A new approach to neuroimaging with magnetoencephalography

We discuss the application of beamforming techniques to the field of magnetoencephalography (MEG). We argue that beamformers have given us an insight into the dynamics of oscillatory changes across the cortex not explored previously with traditional analysis techniques that rely on averaged evoked responses. We review several experiments that have used beamformers, with special emphasis on those in which the results have been compared to those observed in functional magnetic resonance imaging (fMRI) and on those studying induced phenomena. We suggest that the success of the beamformer technique, despite the assumption that there are no linear interactions between the mesoscopic local field potentials across distinct cortical areas, may tell us something of the balance between functional integration and segregation in the human brain. What is more, MEG beamformer analysis facilitates the study of these complex interactions within cortical networks that are involved in both sensory-motor and cognitive processes.     

The missing link: analogous human and primate cortical gamma oscillations

Recent animal studies highlighting the relationship between functional imaging signals and the underlying neuronal activity have revealed the potential capabilities of non-invasive methods. However, the valuable exchange of information between animal and human studies remains restricted by the limited evidence of direct physiological links between species. In this study we used magnetoencephalography (MEG) to investigate the occurrence of 30-70 Hz (gamma) oscillations in human visual cortex, induced by the presentation of visual stimuli of varying contrast. These oscillations, well described in the animal literature, were observed in retinotopically concordant locations of visual cortex and show striking similarity to those found in primate visual cortex using surgically implanted electrodes. The amplitude of the gamma oscillations increases linearly with stimulus contrast in strong correlation with the gamma oscillations found in the local field potential (LFP) of the macaque. We demonstrate that non-invasive magnetic field measurements of gamma oscillations in human visual cortex concur with invasive measures of activation in primate visual cortex, suggesting both a direct representation of underlying neuronal activity and a concurrence between human and primate cortical activity.     

The IFN-beta and retinoic acid-induced cell death regulator GRIM-19 is upregulated during focal cerebral ischemia.

The induction of GRIM-19 has been shown to be essential for interferon-beta (IFN-beta)-induced and retinoic acid (RA)-induced tumor cell death. We have studied the localization and levels of GRIM-19 in IFN/RA-induced cell death in neural cells and in focal cerebral ischemia. Exposure to IFN/RA caused a approximately 15-fold increase in GRIM-19 protein levels and induced >50% cell death in human neuroblastoma SH-SY5Y cells. In rats subjected to permanent focal cerebral ischemia, increased oxidative stress, as well as increased GRIM mRNA levels (32-fold) and increased GRIM-19 (>50%) protein levels were noted in the ipsilateral (affected) hemisphere compared with the contralateral (unaffected) hemisphere. These results suggest that GRIM-19 may play a role in ischemia-induced neuronal cell death.     

Automated MRI parcellation of the frontal lobe

Examination of associations between specific disorders and physical properties of functionally relevant frontal lobe sub‐regions is a fundamental goal in neuropsychiatry. Here, we present and evaluate automated methods of frontal lobe parcellation with the programs FreeSurfer(FS) and TOADS‐CRUISE(T‐C), based on the manual method described in Ranta et al. [2009]: Psychiatry Res 172:147‐154 in which sulcal‐gyral landmarks were used to manually delimit functionally relevant regions within the frontal lobe: i.e., primary motor cortex, anterior cingulate, deep white matter, premotor cortex regions (supplementary motor complex, frontal eye field, and lateral premotor cortex) and prefrontal cortex (PFC) regions (medial PFC, dorsolateral PFC, inferior PFC, lateral orbitofrontal cortex [OFC] and medial OFC). Dice's coefficient, a measure of overlap, and percent volume difference were used to measure the reliability between manual and automated delineations for each frontal lobe region. For FS, mean Dice's coefficient for all regions was 0.75 and percent volume difference was 21.2%. For T‐C the mean Dice's coefficient was 0.77 and the mean percent volume difference for all regions was 20.2%. These results, along with a high degree of agreement between the two automated methods (mean Dice's coefficient = 0.81, percent volume difference = 12.4%) and a proof‐of‐principle group difference analysis that highlights the consistency and sensitivity of the automated methods, indicate that the automated methods are valid techniques for parcellation of the frontal lobe into functionally relevant sub‐regions. Thus, the methodology has the potential to increase efficiency, statistical power and reproducibility for population analyses of neuropsychiatric disorders with hypothesized frontal lobe contributions. Hum Brain Mapp 35:2009–2026, 2014. © 2013 Wiley Periodicals, Inc .     

Psychiatric evaluation in patients with central serous chorioretinopathy in Asian Indians

Purpose:This study aimed at psychiatric evaluation of patients with central serous chorioretinopathy (CSCR) and its association.Material:Consecutive patients diagnosed to have CSCR were included in the study. The participants underwent a routine eye examination. After informed consent, participants were subjected to psychiatric evaluation by a qualified psychiatrist. Details of evaluation and psychiatric disorders were documented and if treatment required were given by the psychiatrist. The outcome measure was the incidence of psychological disorder.Results:Cross-sectional observational data analysis of 40 patients diagnosed to have treatment-naive CSCR who agreed to undergo psychiatric evaluation were included in the study. The ethnic origin of the patients was Asian Indian. The mean age was 39.55 ± 8.33 years with a male to female ratio of 33:7. After a thorough psychiatric evaluation, 31 individuals (77.5%) diagnosed to have mixed anxiety disorders, 4 (10%) had the major depressive disorder, and 5 (12.5%) had adjustment disorder. All 40 patients had stressed personality. All 40 patients had treatment with anti-anxiolytics and advised lifestyle modification. Of these 40 patients, one patient (2.5%) underwent treatment additionally with an antidepressant.Conclusion:All patients with acute CSCR had some form of psychiatric disorder. Psychiatric evaluation in acute treatment naïve CSCR may contribute to the management besides other factors known in the management.     

Intersubject variability and induced gamma in the visual cortex: DCM with empirical Bayes and neural fields

This article describes the first application of a generic (empirical) Bayesian analysis of between‐subject effects in the dynamic causal modeling (DCM) of electrophysiological (MEG) data. It shows that (i) non‐invasive (MEG) data can be used to characterize subject‐specific differences in cortical microcircuitry and (ii) presents a validation of DCM with neural fields that exploits intersubject variability in gamma oscillations. We find that intersubject variability in visually induced gamma responses reflects changes in the excitation‐inhibition balance in a canonical cortical circuit. Crucially, this variability can be explained by subject‐specific differences in intrinsic connections to and from inhibitory interneurons that form a pyramidal‐interneuron gamma network. Our approach uses Bayesian model reduction to evaluate the evidence for (large sets of) nested models—and optimize the corresponding connectivity estimates at the within and between‐subject level. We also consider Bayesian cross‐validation to obtain predictive estimates for gamma‐response phenotypes, using a leave‐one‐out procedure. Hum Brain Mapp 37:4597–4614, 2016. © The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.