Mapping the visual brain areas susceptible to phosphene induction through brain stimulation.

Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation technique whose effects on neural activity can be uncertain. Within the visual cortex, phosphenes are a useful marker of TMS: They indicate the induction of neural activation that propagates and creates a conscious percept. However, we currently do not know how susceptible different areas of the visual cortex are to TMS-induced phosphenes. In this study, we systematically map out locations in the visual cortex where stimulation triggered phosphenes. We relate this to the retinotopic organization and the location of object- and motion-selective areas, identified by functional magnetic resonance imaging (fMRI) measurements. Our results show that TMS can reliably induce phosphenes in early (V1, V2d, and V2v) and dorsal (V3d and V3a) visual areas close to the interhemispheric cleft. However, phosphenes are less likely in more lateral locations (hMT+/V5 and LOC). This suggests that early and dorsal visual areas are particularly amenable to TMS and that TMS can be used to probe the functional role of these areas.This study was funded by the European Community’s Seventh Framework Programme (FP7/2007-2013) under agreement PITN-GA-2011-290011 and the Welcome Trust (095183/Z/10/Z).This is the final version of the article. It first appeared from Springer via https://doi.org/10.1007/s00221-016-4784-

An innovative technique for the investigation of the 4-fold forbidden beta-decay of 50^{50}V

For the first time a Vanadium-based crystal was operated as cryogenic particle detector. The scintillating low temperature calorimetric technique was used for the characterization of a 22 g YVO$_4$ crystal aiming at the investigation of the 4-fold forbidden non-unique $\beta^-$ decay of $^{50}$V. The excellent bolometric performance of the compound together with high light output of the crystal makes it an outstanding technique for the study of such elusive rate process. The internal radioactive contaminations of the crystal are also investigated showing that an improvement on the current status of material selection and purification are needed, $^{235/238}$U and $^{232}$Th are measured at the level of 28 mBq/kg, 1.3 Bq/kg and 28 mBq/kg, respectively. In this work, we also discuss a future upgrade of the experimental set-up which may pave the road for the detection of the rare $^{50}$V $\beta^-$ decay

The mixed-polarity benefit of stereopsis arises in early visual cortex.

Depth perception is better when observers view stimuli containing a mixture of bright and dark visual features. It is currently unclear where in the visual system sensory processing benefits from the availability of different contrast polarity. To address this question, we applied transcranial magnetic stimulation to the visual cortex to modulate normal neural activity during processing of single- or mixed-polarity random-dot stereograms. In line with previous work, participants gave significantly better depth judgments for mixed-polarity stimuli. Stimulation of early visual cortex (V1/V2) significantly increased this benefit for mixed-polarity stimuli, and it did not affect performance for single-polarity stimuli. Stimulation of disparity responsive areas V3a and LO had no effect on perception. Our findings show that disparity processing in early visual cortex gives rise to the mixed-polarity benefit. This is consistent with computational models of stereopsis at the level of V1 that produce a mixed polarity benefit

Bitcoin Adoption in El Salvador

In September 2021, El Salvador was the first country in the world to adopt Bitcoin as a legal tender, marking the first introduction of a cryptocurrency into a regulated financial system. Using Gross Domestic Product as an indicator for economic growth in El Salvador, it can be estimated how bitcoin adoption affects GDP. The difference in difference design tests the influence of Bitcoin on the treatment group El Salvador whilst controlling for GDP&rsquo;s determinants. The results provide evidence that Bitcoin adoption had a negative impact on GDP, in which El Salvador&rsquo;s GDP decreased 2.22% relative to the control group. </div

Introduction à Musique et danses funéraires

En février 1996, Denise Paulme me remit un épais dossier qu’elle venait de retrouver dans les papiers de son mari André Schaeffner, décédé en 1980, et dont elle destinait la plupart des archives épistolaires, explicitement musicologiques, à la Bibliothèque musicale Gustav Mahler de Paris – dossier sur lequel était écrit de la main de Schaeffner «Mission Dakar-Djibouti et Mission Sahara-Soudan», et qui, outre des coupures de presse, comprenait des correspondances diverses ayant trait à ces deu..

Brain stimulation reveals neural mechanisms of stereopsis

Stereopsis is critical for interaction with our environment. However, binocular disparity in natural images is often ambiguous and this makes it difficult to establish a binocular correspondence solution. In my thesis, I focus on both the challenges of this problem and solutions that the brain applies. To study brain function, I use Transcranial Magnetic Stimulation (TMS) which allows me to causally relate induced changes in neural activity with changes in depth perception. This way I can map out neural mechanisms of stereopsis within the visual cortex. As a first step, I conducted a proof of concept study to confirm where in the visual cortex TMS can be used to study perception. I systematically mapped out where in the visual cortex TMS triggers self-propagating, perceptually noticeable neural activation. I related this to the retinotopic organisation and the location of object- and motion-selective areas, identified by functional Magnetic Resonance Imaging. My work confirms that TMS can trigger perceptually significant neural activation in early and dorsal visual areas. In my second chapter, I investigated how incoherent binocular disparity challenges stereopsis. As disparity coherence is reduced it becomes increasingly challenging to establish global correspondence and consequently observers struggle to perceive depth. Interestingly, this problem is less severe when images contain a mixture of bright and dark features (mixed contrast polarity). By locating where in the brain disparity processing benefits from mixed contrast polarity, I can infer where incoherent disparity might challenge mechanisms of stereopsis. I applied TMS during discrimination of incoherent disparity in images with mixed or single contrast polarity. I found that stimulation over V1 differentially affects perception of mixed and single polarity stimuli. My findings show that mechanisms of stereopsis in early visual cortex process mixed and single polarity differently and suggest these mechanisms are challenged by incoherent disparity. In my final chapter, I investigated the role of parietal cortex in the processing of incoherent disparity information. Findings in both macaque monkeys and human observers suggest that the dorsal visual cortex is particularly involved in the processing of incoherent disparity signals. Here, I tested the role of the posterior parietal cortex in human observers. I used brain stimulation to suppress synaptic transmission in parietal cortex and recorded electroencephalography during incoherent disparity processing. Disrupting parietal cortex caused changes in early, disparity responses in visual cortex. This suggests that parietal cortex provides top-down influence to the visual cortex relevant to incoherent disparity processing.European Commission (FP7, PRISM), Wellcome Trus

Linear Parameter-Varying (LPV) Buckling Control of an Imperfect Beam-Column Subject to Time-Varying Axial Loads

In this paper, active buckling control of an imperfect slender beam-column with circular cross-section by piezo-elastic supports and Linear Parameter-Varying (LPV) control is investigated experimentally. The beam-column is loaded by a time-varying axial compressive load resulting in a lateral deflection of the beam-column due to imperfections. A finite element model of the beam-column under axial load is designed as an LPV system. A reduced and augmented modal model is used to design a quadratically stable gain scheduled LPV control. The control is implemented in an experimental test setup and the maximum bearable loads of the beam-column are obtained. Two cases are tested: with and without LPV control or, respectively, active and passive configuration. With the proposed active LPV buckling control it is possible to compensate the influence of beam-column imperfections and to compensate uncertainty in mounting and loading that in passive configuration without LPV control may lead to early buckling. Eventually, the maximum bearable axial compressive load is increased above the theoretical critical buckling load

Active buckling control of an imperfect beam-column with circular cross-section using piezo-elastic supports and integral LQR control

For slender beam-columns loaded by axial compressive forces, active buckling control provides a possibility to increase the maximum bearable axial load above that of a purely passive structure. In this paper, the potential of active buckling control of an imperfect beam-column with circular cross-section using piezo-elastic supports is investigated numerically. Imperfections are given by an initial deformation of the beam-column caused by a constant imperfection force. With the piezo-elastic supports, active bending moments in arbitrary directions orthogonal to the beam-column's longitudinal axis can be applied at both beam- column's ends. The imperfect beam-column is loaded by a gradually increasing axial compressive force resulting in a lateral deformation of the beam-column. First, a finite element model of the imperfect structure for numerical simulation of the active buckling control is presented. Second, an integral linear-quadratic regulator (LQR) that compensates the deformation via the piezo-elastic supports is derived for a reduced modal model of the ideal beam-column. With the proposed active buckling control it is possible to stabilize the imperfect beam-column in arbitrary lateral direction for axial loads above the theoretical critical buckling load and the maximum bearable load of the passive structure