighting of activity within a distributed neuronal architecture, and they show that behavioral deficits depend not only on structural changes at the locus of injury, but also on physiological changes in distant but functionally related brain areas.

• Multiple neural correlates of detection in the human brain.

  Authors: G L Shulman, J M Ollinger, M Linenweber, S E Petersen, M Corbetta

  Proceedings of the National Academy of Sciences of the United States of America. 02/2001; 98(1):313-8.

  We used event-related functional MRI to examine the neural consequences of detecting the presence or absence of a stimulus. Subjects detected a brief interval of coherent motion embedded in dynamicWe used event-related functional MRI to examine the neural consequences of detecting the presence or absence of a stimulus. Subjects detected a brief interval of coherent motion embedded in dynamic noise that was presented throughout a test period. Several brain regions, including V1/V2, middle temporal complex (MT+), left intraparietal cortex, and the frontal eye field, were activated at the onset of the dynamic noise, irrespective of whether a coherent motion target was presented early or late in the test period, or not at all. These regions, many of which were motion sensitive, were likely involved in searching for and detecting the target. The blood oxygenation level-dependent signal in these regions was higher in trials in which a target was detected than in trials in which it was missed or not presented, indicating that these regions were modulated by detection. Moreover, the blood oxygenation leveldependent signal in these regions decayed quickly once a target was detected, even though the dynamic noise continued to be displayed, indicating that they were shut down after detection. Therefore, detection-related modulations occurred in the same regions that accumulate target information over time, in agreement with current psychological and neural models of detection. Many other regions, however, including areas in prefrontal cortex and anterior cingulate, were not involved in searching for a target. In these regions, activation began early in the test period when an early target was detected but began late in the test period when a late target was detected or when a response was correctly withheld in the absence of a motion target. The signal in these regions was therefore triggered by a discrete event during the test interval that was related to presence-absence detection.

• Separating processes within a trial in event-related functional MRI.

  Authors: J M Ollinger, G L Shulman, M Corbetta

  NeuroImage. 02/2001; 13(1):210-7.

  Many behavioral paradigms involve temporally overlapping sensory, cognitive, and motor components within a single trial. The complex interplay among these factors makes it desirable to separate theMany behavioral paradigms involve temporally overlapping sensory, cognitive, and motor components within a single trial. The complex interplay among these factors makes it desirable to separate the components of the total response without assumptions about shape of the underlying hemodynamic response. We present a method that does this. Four conditions were studied in four subjects to validate the method. Two conditions involved rapid event-related studies, one with a low-contrast (5%) flickering checkerboard and another with a high-contrast (95%) checkerboard. In the third condition, the same high-contrast checkerboard was presented with widely spaced trials. Finally, multicomponent trials were formed from temporally adjacent low-contrast and high-contrast stimuli. These trials were presented as a rapid event-related study. Low-contrast stimuli presented in isolation (partial trials) made it possible to uniquely estimate both the low-contrast and high-contrast responses. These estimated responses matched those measured in the first three conditions, thereby validating the method. Nonlinear interactions between adjacent low-contrast and high-contrast responses were shown to be significant but weak in two of the four subjects.

• Separating processes within a trial in event-related functional MRI.

  Authors: J M Ollinger, M Corbetta, G L Shulman

  NeuroImage. 02/2001; 13(1):218-29.

  Many cognitive processes occur on time scales that can significantly affect the shape of the blood oxygenation level-dependent (BOLD) response in event-related functional MRI. This shape can beMany cognitive processes occur on time scales that can significantly affect the shape of the blood oxygenation level-dependent (BOLD) response in event-related functional MRI. This shape can be estimated from event related designs, even if these processes occur in a fixed temporal sequence (J. M. Ollinger, G. L. Shulman, and M. Corbetta. 2001. NeuroImage 13: 210-217). Several important considerations come into play when interpreting these time courses. First, in single subjects, correlations among neighboring time points give the noise a smooth appearance that can be confused with changes in the BOLD response. Second, the variance and degree of correlation among estimated time courses are strongly influenced by the timing of the experimental design. Simulations show that optimal results are obtained if the intertrial intervals are as short as possible, if they follow an exponential distribution with at least three distinct values, and if 40% of the trials are partial trials. These results are not particularly sensitive to the fraction of partial trials, so accurate estimation of time courses can be obtained with lower percentages of partial trials (20-25%). Third, statistical maps can be formed from F statistics computed with the extra sum of square principle or by t statistics computed from the cross-correlation of the time courses with a model for the hemodynamic response. The latter method relies on an accurate model for the hemodynamic response. The most robust model among those tested was a single gamma function. Finally, the power spectrum of the measured BOLD signal in rapid event-related paradigms is similar to that of the noise. Nevertheless, high-pass filtering is desirable if the appropriate model for the hemodynamic response is used.

• Voluntary orienting is dissociated from target detection in human posterior parietal cortex.

  Authors: M Corbetta, J M Kincade, J M Ollinger, M P McAvoy, G L Shulman

  Nature neuroscience. 04/2000; 3(3):292-7.

  Human ability to attend to visual stimuli based on their spatial locations requires the parietal cortex. One hypothesis maintains that parietal cortex controls the voluntary orienting of attentionHuman ability to attend to visual stimuli based on their spatial locations requires the parietal cortex. One hypothesis maintains that parietal cortex controls the voluntary orienting of attention toward a location of interest. Another hypothesis emphasizes its role in reorienting attention toward visual targets appearing at unattended locations. Here, using event-related functional magnetic resonance (ER-fMRI), we show that distinct parietal regions mediated these different attentional processes. Cortical activation occurred primarily in the intraparietal sulcus when a location was attended before visual-target presentation, but in the right temporoparietal junction when the target was detected, particularly at an unattended location.

• Areas involved in encoding and applying directional expectations to moving objects.

  Authors: G L Shulman, J M Ollinger, E Akbudak, T E Conturo, A Z Snyder, S E Petersen, M Corbetta

  The Journal of neuroscience : the official journal of the Society for Neuroscience. 12/1999; 19(21):9480-96.

  Two experiments used functional magnetic resonance imaging (fMRI) to examine the cortical areas involved in establishing an expectation about the direction of motion of an upcoming object andTwo experiments used functional magnetic resonance imaging (fMRI) to examine the cortical areas involved in establishing an expectation about the direction of motion of an upcoming object and applying that expectation to the analysis of the object. In Experiment 1, subjects saw a stationary cue that either indicated the direction of motion of a subsequent test stimulus (directional cue) or provided no directional information (neutral cue). Their task was to detect the presence of coherent motion in the test stimulus. The stationary directional cue produced larger modulations than the neutral cue, with respect to a passive viewing baseline, both in motion-sensitive areas such as left MT+ and the anterior intraparietal sulcus, as well as motion-insensitive areas such as the posterior intraparietal sulcus and the junction of the left medial precentral sulcus and superior frontal sulcus. Experiment 2 used an event-related fMRI technique to separate signals during the cue period, in which the expectation was encoded and maintained, from signals during the subsequent test period, in which the expectation was applied to the test object. Cue period activations from a stationary, directional cue included many of the same motion-sensitive and -insensitive areas from Experiment 1 that produced directionally specific modulations. Prefrontal activations were not observed during the cue period, even though the stationary cue information had to be translated into a format appropriate for influencing motion detection, and this format was maintained for the duration of the cue period (approximately 5 sec).

• A common network of functional areas for attention and eye movements.

  Authors: M Corbetta, E Akbudak, T E Conturo, A Z Snyder, J M Ollinger, H A Drury, M R Linenweber, S E Petersen, M E Raichle, D C Van Essen, G L Shulman

  Neuron. 11/1998; 21(4):761-73.

  Functional magnetic resonance imaging (fMRI) and surface-based representations of brain activity were used to compare the functional anatomy of two tasks, one involving covert shifts of attention toFunctional magnetic resonance imaging (fMRI) and surface-based representations of brain activity were used to compare the functional anatomy of two tasks, one involving covert shifts of attention to peripheral visual stimuli, the other involving both attentional and saccadic shifts to the same stimuli. Overlapping regional networks in parietal, frontal, and temporal lobes were active in both tasks. This anatomical overlap is consistent with the hypothesis that attentional and oculomotor processes are tightly integrated at the neural level.

• Human cortical mechanisms of visual attention during orienting and search.

  Authors: M Corbetta, G L Shulman

  Philosophical transactions of the Royal Society of London. Series B, Biological sciences. 09/1998; 353(1373):1353-62.

  Functional anatomical studies indicate that a set of neural signals in parietal and frontal cortex mediates the covert allocation of attention to visual locations across a wide variety of visualFunctional anatomical studies indicate that a set of neural signals in parietal and frontal cortex mediates the covert allocation of attention to visual locations across a wide variety of visual tasks. This frontoparietal network includes areas, such as the frontal eye field and supplementary eye field. This anatomical overlap suggests that shifts of attention to visual locations of objects recruit areas involved in oculomotor programming and execution. Finally, the fronto-parietal network may be the source of spatial attentional modulations in the ventral visual system during object recognition or discrimination.

• Frontoparietal cortical networks for directing attention and the eye to visual locations: identical, independent, or overlapping neural systems?

  Authors: M Corbetta

  Proceedings of the National Academy of Sciences of the United States of America. 03/1998; 95(3):831-8.

  Functional anatomical and single-unit recording studies indicate that a set of neural signals in parietal and frontal cortex mediates the covert allocation of attention to visual locations, asFunctional anatomical and single-unit recording studies indicate that a set of neural signals in parietal and frontal cortex mediates the covert allocation of attention to visual locations, as originally proposed by psychological studies. This frontoparietal network is the source of a location bias that interacts with extrastriate regions of the ventral visual system during object analysis to enhance visual processing. The frontoparietal network is not exclusively related to visual attention, but may coincide or overlap with regions involved in oculomotor processing. The relationship between attention and eye movement processes is discussed at the psychological, functional anatomical, and cellular level of analysis.

• Imaging studies of memory and attention.

  Authors: J G Ojemann, R L Buckner, M Corbetta, M E Raichle

  Neurosurgery clinics of North America. 08/1997; 8(3):307-19.

  Functional brain imaging studies of memory and attention with positron emission tomography and functional magnetic resonance imaging demonstrate involvement of specific regions of the normal humanFunctional brain imaging studies of memory and attention with positron emission tomography and functional magnetic resonance imaging demonstrate involvement of specific regions of the normal human brain. Possible anatomical substrates for different types of memory have been identified. Different aspects of attention mechanisms, such as modulation of early visual areas, shifts of attention, and selection of response, also appear to involve specific anatomic regions revealed by imaging. Many of these studies show activation in regions clinically considered to be "silent" regions.

• Searching for activations that generalize over tasks.

  Authors: G L Shulman, M Corbetta, J A Fiez, R L Buckner, F M Miezin, M E Raichle, S E Petersen

  Human brain mapping. 01/1997; 5(4):317-22.

  Nine previous positron emission tomography (PET) studies of human visual information processing were reanalyzed to determine the consistency of blood flow changes during a wide variety of activeNine previous positron emission tomography (PET) studies of human visual information processing were reanalyzed to determine the consistency of blood flow changes during a wide variety of active tasks relative to passive viewing of the same stimulus array. Consistent modulations were found in the early visual cortex, probably including area 17, and these modulations could reflect selective mechanisms. Blood flow decreases were found in some auditory and somatosensory areas, but did not appear to reflect a broad suppression of subcortical input. Outside the sensory cortex, consistent increases across experiments were found in the thalamus and cerebellum, but not in the cerebral cortex. Many cortical areas, however, did show consistent decreases.

• Preserved speech abilities and compensation following prefrontal damage.

  Authors: R L Buckner, M Corbetta, J Schatz, M E Raichle, S E Petersen

  Proceedings of the National Academy of Sciences of the United States of America. 03/1996; 93(3):1249-53.

  Lesions to left frontal cortex in humans produce speech production impairments (nonfluent aphasia). These impairments vary from subject to subject and performance on certain speech production tasksLesions to left frontal cortex in humans produce speech production impairments (nonfluent aphasia). These impairments vary from subject to subject and performance on certain speech production tasks can be relatively preserved in some patients. A possible explanation for preservation of function under these circumstances is that areas outside left prefrontal cortex are used to compensate for the injured brain area. We report here a direct demonstration of preserved language function in a stroke patient (LF1) apparently due to the activation of a compensatory brain pathway. We used functional brain imaging with positron emission tomography (PET) as a basis for this study.

• Superior parietal cortex activation during spatial attention shifts and visual feature conjunction.

  Authors: M Corbetta, G L Shulman, F M Miezin, S E Petersen

  Science (New York, N.Y.). 12/1995; 270(5237):802-5.

  Positron emission tomography was used to measure changes in the regional cerebral blood flow of normal people while they searched visual displays for targets defined by color, by motion, or by aPositron emission tomography was used to measure changes in the regional cerebral blood flow of normal people while they searched visual displays for targets defined by color, by motion, or by a conjunction of color and motion. A region in the superior parietal cortex was activated only during the conjunction task, at a location that had previously been shown to be engaged by successive shifts of spatial attention. Correspondingly, the time needed to detect a conjunction target increased with the number of items in the display, which is consistent with the use of a mechanism that successively analyzes each item in the visual field.

• PET studies of parietal involvement in spatial attention: comparison of different task types.

  Authors: S E Petersen, M Corbetta, F M Miezin, G L Shulman

  Canadian journal of experimental psychology = Revue canadienne de psychologie expérimentale. 07/1994; 48(2):319-38.

  Five experiments are described that concern the mechanisms that direct attention to spatial and non-spatial features of a stimulus and the effects that attention has on the visual system's analysisFive experiments are described that concern the mechanisms that direct attention to spatial and non-spatial features of a stimulus and the effects that attention has on the visual system's analysis of that stimulus. Shifts of attention from one spatial location to another activated the superior parietal lobe and this activation was fairly independent of the task performed on the attended object, the response made to the attended object, and whether the shift of attention was controlled endogenously or exogenously. Maintaining attention tonically on a location or a particular visual feature such as shape, colour or motion did not produce a superior parietal response. Tonic attention to a feature (colour, shape, motion) or location, however, did produce enhancements in the response of various regions that are probably specialized for processing the attended visual feature. The activation of superior parietal cortex during shifts of spatial attention as well as the activation of parietal-occipital cortex when attention is tonically maintained on a location suggest that the parietal cortex plays an important role in spatial computations.

• Positron emission tomography as a tool to study human vision and attention.

  Authors: M Corbetta

  Proceedings of the National Academy of Sciences of the United States of America. 01/1994; 90(23):10901-3.

• A PET study of visuospatial attention.

  Authors: M Corbetta, F M Miezin, G L Shulman, S E Petersen

  The Journal of neuroscience : the official journal of the Society for Neuroscience. 04/1993; 13(3):1202-26.

  Positron emission tomography (PET) was used to identify the neural systems involved in shifting spatial attention to visual stimuli in the left or right visual field along foveofugal or foveocentricPositron emission tomography (PET) was used to identify the neural systems involved in shifting spatial attention to visual stimuli in the left or right visual field along foveofugal or foveocentric directions. Psychophysical evidence indicated that stimuli at validly cued locations were responded to faster than stimuli at invalidly cued locations. Reaction times to invalid probes were faster when they were presented in the same than in the opposite direction of an ongoing attention movement. PET evidence indicated that superior parietal and superior frontal cortex were more active when attention was shifted to peripheral locations than when maintained at the center of gaze. Both regions encoded the visual field and not the direction of an attention shift. In the right superior parietal lobe, two distinct responses were localized for attention to left and right visual field. Finally, the superior parietal region was active when peripheral locations were selected on the basis of cognitive or sensory cues independent of the execution of an overt response. The frontal region was active only when responses were made to stimuli at selected peripheral locations. These findings indicate that parietal and frontal regions control different aspects of spatial selection. The functional asymmetry in superior parietal cortex may be relevant for the pathophysiology of unilateral neglect.