A molecular line and infrared study of NGC 2264 IRS1

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

Detection of interstellar CH3

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

ISO Spectroscopy of Young Stellar Objects

Observations of gas-phase and solid-state species toward young stellar objects (YSOs) with the spectrometers on board the Infrared Space Observatory are reviewed. The excitation and abundances of the atoms and molecules are sensitive to the changing physical conditions during star-formation. In the cold outer envelopes around YSOs, interstellar ices contain a significant fraction of the heavy element abundances, in particular oxygen. Different ice phases can be distinguished, and evidence is found for heating and segregation of the ices in more evolved objects. The inner warm envelopes around YSOs are probed through absorption and emission of gas-phase molecules, including CO, CO_2, CH_4 and H_2O. An overview of the wealth of observations on gas-phase H_2O in star-forming regions is presented. Gas/solid ratios are determined, which provide information on the importance of gas-grain chemistry and high temperature gas-phase reactions. The line ratios of molecules such as H_2, CO and H_2O are powerful probes to constrain the physical parameters of the gas. Together with atomic and ionic lines such as [0 I] 63 µm, [S I] 25 µm and (Si II] 35 µm, they can also be used to distinguish between photon- and shock-heated gas. Finally, spectroscopic data on circumstellar disks around young stars are mentioned. The results are discussed in the context of the physical and chemical evolution of YSOs

Herschel observations of EXtra-Ordinary Sources (HEXOS): The present and future of spectral surveys with Herschel/HIFI

We present initial results from the Herschel GT key program: Herschel observations of EXtra-Ordinary Sources (HEXOS) and outline the promise and potential of spectral surveys with Herschel/HIFI. The HIFI instrument offers unprecedented sensitivity, as well as continuous spectral coverage across the gaps imposed by the atmosphere, opening up a largely unexplored wavelength regime to high-resolution spectroscopy. We show the spectrum of Orion KL between 480 and 560 GHz and from 1.06 to 1.115 THz. From these data, we confirm that HIFI separately measures the dust continuum and spectrally resolves emission lines in Orion KL. Based on this capability we demonstrate that the line contribution to the broad-band continuum in this molecule-rich source is ∼20−40% below 1 THz and declines to a few percent at higher frequencies. We also tentatively identify multiple transitions of HD18O in the spectra. The first detection of this rare isotopologue in the interstellar medium suggests that HDO emission is optically thick in the Orion hot core with HDO/H2O ∼ 0.02. We discuss the implications of this detection for the water D/H ratio in hot cores

Increased dependence of action selection on recent motor history in Parkinson's disease.

Contains fulltext : 80237.pdf (publisher's version ) (Open Access)It is well known that the basal ganglia are involved in switching between movement sequences. Here we test the hypothesis that this contribution is an instance of a more general role of the basal ganglia in selecting actions that deviate from the context defined by the recent motor history, even when there is no sequential structure to learn or implement. We investigated the effect of striatal dopamine depletion [in Parkinson's disease (PD)] on the ability to switch between independent action plans. PD patients with markedly lateralized signs performed a hand laterality judgment task that involved action selection of their most and least affected hand. Trials where patients selected the same (repeat) or the alternative (switch) hand as in a previous trial were compared, and this was done separately for the most and least affected hand. Behaviorally, PD patients showed switch-costs that were specific to the most affected hand and that increased with disease severity. Functional magnetic resonance imaging (fMRI) showed that this behavioral effect was related to the state of the frontostriatal system: as disease severity increased, contributions of the basal ganglia to the selection process and their effective connectivity with the medial frontal cortex (MFC) decreased, whereas involvement of the MFC increased. We conclude that the basal ganglia are important for rapidly switching toward novel motor plans even when there is no sequential structure to learn or implement. The enhanced MFC activity may result either from reduced focusing abilities of the basal ganglia or from compensatory processes

Posture influences motor imagery: An fMRI study

Contains fulltext : 56041.pdf (publisher's version ) (Closed access)Motor imagery is widely used to study cognitive aspects of the neural control of action. However, what is exactly simulated during motor imagery is still a matter of debate. On the one hand, it is conceivable that motor imagery is an embodied cognitive process, involving a simulation of movements of one's own body. The alternative possibility is that, although motor imagery relies on knowledge of the motor processes, it does not entail an actual motor simulation that is influenced by the physical configuration of one's own body. Here we discriminate between these two hypotheses, in the context of an established motor imagery task: laterality judgments of rotated hand drawings. We found that reaction times of hand laterality judgments followed the biomechanical constraints of left or right hand movements. Crucially, the position of subjects' own left and right arm influenced laterality judgments of left and right hands. In neural terms, hand laterality judgments activated a parieto-frontal network. The activity within this network increased with increasing biomechanical complexity of the imagined hand movements, even when the amount of stimulus rotation was identical. Moreover, activity in the intraparietal sulcus was modulated by subjects' own hand position: a larger incongruence in orientation between the subjects' hand and the stimulus hand led to a selective increase in intraparietal activity. Our results indicate that motor imagery generates motor plans that depend on the current configuration of the limbs. This motor plan is calculated by a parieto-frontal network. Within this network, the posterior parietal cortex appears to incorporate proprioceptive information related to the current position of the body into the motor pla