Functional Source Imaging Research Articles

Cortical sources of Vernier acuity in the human visual system: An EEG-source imaging study.

Vernier acuity determines the relative position of visual features with a precision better than the sampling resolution of cone receptors in the retina. Because Vernier displacement is thought to be mediated by orientation-tuned mechanisms, Vernier acuity is presumed to be processed in striate visual cortex (V1). However, there is considerable evidence suggesting that Vernier acuity is dependent not only on structures in V1 but also on processing in extrastriate cortical regions. Here we used functional magnetic resonance imaging–informed electroencephalogram source imaging to localize the cortical sources of Vernier acuity in observers with normal vision. We measured suprathreshold and near-threshold responses to Vernier onset/offset stimuli at different stages of the visual cortical hierarchy, including V1, hV4, lateral occipital cortex (LOC), and middle temporal cortex (hMT+). These responses were compared with responses to grating on/off stimuli, as well as to stimuli that control for lateral motion in the Vernier task. Our results show that all visual cortical regions of interest (ROIs) responded to both suprathreshold Vernier and grating stimuli. However, thresholds for Vernier displacement (Vernier acuity) were lowest in V1 and LOC compared with hV4 and hMT+, whereas all visual ROIs had identical thresholds for spatial frequency (grating acuity) and for relative motion. The cortical selectivity of sensitivity to Vernier displacement provides strong evidence that LOC, in addition to V1, is involved in Vernier acuity processing. The robust activation of LOC might be related to the sensitivity to the relative position of features, which is common to Vernier displacement and to some kinds of texture segmentation.

Concept of epilepsy surgery and presurgical evaluation.

Epilepsy surgery is a well-accepted treatment for drug-resistant epilepsy. The success of the epilepsy surgery depends upon an appropriate presurgical evaluation process which should ensure the selection of suitable patients who are likely to become seizure-free following surgery without any unacceptable deficit. The two basic goals of the presurgical evaluation are the accurate localization and delineation of the extent of the epileptogenic zone, and its complete and safe resection. The process of the presurgical evaluation requires a multimodality approach wherein each modality provides unique and complimentary information which is combined with the information provided by other modalities to generate a hypothesis with regard to the likely epileptogenic zone. The basic modalities for the presurgical evaluation are clinical history, long-term video-EEG recording, high-resolution MRI, and neuropsychological evaluation. The additional modalities include functional imaging studies, electrical and magnetic source imaging, functional MRI, and intracranial monitoring. Each modality has its own limitations and the information provided by none of them is absolute. Hence, a concordance among the different modalities is the key to surgical success. The presurgical evaluation is a step-wise process starting form the most basic and most reliable tests and progressing to more complex and invasive modalities. The number of tests required varies according to the complexity involved and may include very basic minimum investigations in a given case, to the use of all the available investigations in more complex cases. The proper selection of various investigations and their accurate interpretation at each stage is required to ensure a successful outcome. In this article, we intend to review some of these basic concepts of presurgical evaluation and epilepsy surgery, and try to provide a frame work of the presurgical evaluation process.

Subject Index

NEXT ARTICLEAbstracts of Presentations at the International Conference on Basic and Clinical Multimodal Imaging (BaCI), a Joint Conference of the International Society for Neuroimaging in Psychiatry (ISNIP), the International Society for Functional Source Imaging (ISFSI), the International Society for Bioelectromagnetism (ISBEM), the International Society for Brain Electromagnetic Topography (ISBET), and the EEG and Clinical Neuroscience Society (ECNS), in Geneva, Switzerland, September 5-8, 2013

Abstracts of Presentations at the International Conference on Basic and Clinical Multimodal Imaging (BaCI), a Joint Conference of the International Society for Neuroimaging in Psychiatry (ISNIP), the International Society for Functional Source Imaging (ISFSI), the International Society for Bioelectromagnetism (ISBEM), the International Society for Brain Electromagnetic Topography (ISBET), and the EEG and Clinical Neuroscience Society (ECNS), in Geneva, Switzerland, September

Abstracts of Presentations at the International Conference on Basic and Clinical Multimodal Imaging (BaCI), a Joint Conference of the International Society for Neuroimaging in Psychiatry (ISNIP), the International Society for Functional Source Imaging (ISFSI), the International Society for Bioelectromagnetism (ISBEM), the International Society for Brain Electromagnetic Topography (ISBET), and the EEG and Clinical Neuroscience Society (ECNS), in Geneva, Switzerland, September

Neuronal networks in children with continuous spikes and waves during slow sleep

Sir, We read with great interest the paper by Siniatchkin et al. (2010), in which they report the results of electroencephalogram (EEG) combined with functional MRI studies performed in children with epileptic encephalopathies with continuous spike-waves during sleep (CSWS). This paper undoubtedly brings novel and valuable data on the pathophysiology of epileptic encephalopathies with CSWS, pointing out the implication of subcortical structures such as the striatum and the thalamus in these disorders. This study actually supports the hypothesis that the neurological regression in CSWS is not only related to the neurophysiological impairment at the site of the epileptic focus but also to epilepsy-induced changes in distant and connected brain areas with a particular involvement of the default mode network (De Tiege et al. , 2009). Nevertheless, we would like to address some limitations regarding the methodology used in this work. The EEG-functional MRI methodology enhances the statistical model used for functional MRI data analysis thanks to various EEG features such as timing, duration, amplitude, morphology and topography of the epileptic activity. In preliminary analyses, Siniatchkin et al. (2010) found a poor correlation between functional MRI results and electrical source imaging results obtained after averaging all …

Phase delays within visual cortex shape the response to steady-state visual stimulation

Although the spatial organization of visual areas can be revealed by functional Magnetic Resonance Imaging (fMRI), the synoptic, non-invasive access to the temporal characteristics of the information flow amongst distributed visual processes remains a technical and methodological challenge. Using frequency-encoded steady-state visual stimulation together with a combination of time-resolved functional magnetic source imaging from magnetoencephalography (MEG) and anatomical magnetic resonance imaging (MRI), this study evidences maps of visuotopic sustained oscillatory neural responses distributed across the visual cortex. Our results further reveal relative phase delays across responding striate and extra-striate visual areas, which thereby shape the chronometry of neural processes amongst these regions. The methodology developed in this study points at further developments in time-resolved analyses of distributed visual processes in the millisecond range, and to new ways of exploring the dynamics of functional processes within the human visual cortex non-invasively.

From the Analysis of the Brain Images to the Study of Brain Networks Using Functional Connectivity and Multimodal Brain Signals

This special issue is entitled ‘‘Cortical network analysis with neuroelectromagnetic and hemodynamic signals.’’ This peer-reviewed special issue is the product of a 2-day workshop held at the University of Rome Sapienza in May 2009, during the bi-annual joint conference of two international scientific societies: The International Society for Bioelectromagnetism (ISBEM) and the International Society for Non-invasive Functional Source Imaging (NIFSI). We are grateful for the support of the European Union, through the COST Action BM0601 ‘‘NeuroMath’’. These two scientific societies are very active, organizing periodic conferences during which the state of the art in the area of estimation of brain activity and connectivity is presented and discussed. The next joint conference of these two societies will be held in Banff, Canada in May 2011.

Use of group theory in the selection and description of regularization methods for functional source imaging

Commonly, functional source imaging problems are "partial" rather than "ordinary" inverse problems--wherein the defining operator consists of component operators that individually do not address all variables of the unknown. When this ordinary-to-partial transition is minimally constrained, algebraic principles can be used to derive a favored methodology--which we do here. The resulting Isotropy method is compared to two other regularization methods proposed for functional source imaging (Kalman and Joint Regularization). This theoretical support for the favored status of the Isotropy method is consistent with its favorable computational performance in low prior information settings, as indicated in recent publications.

Editorial: Functional Source Imaging

Editorial: Functional Source Imaging

Functional cortical source imaging from simultaneously recorded ERP and fMRI

Feasibility of continuously and simultaneously recording visual evoked potentials (VEPs) with fMRI was assessed by quantitatively comparing cortical source images by means of receiver operating characteristic (ROC) curve analysis. The averaged EEG source images coincided well with simultaneously acquired fMRI activations. Strong correlation was found between the cortical source images of VEPs recorded inside and outside the scanner. Application of fMRI prior information strengthened correlation between estimated source images as well as resulted in source estimates with higher spatial resolution. The present results demonstrate that reliable cortical source images can be acquired during simultaneous fMRI scanning and they may be used for multimodal functional source imaging studies.

Special issue on functional source imaging

Special issue on functional source imaging

Special issue on functional source imaging

Special issue on functional source imaging

The Joint Meeting of 5th International Conference on Bioelectromagnetism and 5th International Symposium on Noninvasive Functional Source Imaging within the Human Brain and Heart - May 12-15, 2005 - Call for Papers

The Joint Meeting of 5th International Conference on Bioelectromagnetism and 5th International Symposium on Noninvasive Functional Source Imaging within the Human Brain and Heart - May 12-15, 2005 - Call for Papers

The Joint meeting of 5th International Conference on Bioelectromagnetism and 5th International Symposium on Noninvasive Functional Source Imaging within the Human Brain and Heart

The Joint meeting of 5th International Conference on Bioelectromagnetism and 5th International Symposium on Noninvasive Functional Source Imaging within the Human Brain and Heart

The Joint meeting of 5th International Conference on Bioelectromagnetism and 5th International Symposium on Noninvasive Functional Source Imaging within the Human Brain and Heart

The Joint meeting of 5th International Conference on Bioelectromagnetism and 5th International Symposium on Noninvasive Functional Source Imaging within the Human Brain and Heart

The Joint Meeting of 5th International Conference on Bioelectromagnetism and 5th International Symposium on Noninvasive Functional Source Imaging within the Human Brain and Heart - Call for Papers - May 12-15, 2005

The Joint Meeting of 5th International Conference on Bioelectromagnetism and 5th International Symposium on Noninvasive Functional Source Imaging within the Human Brain and Heart - Call for Papers - May 12-15, 2005

Advances in magnetic resonance imaging of brain tumours.

Magnetic resonance imaging (MRI) of brain tumours provides excellent anatomical detail of brain tumours and can also reveal the biology, cellular structure and vascular dynamics of a tumour, although the use of such features in routine clinical practice has yet to be realized. In this review the latest advances in MRI of brain tumours are discussed and their clinical applications highlighted. A large international study is underway to develop more powerful methods for automated classification of MR spectra based on the acquisition of large datasets of tumour spectra. Diffusion weighted imaging can help in the distinction between gliomas and abscesses, and perfusion weighted imaging can predict response to radiotherapy in low grade gliomas as well as distinguishing between different types of cerebral metastases. Intraoperative MRI has now been shown to be technically feasible, safe and effective in obtaining histological information as well as increasing the likelihood of complete resection for pituitary tumours and gliomas. Functional MRI and magnetic source imaging are alternative modalities that help the surgeon to avoid eloquent brain areas but may occasionally provide misleading information. Diffusion tensor imaging can demonstrate the effect of a tumour on white matter tracts and provides complementary information to that from other techniques that reveal areas of eloquent cortex. Advances in MRI techniques are providing better diagnostic and therapeutic information, but can only ever be a surrogate marker of physiological and pathological processes; until it can routinely be used to image the brain at a cellular level, MRI will always be secondary to pathology in the final diagnostic evaluation.

Efficient Non-Linear 3D Electrical Tomography and Finite Element Optimizations for Functional Source Imaging

Article Efficient Non-Linear 3D Electrical Tomography and Finite Element Optimizations for Functional Source Imaging was published on January 1, 2001 in the journal Biomedical Engineering / Biomedizinische Technik (volume 46, issue s2).

Activation time - a powerful constraint in noninvasive functional source imaging

Activation time - a powerful constraint in noninvasive functional source imaging

Increased auditory cortical representation in musicians.

Acoustic stimuli are processed throughout the auditory projection pathway, including the neocortex, by neurons that are aggregated into 'tonotopic' maps according to their specific frequency tunings. Research on animals has shown that tonotopic representations are not statically fixed in the adult organism but can reorganize after damage to the cochlea or after training the intact subject to discriminate between auditory stimuli. Here we used functional magnetic source imaging (single dipole model) to measure cortical representations in highly skilled musicians. Dipole moments for piano tones, but not for pure tones of similar fundamental frequency (matched in loudness), were found to be enlarged by about 25% in musicians compared with control subjects who had never played an instrument. Enlargement was correlated with the age at which musicians began to practise and did not differ between musicians with absolute or relative pitch. These results, when interpreted with evidence for modified somatosensory representations of the fingering digits in skilled violinists, suggest that use-dependent functional reorganization extends across the sensory cortices to reflect the pattern of sensory input processed by the subject during development of musical skill.