Denis Schwartz

Spatiotemporal brain imaging of visual-evoked activity using interleaved EEG and fMRI recordings.

Combined analysis of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) has the potential to provide higher spatiotemporal resolution than either method alone. In some situations, in which the activity of interest cannot be reliably reproduced (e.g., epilepsy, learning, sleep states), accurate combined analysis requires simultaneous acquisition of EEG and fMRI. Simultaneous measurements ensure that the EEG and fMRI recordings reflect the exact same brain activity state. We took advantage of the spatial filtering properties of the bipolar montage to allow recording of very short (125--250 ms) visual-evoked potentials (VEPs) during fMRI. These EEG and fMRI measurements are of sufficient quality to allow source localization of the cortical generators. In addition, our source localization approach provides a combined EEG/fMRI analysis that does not require any manual selection of fMRI activations or placement of source dipoles. The source of the VEP was found to be located in the occipital cortex. Separate analysis of EEG and fMRI data demonstrated good spatial overlap of the observed activated sites. As expected, the combined EEG/fMRI analysis provided better spatiotemporal resolution than either approach alone. The resulting spatiotemporal movie allows for the millisecond-to-millisecond display of changes in cortical activity caused by visual stimulation. These data reveal two peaks in activity corresponding to the N75 and the P100 components. This type of simultaneous acquisition and analysis allows for the accurate characterization of the location and timing of neurophysiological activity in the human brain.

Simultaneous MEG and intracranial EEG recordings during attentive reading

The relationship between neural oscillations recorded at various spatial scales remains poorly understood partly due to an overall dearth of studies utilizing simultaneous measurements. In an effort to study quantitative markers of attention during reading, we performed simultaneous magnetoencephalography (MEG) and intracranial electroencephalography (iEEG) recordings in four epileptic patients. Patients were asked to attend to a specific color when presented with an intermixed series of red words and green words, with words of a given color forming a cohesive story. We analyzed alpha, beta, and gamma band oscillatory responses to the word presentation and compared the strength and spatial organization of those responses in both electrophysiological recordings. Time-frequency analysis of iEEG revealed a network of clear attention-modulated high gamma band (50-150 Hz) power increases and alpha/beta (9-25 Hz) suppressions in response to the words. In addition to analyses at the sensor level, MEG time-frequency analysis was performed at the source level using a sliding window beamformer technique. Strong alpha/beta suppressions were observed in MEG reconstructions, in tandem with iEEG effects. While the MEG counterpart of high gamma band enhancement was difficult to interpret at the sensor level in two patients, MEG time-frequency source reconstruction revealed additional activation patterns in accordance with iEEG results. Importantly, iEEG allowed us to confirm that several sources of gamma band modulation observed with MEG were indeed of cortical origin rather than EMG muscular or ocular artifact.

Simultaneous MEG-intracranial EEG: New insights into the ability of MEG to capture oscillatory modulations in the neocortex and the hippocampus

Epilepsy is, of course, not one disease but rather a huge number of disorders that can present with seizures. In common, they all reflect brain dysfunction. Moreover, they can affect the mind and, of course, behavior. While animals too may suffer from epilepsy, as far as we know, the electrical discharges are less likely to affect the mind and behavior, which is not surprising. While the epileptic seizures themselves are episodic, the mental and behavioral changes continue, in many cases, interictally. The episodic mental and behavioral manifestations are more dramatic, while the interictal ones are easier to study with anatomical and functional studies. The following extended summaries complement those presented in Part 1.

The birth of musical emotion: a depth electrode case study in a human subject with epilepsy.

Intracranial electroencephalography was recorded in an epileptic patient when he was listening to dissonant and consonant chords and to minor and major chords. Changes in dissonance induced event‐related potentials (ERPs) in the auditory areas from 200 ms onward, in the orbito‐frontal cortex (500–1000 ms), and later in the amygdala and anterior cingulate gyrus (1200–1400 ms), suggesting the sequential involvement of these brain structures in implicit emotional judgment of musical dissonance. Changes in musical mode induced ERPs only in the orbito‐frontal cortex (500–1000 ms), emphasizing the implication of this frontal region in emotional judgment of pleasant music.

Simultaneous VEP and fMRI recordings: Comparison between EEG localization and fMRI activation

In this work we present a method for acquiring high qualit) EEG recordings simultaneouly with echo plannr imaging (EPI). We used a bipolar montage with 32 electrodes to reduce the ballistocardiogram noise during simultaneous recordings. We are analpring the wsual evoked potent& to localize the loci of the cortical generators, and to con pare with the functional MRI activations. We are performing the localization using a realistic head model and two anatomically conatrained inverse methods using.

Three-dimensional approach for the simulation of neurosurgical stereotactic act

The stereotactic procedures allow, with the aid of a reference frame supporting an instrument holder, us to define a trajectory to access to a target in a coordinate system recognized by the imaging systems and corresponding to the frame coordinate system. In the field of stereotactic research, a number of major problems in Medical Imaging are encountered: 3-D imaging, multimodal data fusion, 3-D segmentation, PACS, etc. These problems resolved, the design of a computerized application allowing the neurosurgical stereotactic act simulation has its own problems: development of man/computer interface, 2-D and 3-D display tools, validation, integration of computerized application into the clinical environment, etc.