An MRI-compatible caloric stimulation device for the investigation of human vestibular cortex

Background Self-motion perception involves the integration of vestibular, visual, somatosensory and other sensory cues. The neural responses to caloric vestibular stimulation (CVS) in humans have been investigated with functional magnetic resonance imaging (fMRI). New method We developed an fMRI-compatible, bithermal caloric stimulation device for repeated CVS. Tempered water is pumped via a closed-loop tube-system to one or both ear canals. Water temperature transmits to the surface of the ear canal via a small glass-pod. For our purposes we used hot (47–49 °C), cold (5–7.5 °C), or warm for baseline (30–32.5 °C). The pods are integrated in the MRI ear protection and connected to water influx and efflux tubes. With our device we can apply multiple vestibular stimulation and baseline trials consecutively. Control measurements indicate that the applied temperatures are stable across trials. MRI-signal differences due to water flow and water temperature are restricted to the area surrounding the pod and are unlikely to intrude into brain tissue. Results Vestibular stimulation with our device elicits caloric nystagmus when no central fixation is presented. We validated our system by conducting a CVS experiment during fMRI-scanning. Participants indicated the presence or absence of a self-motion sensation. Periods of self motion yielded activation in the cortical vestibular network including putative human parieto-insular vestibular cortex (PIVC). Comparison with existing methods Our closed-loop device eliminates many problems associated with caloric stimulation during fMRI. Conclusions Our device allows researchers to explore neural responses to CVS and those evoked by combined sensory stimulation

Brain activation during dichoptic presentation of optic flow stimuli

The processing of optic flow fields in motion-sensitive areas in human visual cortex was studied with BOLD (blood oxygen level dependent) contrast in functional magnetic resonance imaging (fMRI). Subjects binocularly viewed optic flow fields in plane (monoptic) or in stereo depth (dichoptic) with various degrees of disparity and increasing radial speed. By varying the directional properties of the stimuli (expansion, spiral motion, random), we explored whether the BOLD effect reflected neuronal responses to these different forms of optic flow. The results suggest that BOLD contrast as assessed by fMRI methods reflects the neural processing of optic flow information in motion-sensitive cortical areas. Furthermore, small but replicable disparity-selective responses were found in parts of Brodmann's area 19

Coherent motion pops out during smooth pursuit

Stimulus motion is a prominent feature that is used by the visual system to segment figure from ground and perceptually bind widely separated objects. Pursuit eye movements can be influenced by such perceptual grouping processes. We have examined the subjects' ability to detect small amounts of coherent motion in random dot kinematograms during pursuit. We compared performance on tests of coherent motion perception while subjects fixated a stationary spot or while they tracked a moving target. The results indicate that smooth pursuit can improve subjects' ability to detect the presence of coherent motion. We tentatively propose that an efference copy of the eye movement signal can enhance the ability of the visual system to detect correlations between sparsely placed targets among noisy distractors

Morphometric analyses of the visual pathways in macular degeneration

Introduction. Macular degeneration (MD) causes central visual field loss. When field defects occur in both eyes and overlap, parts of the visual pathways are no longer stimulated. Previous reports have shown that this affects the grey matter of the primary visual cortex, but possible effects on the preceding visual pathway structures have not been fully established. Method. In this multicentre study, we used high-resolution anatomical magnetic resonance imaging and voxel-based morphometry to investigate the visual pathway structures up to the primary visual cortex of patients with age-related macular degeneration (AMD) and juvenile macular degeneration (JMD). Results. Compared to age-matched healthy controls, in patients with JMD we found volumetric reductions in the optic nerves, the chiasm, the lateral geniculate bodies, the optic radiations and the visual cortex. In patients with AMD we found volumetric reductions in the lateral geniculate bodies, the optic radiations and the visual cortex. An unexpected finding was that AMD, but not JMD, was associated with a reduction in frontal white matter volume. Conclusion. MD is associated with degeneration of structures along the visual pathways. A reduction in frontal white matter volume only present in the AMD patients may constitute a neural correlate of previously reported association between AMD and mild cognitive impairment. Keywords: macular degeneration - visual pathway - visual field - voxel-based morphometryComment: appears in Cortex (2013

fMRI Response During Visual Motion Stimulation in Patients with Late Whiplash Syndrome

After whiplash trauma, up to one fourth of patients develop chronic symptoms including head and neck pain and cognitive disturbances. Resting perfusion single-pho ton-emission computed tomography (SPECT) found decreased temporoparietooccipi tal tracer uptake among these long-term symptomatic patients with late whiplash syn drome. As MT/MST (V5/V5a) are located in that area, this study addressed the question whether these patients show impairments in visual motion perception. We examined five symptomatic patients with late whiplash syndrome, five asymptomatic patients after whiplash trauma, and a control group of seven volunteers without the history of trauma. Tests for visual motion perception and functional magnetic resonance imaging (fMRI) measurements during visual motion stimulation were performed. Symptomatic patients showed a significant reduction in their ability to perceive coherent visual motion com pared with controls, whereas the asymptomatic patients did not show this effect. fMRI activation was similar during random dot motion in all three groups, but was signifi cantly decreased during coherent dot motion in the symptomatic patients compared with the other two groups. Reduced psychophysical motion performance and reduced fMRI responses in symptomatic patients with late whiplash syndrome both point to a functional impairment in cortical areas sensitive to coherent motion. Larger studies are needed to confirm these clinical and functional imaging results to provide a possible additional diagnostic criterion for the evaluation of patients with late whiplash syndrome

A Constrained ICA-EMD Model for Group Level fMRI Analysis

Independent component analysis (ICA), being a data-driven method, has been shown to be a powerful tool for functional magnetic resonance imaging (fMRI) data analysis. One drawback of this multivariate approach is that it is not, in general, compatible with the analysis of group data. Various techniques have been proposed to overcome this limitation of ICA. In this paper, a novel ICA-based workflow for extracting resting-state networks from fMRI group studies is proposed. An empirical mode decomposition (EMD) is used, in a data-driven manner, to generate reference signals that can be incorporated into a constrained version of ICA (cICA), thereby eliminating the inherent ambiguities of ICA. The results of the proposed workflow are then compared to those obtained by a widely used group ICA approach for fMRI analysis. In this study, we demonstrate that intrinsic modes, extracted by EMD, are suitable to serve as references for cICA. This approach yields typical resting-state patterns that are consistent over subjects. By introducing these reference signals into the ICA, our processing pipeline yields comparable activity patterns across subjects in a mathematically transparent manner. Our approach provides a user-friendly tool to adjust the trade-off between a high similarity across subjects and preserving individual subject features of the independent components

Experimentelle Überprüfung einer evolutionstheoretischen Erklärung von Schlafplatzpräferenzen des Menschen

Obwohl Menschen einen großen Teil des Tages an ihrem Schlafplatz verbringen, gibt es kaum experimentelle und theoriegeleitete Studien zur Schlafplatzwahl des Menschen. Da der Mensch im Schlaf relativ schutzlos gegenüber Angreifern ist und eine passende Wahl der Schlafumgebung Schutz und damit höhere Überlebenschancen bietet, wird die Schlafplatzwahl aus evolutionärer Perspektive untersucht. Es wird ein Evolutionsbedingter Psychologischer Mechanismus (EPM) zur Schlafplatzwahl postuliert und daraus abgeleitete Hypothesen überprüft: Ein Schlafplatz sollte so gewählt werden, dass er schnelle Reaktionen auf Angreifer ermöglicht. Daher sollte (1) vom Bett aus die Tür im Blickfeld sein, (2) das Bett in deutlicher Weise von der Tür abgerückt sein und (3) bevorzugt in die Zimmerhälfte gestellt werden, in die sich die Tür öffnet. Eine Studie mit 138 Probanden, die Möbel auf experimentell manipulierten Grundrissen anrichten, kann diese Hypothesen bestätigen

Functional magnetic resonance imaging evidence for binocular interactions in human visual cortex

Using functional magnetic resonance imaging (fMRI), we explored the binocular interactions occurring when subjects viewed dichoptically presented checkerboard stimuli. A flickering radial checkerboard was presented to each eye of the subject, while T2*-weighted images were acquired over the visual cortex with gradient-echo, echoplanar sequences. We compared responses in striate and extrastriate visual cortex under four conditions: both eyes were stimulated at the same time (binocular condition), each eye was stimulated in alternation (monocular condition) or first the one eye then the other eye was stimulated (left eye first - right eye trailing, or vice versa). The results indicate that only the striate area, in and near the calcarine fissure, shows significant differences for these stimulation conditions. These differences are not evident in more remote extrastriate or associational visual areas, although the BOLD response in the stimulation-rest comparison was robust. These results suggest that the effect could be related to inhibitory interactions across ocular dominance columns in striate visual cortex