N Logothetis

..Here I give an overview of the current state of fMRI, and draw on neuroimaging and physiological data to present the current understanding of the haemodynamic signals and the constraints they impose on neuroimaging data interpretation...

..Here, we provide a detailed description of the interference compensation system that can be used to record field and action potentials intracortically within a high-field scanner...

..Such a mechanism would cause minimal interference, enabling consolidation of hippocampus-dependent memory...

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..On Ca2+ binding, the water exchange is slightly accelerated, which is likely related to the increased steric demand of the central part leading to a destabilization of the Ln-water binding interaction...

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..Their experiments therefore do not pin down the identity of the specific neuronal signals that give rise to the BOLD signal...

..Moreover, the use of MRI-visible tracers and of electrical microstimulation applied during imaging proves to be ideal for the study of connectivity in the living animal...

..Taken together, our findings suggest that electrical stimulation disrupts cortico-cortical signal propagation by silencing the output of any neocortical area whose afferents are electrically stimulated...

..We propose that the spatial summation of LFP and MUA is determined by the size of these signals' generators and the nature of neural events underlying them, rather than by biophysical properties of gray matter...

..The implications of this technique for combined fMRI/electrophysiology experiments and its limitations in terms of spatial coverage are discussed...

..The mechanisms of rivalry are probably the same as, or very similar to, those underlying multistable perception in general, and further physiological studies might reveal much about the neural mechanisms of our perceptual organization...

..Similar responses were obtained in alert, behaving monkeys performing a discrimination task...

..Our findings suggests that regarding their neural encoding faces are unlikely to be 'special', but they rather are the default 'special class' of the primate visual system...

..We conclude by considering applications of invasive MRI, including injections of paramagnetic tracers for the study of connectivity in the living animal and simultaneous imaging and electrical microstimulation...

..These findings suggest that the BOLD contrast mechanism reflects the input and intracortical processing of a given area rather than its spiking output...

..The chronic recording techniques and methods of analyses we report can be used to characterize the changes in brain circuits due to learning...

..While these results confirm the notion of the claustrum as a multisensory structure per se, they argue against the hypothesis of the claustrum serving as an integrator of sensory information...

..These multisensory processes in the auditory cortex likely occur via reciprocal interactions with the superior temporal sulcus...

..Importantly, our results provide a neural counterpart for the human imaging and lesion findings and uncover a basis for a supposed role of the insula in processing vocal communication sounds such as speech...

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..Our findings suggest a refinement of current models of cortical microcircuit architecture and function: Either adjacent neurons share only a few percent of their inputs or, alternatively, their activity is actively decorrelated...

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..Highly activated voxels also displayed good reproducibility between trials. On average, the BOLD amplitude response to a short 3-s visual stimulus was close to 2%...

..g., ventricles vs. surrounding tissue)...

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..However, experiments with parametric variation of dot motion coherence suggested that segmentation mechanisms based on detection of collinearity can also influence perceptual selection and suppression in binocular rivalry...

..We consider the choice of imaging paradigm as a key component in optimizing the fMRI of the monkey auditory cortex...

..The data therefore suggest that the sensorimotor strategies underlying bimodal speech perception may have a homologous counterpart in a closely related primate ancestor...

..Our findings highlight the power of combined analysis of field potentials and spiking activity for mapping structure to computational function in the brain...

..The quality of the obtained results paves the way for further neuroscientific research, including studies on the cortical microcircuits and the dynamic longitudinal changes occurring during cortical reorganization and plasticity...

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..Electrophysiology experiments corroborated the fMRI results. This indicates that adult macaque V1 has limited potential for reorganization in the months following retinal injury...

..Concentration ratios of white matter versus gray matter tissue as well as between metabolites matched those reported in the literature from healthy human brain, demonstrating the consistency and reliability of the procedure...

..Altogether our findings suggest that cross-modal influences in such simple detection tasks are not exclusively mediated by hard-wired sensory integration but rather point to a prominent role for cognitive and attention-like effects...

..Such pathways may contribute to the behavioral phenomenon of blindsight...

..This suggests that low-level accounts for reduced BOLD activation in higher visual areas cannot be completely ruled out based on scrambling data...

..We conclude that perception of TAM follows an analysis of 3-D form that takes approximately 100 msec. This stage of form analysis may be common to both TAM and second-order motion...

..It is anticipated that the techniques presented here will prove useful for alert monkey fMRI at any magnetic field...

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..These experiments show that macaques naturally display the distinguishing characteristics of face processing seen in humans and provide the first clear demonstration that holistic information guides scan paths for conspecific faces...

..It can therefore be of great importance for studies requiring accurate fixation of a target, or measurement and study of the subject's oculomotor system...

..One important question raised by the aforementioned investigation is whether the reported correlations also apply to alert subjects...

..These findings demonstrate that stimulus features important for categorization are instantiated in the activity of single units (neurons) in the primate inferior temporal cortex...

..We conclude that fMRI constitutes a complement, not a poor-resolution substitute, to invasive techniques, and that it deserves interpretations that acknowledge its stand as a separate signal...

..These findings indicate that uninterrupted subjective perception of an ambiguous pattern is required for the initiation of the brain-state changes underlying multistable vision...

..This distributed network of areas cuts across both "what" and "where" processing streams, reflecting multiple uses for 3D shape representation in perception, recognition, and action...

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..We specifically highlight perspectives for the use of MS for brain functional studies and drug discovery in nonhuman primates...

..This allows fMRI of areas that normally suffer from artifact and thus more reliable whole-brain studies...

..In conclusion, simultaneous EEG/fMRI acquisition is feasible in the macaque monkey preparation at 4.7 T and holds promise for investigating the neural processes that give rise to particular EEG patterns...

..This suggests that V4 plays a key role in resolving indeterminate visual inputs by coordinated interaction between bottom-up and top-down processing streams...

..These results question theories, which suggest that initial fixations are driven by stimulus structure whereas later fixations are determined by informative scene content...

..The exquisite sensitivity of the system and the increased specificity of the hemodynamic signals promise further insights into the relationship of the latter to the underlying physiological activity...

..Consistent with this functional transynaptic spread we also obtained activation in expected projection sites in extrastriate visual areas, demonstrating the utility of our technique in uncovering in vivo functional connectivity maps...

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..Performance of a variety of arrangements of gapped linear arrays was evaluated at 4.7 and 7T in high-resolution anatomical and functional MRI...

..This is especially useful in combined EEG/fMRI experiments, where one can now potentially study neural-hemodynamic relationships across the whole brain volume in a noninvasive manner...

..g., synchronization), not necessarily altering the firing rates of single cells or the LFP power dramatically...

..In addition, they highlight the importance of millisecond-precise neural coding as general functional principle of auditory processing--from the periphery to cortex...

..The findings can now guide neurophysiological recordings in the monkey to expand our understanding of the processing within these fields. Additionally, this work will improve fMRI investigations of the human auditory cortex...

..The NBR was associated with comparable decreases in local field potentials and multiunit activity. Our findings indicate that a significant component of the NBR originates in neuronal activity decreases...

..The results are consistent with a model in which the brain combines information across multiple visual features to resolve ambiguities in visual inputs...

..The choice of optimal stimulus duration represents a trade-off between the spatial specificity and the overhead associated with short stimulus duration...

..Our results demonstrate that humans as well as non-human primates exploit their sensory ability of color vision to achieve higher performance in visual recognition tasks especially when shape features are degraded...

..Here, we discuss the specific challenges and benefits of fMRI in the awake monkey and review the methodologies and strategies for scanning behaving macaques...

..Their co-varying change may be due to feedback from image- to eye-of-origin representations...

..These results extend earlier findings regarding VEP-BOLD coupling and highlight the component- and context-dependency of the relationship between evoked potentials and hemodynamic responses...

..An important factor in overall classification performance is careful preprocessing of the data, including dimensionality reduction, voxel selection and outlier elimination...

..This finding may open up a new dimension in the use and interpretation of EEG in normal and pathological conditions...

..In addition, they propose a role of slow cortical rhythms in stabilizing sensory representations by reducing effects of noise...

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..Similar to human imaging results the update of visual input was enough to activate an extensive network of frontoparietal cortex in the macaque brain, a network which is normally associated with complex cognitive control processes...

..In addition, we found a frequency-dependent spatial pattern of activation. With stimulation protocols and train frequencies used for kindling, the activity strongly spreads ipsilaterally through the hippocampus, DG, subiculum and EC...

..Notably, this very same layer coincided with the largest relaxivity changes as observed in steady-state cerebral blood volume measurements, using the intravascular agent monocrystalline iron oxide nanoparticles (MION)...

..The CBF values in the occipital lobe of the monkey brain quantified with ASL are higher than previously reported in positron emission tomography studies...

..These response biases to looming sounds are consistent with an evolved neural mechanism that processes approaching objects with priority...

..The corrected spectra obtained from the awake monkey afforded the reliable detection of 6-10 cerebral metabolites of 1-ml volumes...

..Together, these findings reveal multisensory modulation of auditory processing prominently in caudal fields but also at the lowest stages of auditory cortical processing...

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..This way, it was possible to acquire high-spatial and high-temporal resolution SE-fMRI data...

..In any case, our results demonstrate that different primate sensory systems rely on common principles for extracting relevant sensory events...

..These findings demonstrates that multisensory integration occurs early and close to primary sensory areas and--because it occurs in anaesthetized animals--suggests that this integration is mediated by preattentive bottom-up mechanisms...

..Only then will we be able to determine whether early cross-modal interactions truly merit the label sensory integration, and how they increase a sensory system's ability to scrutinize its environment and finally aid behavior...

..These findings suggest that unified shape perception in both monkeys and humans involves multiple visual areas that may integrate local elements to global shapes at different spatial scales...

..We conclude that HILIC/MS/MS combined with the push-pull sampling method represents a sensitive technique for simultaneous monitoring of neurotransmitters from EBF samples...

..However, the effect of the PLD on fCBF was smaller than on baseline CBF. These results are of importance for high-resolution applications, and when accurate quantification is required for studies in monkeys as well as in humans...

..The results are discussed in the context of combined fMRI/electrophysiological recordings...

..These neurons thus meet the criteria for sensory integration and provide the auditory modality with multisensory contextual information about co-occurring environmental events...

..We discuss implications of this finding for the interpretation of BOLD activity...

..These observations suggest that the fMRI response to a sensory stimulus for 6% CO2 inhalation occurs in the absence of a hemodynamic response, and it therefore directly reflects oxygen extraction into the tissue...

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