Mental Imagery Follows Similar Cortical Reorganization as Perception: Intra-Modal and Cross-Modal Plasticity in Congenitally Blind.

Cortical plasticity in congenitally blind individuals leads to cross-modal activation of the visual cortex and may lead to superior perceptual processing in the intact sensory domains. Although mental imagery is often defined as a quasi-perceptual experience, it is unknown whether it follows similar cortical reorganization as perception in blind individuals. In this study, we show that auditory versus tactile perception evokes similar intra-modal discriminative patterns in congenitally blind compared with sighted participants. These results indicate that cortical plasticity following visual deprivation does not influence broad intra-modal organization of auditory and tactile perception as measured by our task. Furthermore, not only the blind, but also the sighted participants showed cross-modal discriminative patterns for perception modality in the visual cortex. During mental imagery, both groups showed similar decoding accuracies for imagery modality in the intra-modal primary sensory cortices. However, no cross-modal discriminative information for imagery modality was found in early visual cortex of blind participants, in contrast to the sighted participants. We did find evidence of cross-modal activation of higher visual areas in blind participants, including the representation of specific-imagined auditory features in visual area V4.

Outcome of Referrals for Non-Responsive Celiac Disease in a Tertiary Center: Low Incidence of Refractory Celiac Disease in the Netherlands.

OBJECTIVES: Refractory celiac disease (RCD) is a severe cause of non-responsive celiac disease (CD) due to its association with the enteropathy associated T-cell lymphoma (EATL). Conflicting data exist on the prevalence and the clinical manifestations of RCD type I (RCD I) and type II (RCD II). The aim of the current study was to provide insight in the incidence of RCD and in the distinction with other causes of non-responsive CD. METHODS: A total of 106 CD patients were referred to our tertiary referral center between January 2006 and December 2011 for evaluation of non-responsive CD. In addition, a questionnaire was sent to all 82 gastroenterology departments in the Netherlands to reveal whether a patient with RCD was currently being evaluated or had been treated between 2006 and 2012. RESULTS: During a 6 year period, a total of 31 patients were diagnosed with RCD (19 RCD I and 12 RCD II). The nationwide survey revealed 5 additional patients with RCD I and one patient with RCD II. This leads to an annual incidence of RCD of 0.83/10.000 CD patients. The remaining patients were diagnosed with involuntary gluten ingestion (21.7%), delayed mucosal recovery (11.3%), enteropathy associated T-cell lymphoma (7.5%) and autoimmune enteropathy (1.8%). CONCLUSIONS: This nationwide study reveals a low incidence of RCD in the Netherlands. Nevertheless, RCD is a clinically relevant disease entity in CD patients non-responsive to the gluten-free diet.

Clear signals or mixed messages: inter-individual emotion congruency modulates brain activity underlying affective body perception.

The neural basis of emotion perception has mostly been investigated with single face or body stimuli. However, in daily life one may also encounter affective expressions by groups, e.g. an angry mob or an exhilarated concert crowd. In what way is brain activity modulated when several individuals express similar rather than different emotions? We investigated this question using an experimental design in which we presented two stimuli simultaneously, with same or different emotional expressions. We hypothesized that, in the case of two same-emotion stimuli, brain activity would be enhanced, while in the case of two different emotions, one emotion would interfere with the effect of the other. The results showed that the simultaneous perception of different affective body expressions leads to a deactivation of the amygdala and a reduction of cortical activity. It was revealed that the processing of fearful bodies, compared with different-emotion bodies, relied more strongly on saliency and action triggering regions in inferior parietal lobe and insula, while happy bodies drove the occipito-temporal cortex more strongly. We showed that this design could be used to uncover important differences between brain networks underlying fearful and happy emotions. The enhancement of brain activity for unambiguous affective signals expressed by several people simultaneously supports adaptive behaviour in critical situations.

The perception of emotion in body expressions.

During communication, we perceive and express emotional information through many different channels, including facial expressions, prosody, body motion, and posture. Although historically the human body has been perceived primarily as a tool for actions, there is now increased understanding that the body is also an important medium for emotional expression. Indeed, research on emotional body language is rapidly emerging as a new field in cognitive and affective neuroscience. This article reviews how whole-body signals are processed and understood, at the behavioral and neural levels, with specific reference to their role in emotional communication. The first part of this review outlines brain regions and spectrotemporal dynamics underlying perception of isolated neutral and affective bodies, the second part details the contextual effects on body emotion recognition, and final part discusses body processing on a subconscious level. More specifically, research has shown that body expressions as compared with neutral bodies draw upon a larger network of regions responsible for action observation and preparation, emotion processing, body processing, and integrative processes. Results from neurotypical populations and masking paradigms suggest that subconscious processing of affective bodies relies on a specific subset of these regions. Moreover, recent evidence has shown that emotional information from the face, voice, and body all interact, with body motion and posture often highlighting and intensifying the emotion expressed in the face and voice.

Processing of horizontal optic flow in three visual interneurons of the Drosophila brain.

Motion vision is essential for navigating through the environment. Due to its genetic amenability, the fruit fly Drosophila has been serving for a lengthy period as a model organism for studying optomotor behavior as elicited by large-field horizontal motion. However, the neurons underlying the control of this behavior have not been studied in Drosophila so far. Here we report the first whole cell recordings from three cells of the horizontal system (HSN, HSE, and HSS) in the lobula plate of Drosophila. All three HS cells are tuned to large-field horizontal motion in a direction-selective way; they become excited by front-to-back motion and inhibited by back-to-front motion in the ipsilateral field of view. The response properties of HS cells such as contrast and velocity dependence are in accordance with the correlation-type model of motion detection. Neurobiotin injection suggests extensive coupling among ipsilateral HS cells and additional coupling to tangential cells that have their dendrites in the contralateral hemisphere of the brain. This connectivity scheme accounts for the complex layout of their receptive fields and explains their sensitivity both to ipsilateral and to contralateral motion. Thus the main response properties of Drosophila HS cells are strikingly similar to the responses of their counterparts in the blowfly Calliphora, although we found substantial differences with respect to their dendritic structure and connectivity. This long-awaited functional characterization of HS cells in Drosophila provides the basis for the future dissection of optomotor behavior and the underlying neural circuitry by combining genetics, physiology, and behavior.

A zero-gravity instrument to study low velocity collisions of fragile particles at low temperatures.

We discuss the design, operation, and performance of a vacuum setup constructed for use in zero (or reduced) gravity conditions to initiate collisions of fragile millimeter-sized particles at low velocity and temperature. Such particles are typically found in many astronomical settings and in regions of planet formation. The instrument has participated in four parabolic flight campaigns to date, operating for a total of 2.4 h in reduced-gravity conditions and successfully recording over 300 separate collisions of loosely packed dust aggregates and ice samples. The imparted particle velocities achieved range from 0.03 to 0.28 m s(-1) and a high-speed, high-resolution camera captures the events at 107 frames/s from two viewing angles separated by either 48.8 degrees or 60.0 degrees. The particles can be stored inside the experiment vacuum chamber at temperatures of 80-300 K for several uninterrupted hours using a built-in thermal accumulation system. The copper structure allows cooling down to cryogenic temperatures before commencement of the experiments. Throughout the parabolic flight campaigns, add-ons and modifications have been made, illustrating the instrument flexibility in the study of small particle collisions.

Fly motion vision is based on Reichardt detectors regardless of the signal-to-noise ratio.

The computational structure of an optimal motion detector was proposed to depend on the signal-to-noise ratio (SNR) of the stimulus: At low SNR, the optimal motion detector should be a correlation or "Reichardt" type, whereas at high SNR, the detector would employ a gradient scheme [Potters, M. & Bialek, W. (1994) J. Physiol. (Paris) 4, 1755-1775]. Although a large body of experiments supports the Reichardt detector as the processing scheme leading to direction selectivity in fly motion vision, in most of these studies the SNR was rather low. We therefore reinvestigated the question over a much larger SNR range. Using 2-photon microscopy, we found that local dendritic [Ca(2+)] modulations, which are characteristic of Reichardt detectors, occur in response to drifting gratings over a wide range of luminance levels and contrasts. We also explored, as another fingerprint of Reichardt detectors, the dependence of the velocity optimum on the pattern wavelength. Again, we found Reichardt-typical behavior throughout the whole luminance and contrast range tested. Our results, therefore, provide strong evidence that only a single elementary processing scheme is used in fly motion vision.

False-positive results and contamination in nucleic acid amplification assays: suggestions for a prevent and destroy strategy.

Contamination of samples with DNA is still a major problem in microbiology laboratories, despite the wide acceptance of PCR and other amplification techniques for the detection of frequently low amounts of target DNA. This review focuses on the implications of contamination in the diagnosis and research of infectious diseases, possible sources of contaminants, strategies for prevention and destruction, and quality control. Contamination of samples in diagnostic PCR can have far-reaching consequences for patients, as illustrated by several examples in this review. Furthermore, it appears that the (sometimes very unexpected) sources of contaminants are diverse (including water, reagents, disposables, sample carry over, and amplicon), and contaminants can also be introduced by unrelated activities in neighboring laboratories. Therefore, lack of communication between researchers using the same laboratory space can be considered a risk factor. Only a very limited number of multicenter quality control studies have been published so far, but these showed false-positive rates of 9-57%. The overall conclusion is that although nucleic acid amplification assays are basically useful both in research and in the clinic, their accuracy depends on awareness of risk factors and the proper use of procedures for the prevention of nucleic acid contamination. The discussion of prevention and destruction strategies included in this review may serve as a guide to help improve laboratory practices and reduce the number of false-positive amplification results.

Adaptation of response transients in fly motion vision. I: Experiments.

Two types of transient responses have been investigated in fly motion-sensitive neurons in the past: the impulse and the step response. In response to a brief motion pulse, cells show a sudden rise in activity followed by an exponential decay ('impulse response'). In response to the onset of a constant velocity stimulus, cells exhibit transient oscillations before settling to a steady-state value ('step response'). Since the impulse response has been shown to shorten when tested after presentation of an adapting motion stimulus, we investigated whether adaptation also occurs during the step response. We tested this hypothesis by recording extracellularly the response of the H1-cell in the lobula plate of the blowfly Calliphora vicina to gratings of varying pattern contrasts and drift velocity. We found that the transient oscillations of the step response strongly depend on the pattern contrast: at low contrasts, oscillations lasted for several seconds, whereas at high contrasts, they settled within fractions of a second. This suggests that motion adaptation occurs during the initial period of the stimulus presentation and is dependent on the contrast of the motion stimulus. Using identical stimulus parameters (contrast and temporal frequency) for the adapting stimulus and testing the impulse response afterwards, we found that the impulse response and the transient period in the step response shortened in a similar way. We then analyzed the dynamic of the transients oscillations produced by ongoing motion of a square wave pattern in the anti-preferred direction (null direction) of H1. As observed for preferred direction motion, we found that the duration and amplitude of those transients shortened as the contrast and the velocity of the pattern increased, and that the oscillations disappeared when a blank screen instead of a pattern was presented before the onset of motion. Under both stimulus conditions, i.e. grating and blank screen before motion onset, the steady-state response level showed the same dependence on the contrast and temporal frequency of the pattern. When we analyzed the responses of the cell to pattern of various sizes and contrasts moving in the preferred direction of the cell, we found that increments in the size affected the overall amplitude of both the transient oscillations and the steady-state response level, whereas the duration of the oscillations only depended on the local pattern contrast. We also tested the impulse response before and after the presentation of an adapting stimulus presented in either the same or a different location of the visual field. The response shortened only when both the adapting and the test stimuli were presented at the same location. These last experiments demonstrate a strictly local mechanism of adaptation affecting the response transients of both the impulse and the step response.

Use of amplified fragment length polymorphism analysis to identify medically important Candida spp., including C. dubliniensis.

Non-Candida albicans Candida species are increasingly being isolated. These species show differences in levels of resistance to antimycotic agents and mortality. Therefore, it is important to be able to correctly identify the causative organism to the species level. Identification of C. dubliniensis in particular remains problematic due to the high degree of phenotypic similarity between this species and C. albicans. The use of amplified fragment length polymorphism (AFLP) analysis as an identification method for medically important Candida species was investigated. Our results show very clear differences among medically important Candida species. Furthermore, when screening a large collection of clinical isolates previously identified on CHROMagar as C. albicans, we found a misidentification rate of 6%. AFLP analysis is universally applicable, and the patterns can easily be stored in a general, accessible database. Therefore, AFLP might prove to be a reliable method for the identification of medically important Candida species.

Orientation tuning of motion-sensitive neurons shaped by vertical-horizontal network interactions.

We measured the orientation tuning of two neurons of the fly lobula plate (H1 and H2 cells) sensitive to horizontal image motion. Our results show that H1 and H2 cells are sensitive to vertical motion, too. Their response depended on the position of the vertically moving stimuli within their receptive field. Stimulation within the frontal receptive field produced an asymmetric response: upward motion left the H1/H2 spike frequency nearly unaltered while downward motion increased the spike frequency to about 40% of their maximum responses to horizontal motion. In the lateral parts of their receptive fields, no such asymmetry in the responses to vertical image motion was found. Since downward motion is known to be the preferred direction of neurons of the vertical system in the lobula plate, we analyzed possible interactions between vertical system cells and H1 and H2 cells. Depolarizing current injection into the most frontal vertical system cell (VS1) led to an increased spike frequency, hyperpolarizing current injection to a decreased spike frequency in both H1 and H2 cells. Apart from VS1, no other vertical system cell (VS2-8) had any detectable influence on either H1 or H2 cells. The connectivity of VS1 and H1/H2 is also shown to influence the response properties of both centrifugal horizontal cells in the contralateral lobula plate, which are known to be postsynaptic to the H1 and H2 cells. The vCH cell receives additional input from the contralateral VS2-3 cells via the spiking interneuron V1.

Neural networks in the cockpit of the fly.

Flies have been buzzing around on earth for over 300 million years. During this time they have radiated into more than 125,000 different species (Yeates and Wiegmann 1999), so that, by now, roughly every tenth described species is a fly. They thus represent one of the most successful animal groups on our planet. This evolutionary success might, at least in part, be a result of their acrobatic maneuverability, which enables them, for example, to chase mates at turning velocities of more than 3000 degrees s(-1) with delay times of less than 30 ms (Land and Collett 1974; Wagner 1986). It is this fantastic behavior, which has initiated much research during the last decades, both on its sensory control and the biophysical and aerodynamic principles of the flight output (Dickinson et al. 1999, 2000). Here, we review the current state of knowledge about the neural processing of visual motion, which represents one sensory component intimately involved in flight control. Other reviews on this topic have been published with a similar (Hausen 1981, 1984; Hausen and Egelhaaf 1989; Borst 1996) or different emphasis (Frye and Dickinson 2001; Borst and Dickinson 2002). Because of space limitations, we do not review the extensive work that has been done on fly motion-sensitive neurons to advance our understanding of neural coding (Bialek et al. 1991; Rieke et al. 1997; de Ruyter et al. 1997, 2000; Haag and Borst 1997, 1998; Borst and Haag 2001). Unless stated otherwise, all data presented in the following were obtained on the blowfly Calliphora vicina which we will often casually refer to as 'the fly'.

Spatial distribution of low- and high-voltage-activated calcium currents in neurons of the deep cerebellar nuclei.

The spatial distribution of low-voltage-activated (LVA) and high-voltage-activated (HVA) barium currents was investigated in neurons of the deep cerebellar nuclei (DCN) by combining barium imaging with voltage clamp. The current-induced fluorescence signal (DeltaF/F) of the HVA current was five times higher then the LVA-induced signal at the soma, but both signals were approximately equal in size in distant dendrites. This position-dependent shift of DeltaF/F indicates a non-uniform distribution of the underlying calcium channels. The higher weight of the LVA signal in the dendrites suggests that the LVA might be of particular relevance for the dendritic integration of synaptic inputs.

Recurrent network interactions underlying flow-field selectivity of visual interneurons.

Motion-sensitive large-field neurons found at higher processing stages in many species often exhibit a remarkable selectivity for particular flow fields. However, the underlying neural mechanisms are not yet understood. We studied this problem in the so-called lobula plate tangential cells (LPTCs) of the fly. Investigating the connectivity between LPTCs by means of dual recordings, we find two types of connections: (1) heterolateral connections between LPTCs of both hemispheres and (2) ipsilateral connections between LPTCs within one lobula plate. The circuit is suitable to amplify incoming, dendritic signals in the case of rotatory flow fields and to reduce them in the case of other flow-field structures. In addition to feedforward connectivity, thus, the flow-field selectivity of LPTCs may be significantly attributable to recurrent excitation involving the network of large-field neurons in both brain hemispheres.

Detection of Candida spp. in blood cultures using nucleic acid sequence-based amplification (NASBA).

Candida spp. are the main causes of fungal infections in immunocompromised patients. It is known, that the routinely used automated blood culture systems may fail to detect yeasts. We therefore investigated, whether Nucleic Acid Sequence-Based Amplification (NASBA) can be used to improve the detection rate of Candida spp. in blood cultures. Culture-positive as well as negative blood cultures from patients with a proven candidaemia were analyzed, and the results of BacT/Alert monitoring were compared with the results of NASBA-based detection of yeast RNA. With the NASBA-assay, the number of positive blood cultures increased from 21% to 34%. The NASBA-assay may confirm the diagnosis and demonstrate the need for prolonged treatment. In addition it may shorten the time to detection. In summary, using NASBA for the detection of yeast RNA in blood cultures, we have shown for the first time that it is possible to improve the detection rate of yeasts in blood cultures by using amplification technology.

Effects of mean firing on neural information rate.

We investigated the effect of mean firing on the information rate of a spiking motion-sensitive neuron in the fly (H1-cell). In the control condition, the cell was stimulated repeatedly by identical zero-symmetrical white-noise motion. The mean firing rate was manipulated by adding a constant velocity offset either in the same area of the receptive field where the dynamic stimulus was displayed or in a separate one. We determined the information rate in the resulting spike trains in the time domain as the difference between the total and the noise entropy rate and found that the information rate increases with increasing mean firing under both stimulus conditions.

Cholinergic and GABAergic pathways in fly motion vision.

BACKGROUND: The fly visual system is a highly ordered brain structure with well-established physiological and behavioral functions. A large number of interneurons in the posterior part of the third visual neuropil, the lobula plate tangential cells (LPTCs), respond to visual motion stimuli. In these cells the mechanism of motion detection has been studied in great detail. Nevertheless, the cellular computations leading to their directionally selective responses are not yet fully understood. Earlier studies addressed the neuropharmacological basis of the motion response in lobula plate interneurons. In the present study we investigated the distribution of the respective neurotransmitter receptors in the fly visual system, namely nicotinic acetylcholine receptors (nAChRs) and GABA receptors (GABARs) demonstrated by antibody labeling. RESULTS: The medulla shows a laminar distribution of both nAChRs and GABARs. Both receptor types are present in layers that participate in motion processing. The lobula also shows a characteristic layering of immunoreactivity for either receptor in its posterior portion. Furthermore, immunostaining for nAChRs and GABARs can be observed in close vicinity of lobula plate tangential cells. Immunostaining of GABAergic fibers suggests that inhibitory inputs from the medulla are relayed through the lobula to the lobula plate rather than through direct connections between medulla and lobula plate. CONCLUSIONS: The interaction of excitatory and inhibitory pathways is essential for the computation of visual motion responses and discussed in the context of the Reichardt model for motion detection.

Direction selectivity in ganglion cells: pre or post?

Contrary to a recent finding in rabbit retina, Borg-Graham reports that inputs to retinal ganglion neurons in turtles are already directionally selective.

Mechanisms of dendritic calcium signaling in fly neurons.

We examined the mechanisms underlying dendritic calcium accumulation in lobula plate tangential cells of the fly visual system using an in vitro preparation of the fly brain. Local visual stimulation evokes a localized calcium signal in the dendrites of these cells in vivo. Here we show that a similar localized calcium accumulation can be elicited in vitro by focal iontophoretic application of the cholinergic agonist carbachol. The calcium signal had at least two sources: first, voltage-dependent calcium channels contributed to the carbachol-induced signal and were concentrated on the dendrite, the soma, and the terminal ramification of the axon. However, the dendritic calcium signal induced by carbachol stimulation was only weakly dependent on membrane depolarization. The most likely explanation for the second, voltage-independent part of the dendritic calcium signal is calcium entry through nicotinic acetylcholine receptors. We found no indication of second-messenger or calcium-mediated calcium release from intracellular stores. In summary, the characteristic spatiotemporal calcium signals in the dendrites of lobula plate tangential cells can be reproduced in vitro, and result from a combination of voltage- and ligand-gated calcium influx.