Induced and Evoked Properties of Vibrotactile Adaptation in the Primary Somatosensory Cortex.

Prolonged exposure to afferent stimulation ("adaptation") can cause profound short-term changes in the responsiveness of cortical sensory neurons. While several models have been proposed that link adaptation to single-neuron dynamics, including GABAergic inhibition, the process is currently imperfectly understood at the whole-brain level in humans. Here, we used magnetoencephalography (MEG) to examine the neurophysiological correlates of adaptation within SI in humans.

Transcranial modulation of brain oscillatory responses: A concurrent tDCS-MEG investigation.

Despite the increasing use of transcranial direct current stimulation (tDCS), the physiological mechanisms underlying its effects are still largely unknown. One approach to directly investigate the effects of the neuromodulation technique on the brain is to integrate tDCS with non-invasive neuroimaging in humans. To provide new insight into the neurobiology of the method, DC stimulation (1mA, 600s) was applied concurrently with Magnetoencephalography (MEG), while participants engaged in a visuomotor task before, during and after a period of tDCS.

Stimulating somatosensory psychophysics: a double-blind, sham-controlled study of the neurobiological mechanisms of tDCS.

The neuromodulation technique transcranial direct current stimulation (tDCS) is thought to produce its effects on behavior by altering cortical excitability. Although the mechanisms underlying the observed effects are thought to rely on the balance of excitatory and inhibitory neurotransmission, the physiological principles of the technique are not completely understood. In this study, we examine the influence of tDCS on vibrotactile adaptation, using a simple amplitude discrimination paradigm that has been shown to exhibit modifications in performance due to changes in inhibitory neurotransmission.

Current practice in the use of MEGA-PRESS spectroscopy for the detection of GABA.

There is increasing interest in the use of edited proton magnetic resonance spectroscopy for the detection of GABA in the human brain. At a recent meeting held at Cardiff University, a number of spectroscopy groups met to discuss the acquisition, analysis and interpretation of GABA-edited MR spectra. This paper aims to set out the issues discussed at this meeting, reporting areas of consensus around parameters and procedures in the field and highlighting those areas where differences remain.

Subtraction artifacts and frequency (mis-)alignment in J-difference GABA editing.

Purpose: To compare the repeatability of γ-aminobutyric acid (GABA) measurements using J-difference editing, before and after spectral realignment-a technique which has previously been demonstrated to improve the quality of J-difference GABA spectra.

Materials And Methods: We performed in vivo measurements in three brain regions (occipital, sensorimotor, and dorsolateral prefrontal cortex [DLPFC]), and analyzed these using alternative alignment approaches to evaluate the impact of alignment on repeatability: "Independent alignment" (aligning each subspectrum independently) and "Pairwise alignment" (aligning each on and off subspectrum as a pair) were compared.

Results: Pairwise alignment improved the group mean coefficient of variation in all regions; 0.

Test-retest reliability in fMRI: Or how I learned to stop worrying and love the variability.

This paper briefly recounts the details of one of the first studies of whole brain, single subject variability in functional Magnetic Resonance Imaging (fMRI). In this paper I will not attempt to provide an overview of fMRI reliability, but will instead revisit the choices we made in performing our experiment as we did.

Regionally specific human GABA concentration correlates with tactile discrimination thresholds.

The neural mechanisms underlying variability in human sensory perception remain incompletely understood. In particular, few studies have attempted to investigate the relationship between in vivo measurements of neurochemistry and individuals' behavioral performance. Our previous work found a relationship between GABA concentration in the visual cortex and orientation discrimination thresholds (Edden et al.

Integration of sensory and motor representations of single fingers in the human cerebellum.

The cerebellum is thought to play a key role in the integration of sensory and motor events. Little is known, however, about how sensory and motor maps in the cerebellum superimpose. In the present study we investigated the relationship between these two maps for the representation of single fingers.

Between- and within-scanner variability in the CaliBrain study n-back cognitive task.

Psychiatric neuroimaging techniques are likely to improve understanding of the brain in health and disease, but studies tend to be small, based in one imaging centre and of unclear generalisability. Multicentre studies have great appeal but face problems if functional magnetic resonance imaging (fMRI) data from different centres are to be combined. Fourteen healthy volunteers had two brain scans on different days at three scanners.

Diurnal stability of gamma-aminobutyric acid concentration in visual and sensorimotor cortex.

Purpose: To establish the diurnal stability of edited magnetic resonance spectroscopy measurements of gamma-aminobutyric acid (GABA) in visual and sensorimotor regions of the brain.

Materials And Methods: GABA measurements were made in two regions of the brain (an occipital, "visual" region and a "sensorimotor" region centered on the precentral gyrus) using the MEGA-PRESS editing method, scanning eight healthy adults at five timepoints during a single day. GABA concentration was quantified from the ratio of the GABA integral to the unsuppressed water signal.

Loss of imagery phenomenology with intact visuo-spatial task performance: a case of 'blind imagination'.

The capacity for imagery, enabling us to visualise absent items and events, is a ubiquitous feature of our experience. This paper describes the case of a patient, MX, who abruptly lost the ability to generate visual images. He rated himself as experiencing almost no imagery on standard questionnaires, yet performed normally on standard tests of perception, visual imagery and visual memory.

Functional Magnetic Resonance Imaging (fMRI) reproducibility and variance components across visits and scanning sites with a finger tapping task.

Multicentre MRI studies offer great potential to increase study power and flexibility, but it is not yet clear how reproducible the results from multiple centres may be. Here we present results from the multicentre study 'CaliBrain', examining the reproducibility of fMRI data within and between three sites. Fourteen subjects were scanned twice on three 1.

Rhythms of the brain: an examination of mixed mode oscillation approaches to the analysis of neurophysiological data.

In the nervous system many behaviorally relevant dynamical processes are characterized by episodes of complex oscillatory states, whose periodicity may be expressed over multiple temporal and spatial scales. In at least some of these instances the variability in oscillatory amplitude and frequency can be explained in terms of deterministic dynamics, rather than being purely noise-driven. Recently interest has increased in studying the application of mixed-mode oscillations (MMOs) to neurophysiological data.

Spatiotemporal integration of tactile information in human somatosensory cortex.

Background: Our goal was to examine the spatiotemporal integration of tactile information in the hand representation of human primary somatosensory cortex (anterior parietal somatosensory areas 3b and 1), secondary somatosensory cortex (S2), and the parietal ventral area (PV), using high-resolution whole-head magnetoencephalography (MEG). To examine representational overlap and adaptation in bilateral somatosensory cortices, we used an oddball paradigm to characterize the representation of the index finger (D2; deviant stimulus) as a function of the location of the standard stimulus in both right- and left-handed subjects.

Results: We found that responses to deviant stimuli presented in the context of standard stimuli with an interstimulus interval (ISI) of 0.

Gastric fundic distension activates fronto-limbic structures but not primary somatosensory cortex: a functional magnetic resonance imaging study.

Introduction: The brain representation of visceral stimulation bears important similarities to that of somatic stimulation. However, the role of the primary (S1) and secondary (S2) somatosensory cortices in mediating gastric sensation is uncertain.

Materials And Methods: Eighteen healthy, right-handed volunteers (age 32 years+/-6.

Variability in fMRI: a re-examination of inter-session differences.

We revisit a previous study on inter-session variability (McGonigle et al. [2000]: Neuroimage 11:708-734), showing that contrary to one popular interpretation of the original article, inter-session variability is not necessarily high. We also highlight how evaluating variability based on thresholded single-session images alone can be misleading.

Posterior hypothalamic and brainstem activation in hemicrania continua.

Objective: To determine the brain structures involved in mediating the pain of hemicrania continua using positron emission tomography.

Background: Hemicrania continua is a strictly unilateral, continuous headache of moderate intensity, with superimposed exacerbations of severe intensity that are accompanied by trigeminal autonomic features and migrainous symptoms. The syndrome is exquisitely responsive to indomethacin.