Fractal morphology, imaging and mass spectrometry of single aerosol particles in flight

The morphology of micrometre-size particulate matter is of critical importance in fields ranging from toxicology to climate science, yet these properties are surprisingly difficult to measure in the particles' native environment. Electron microscopy requires collection of particles on a substrate; visible light scattering provides insufficient resolution; and X-ray synchrotron studies have been limited to ensembles of particles. Here we demonstrate an in situ method for imaging individual sub-micrometre particles to nanometre resolution in their native environment, using intense, coherent X-ray pulses from the Linac Coherent Light Source free-electron laser. We introduced individual aerosol particles into the pulsed X-ray beam, which is sufficiently intense that diffraction from individual particles can be measured for morphological analysis. At the same time, ion fragments ejected from the beam were analysed using mass spectrometry, to determine the composition of single aerosol particles. Our results show the extent of internal dilation symmetry of individual soot particles subject to non-equilibrium aggregation, and the surprisingly large variability in their fractal dimensions. More broadly, our methods can be extended to resolve both static and dynamic morphology of general ensembles of disordered particles. Such general morphology has implications in topics such as solvent accessibilities in proteins, vibrational energy transfer by the hydrodynamic interaction of amino acids, and large-scale production of nanoscale structures by flame synthesis.

Femtosecond dark-field imaging with an X-ray free electron laser

The emergence of femtosecond diffractive imaging with X-ray lasers has enabled pioneering structural studies of isolated particles, such as viruses, at nanometer length scales. However, the issue of missing low frequency data significantly limits the potential of X-ray lasers to reveal sub-nanometer details of micrometer-sized samples. We have developed a new technique of dark-field coherent diffractive imaging to simultaneously overcome the missing data issue and enable us to harness the unique contrast mechanisms available in dark-field microscopy. Images of airborne particulate matter (soot) up to two microns in length were obtained using single-shot diffraction patterns obtained at the Linac Coherent Light Source, four times the size of objects previously imaged in similar experiments. This technique opens the door to femtosecond diffractive imaging of a wide range of micrometer-sized materials that exhibit irreproducible complexity down to the nanoscale, including airborne particulate matter, small cells, bacteria and gold-labeled biological samples.

Defensive peripersonal space: the blink reflex evoked by hand stimulation is increased when the hand is near the face

Electrical stimulation of the median nerve at the wrist may elicit a blink reflex [hand blink reflex (HBR)] mediated by a neural circuit at brain stem level. As, in a Sherringtonian sense, the blink reflex is a defensive response, in a series of experiments we tested, in healthy volunteers, whether and how the HBR is modulated by the proximity of the stimulated hand to the face. Electromyographic activity was recorded from the orbicularis oculi, bilaterally. We observed that the HBR is enhanced when the stimulated hand is inside the peripersonal space of the face, compared with when it is outside, irrespective of whether the proximity of the hand to the face is manipulated by changing the position of the arm ( experiment 1) or by rotating the head while keeping the arm position constant ( experiment 3). Experiment 2 showed that such HBR enhancement has similar magnitude when the participants have their eyes closed. Experiments 4 and 5 showed, respectively, that the blink reflex elicited by the electrical stimulation of the supraorbital nerve, as well as the N20 wave of the somatosensory evoked potentials elicited by the median nerve stimulation, are entirely unaffected by hand position. Taken together, our results provide compelling evidence that the brain stem circuits mediating the HBR in humans undergo tonic and selective top-down modulation from higher order cortical areas responsible for encoding the location of somatosensory stimuli in external space coordinates. These findings support the existence of a “defensive” peripersonal space, representing a safety margin advantageous for survival.

Bypassing primary sensory cortices--a direct thalamocortical pathway for transmitting salient sensory information

Detection and appropriate reaction to sudden and intense events happening in the sensory environment is crucial for survival. By combining Bayesian model selection with dynamic causal modeling of functional magnetic resonance imaging data, a novel analysis approach that allows inferring the causality between neural activities in different brain areas, we demonstrate that salient sensory information reaches the multimodal cortical areas responsible for its detection directly from the thalamus, without being first processed in primary and secondary sensory-specific areas. This direct thalamocortical transmission of multimodal salient information is parallel to the processing of finer stimulus attributes, which are transmitted in a modality-specific fashion from the thalamus to the relevant primary sensory areas. Such direct thalamocortical connections bypassing primary sensory cortices provide a fast and efficient way for transmitting information from subcortical structures to multimodal cortical areas, to allow the early detection of salient events and, thereby, trigger immediate and appropriate behavior.

MEDI-573 as a novel approach to IGF-1R and IR-A signaling inhibition by blocking IGF ligands: Phase I PK/PD, safety data, and disease linkage studies in breast cancer

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Background: MEDI-573 is a dual-targeting human antibody that neutralizes IGF-I/-II ligands and inhibits IGF-1R and insulin receptor-A (IR-A) signaling pathways, which play a role in breast and other epithelial cancers. By sparing IR-B and its hybrid receptors, MEDI-573 is expected to achieve antitumor activity without perturbing glucose homeostasis.

Methods: In a 3 + 3 dose-escalation trial ( NCT00816361 ), patients with advanced solid tumors, KPS ≥ 60, received MEDI-573 as a weekly 1-hr IV infusion at 0.5, 1.5, 5, 10, or 15 mg/kg every 21 days. Objectives included determination of MTD, safety profile, pharmacokinetics (PK), pharmacodynamics, and tumor response. In a separate biomarker study, mRNA expression of IR-A and IR-B was compared in HR+/HER- breast cancers.

Results: Patients included 13M/12F (17 evaluable for efficacy at data cutoff); median age 59 yrs (range 37-78). No DLTs, drug-related SAEs, or significant toxicity patterns were reported. Forty-five AEs were considered treatment-related (% of patients): decreased appetite (28%), fatigue (24%), nausea (20%), diarrhea (16%), and anemia (12%). Hyperglycemia occurred in 2 patients, 1 with evidence of prestudy insulin resistance. No other significant changes in plasma glucose levels occurred. MEDI-573 had dose-proportionality, with AUC of 415 ± 165, 597 ± 298, and 1940 ± 904 d*μg/mL at 5, 10, and 15 mg/kg, respectively. Suppression of free IGF-1 and -2 was fully achieved at doses ≥ 5 mg/kg. Stable disease spanning ≥ 12 wks (range 12-36+) was seen in 6/17 patients. No antidrug antibodies were reported. In a study to identify breast cancer subsets that are dependent on IGF signaling, the IR-A:IR-B ratio was significantly higher in HR+/HER2- breast cancer than matched adjacent normal tissues and in proliferative luminal B than in luminal A breast cancer.

Conclusions: MEDI-573 showed acceptable safety and favorable PK profiles without significant changes in glucose levels. The IR-A:IR-B ratio supports a biomarker approach for MEDI-573 patient stratification. A biomarker-rich phase Ib/II study of MEDI-573 with an aromatase inhibitor in patients with advanced HR+/HER2- breast cancer opens in 2011.

Taking into account latency, amplitude, and morphology: improved estimation of single-trial ERPs by wavelet filtering and multiple linear regression

Across-trial averaging is a widely used approach to enhance the signal-to-noise ratio (SNR) of event-related potentials (ERPs). However, across-trial variability of ERP latency and amplitude may contain physiologically relevant information that is lost by across-trial averaging. Hence, we aimed to develop a novel method that uses 1) wavelet filtering (WF) to enhance the SNR of ERPs and 2) a multiple linear regression with a dispersion term (MLR(d)) that takes into account shape distortions to estimate the single-trial latency and amplitude of ERP peaks. Using simulated ERP data sets containing different levels of noise, we provide evidence that, compared with other approaches, the proposed WF+MLR(d) method yields the most accurate estimate of single-trial ERP features. When applied to a real laser-evoked potential data set, the WF+MLR(d) approach provides reliable estimation of single-trial latency, amplitude, and morphology of ERPs and thereby allows performing meaningful correlations at single-trial level. We obtained three main findings. First, WF significantly enhances the SNR of single-trial ERPs. Second, MLR(d) effectively captures and measures the variability in the morphology of single-trial ERPs, thus providing an accurate and unbiased estimate of their peak latency and amplitude. Third, intensity of pain perception significantly correlates with the single-trial estimates of N2 and P2 amplitude. These results indicate that WF+MLR(d) can be used to explore the dynamics between different ERP features, behavioral variables, and other neuroimaging measures of brain activity, thus providing new insights into the functional significance of the different brain processes underlying the brain responses to sensory stimuli.

Stimulus Novelty, and Not Neural Refractoriness, Explains the Repetition Suppression of Laser-Evoked Potentials

Brief radiant laser pulses selectively activate skin nociceptors and elicit transient brain responses (laser-evoked potentials [LEPs]). When LEPs are elicited by pairs of stimuli (S1–S2) delivered at different interstimulus intervals (ISIs), the S2-LEP is strongly reduced at short ISIs (250 ms) and progressively recovers at longer ISIs (2,000 ms). This finding has been interpreted in terms of order of arrival of nociceptive volleys and refractoriness of neural generators of LEPs. However, an alternative explanation is the modulation of another experimental factor: the novelty of the eliciting stimulus. To test this alternative hypothesis, we recorded LEPs elicited by pairs of nociceptive stimuli delivered at four ISIs (250, 500, 1,000, 2,000 ms), using two different conditions. In the constant condition, the ISI was identical across the trials of each block, whereas in the variable condition, the ISI was varied randomly across trials and single-stimulus trials were intermixed with paired trials. Therefore the time of occurrence of S2 was both less novel and more predictable in the constant than in the variable condition. In the constant condition, we observed a significant ISI-dependent suppression of the biphasic negative–positive wave (N2–P2) complex of the S2-LEP. In contrast, in the variable condition, the S2-LEP was completely unaffected by stimulus repetition. The pain ratings elicited by S2 were not different in the two conditions. These results indicate that the repetition-suppression of the S2-LEP is not due to refractoriness in nociceptive afferent pathways, but to a modulation of novelty and/or temporal predictability of the eliciting stimulus. This provides further support to the notion that stimulus saliency constitutes a crucial determinant of LEP magnitude and that a significant fraction of the brain activity time-locked to a brief and transient sensory stimulus is not directly related to the quality and the intensity of the corresponding sensation, but to bottom-up attentional processes.

Cryptotomography: reconstructing 3D Fourier intensities from randomly oriented single-shot diffraction patterns

We reconstructed the 3D Fourier intensity distribution of monodisperse prolate nanoparticles using single-shot 2D coherent diffraction patterns collected at DESY's FLASH facility when a bright, coherent, ultrafast x-ray pulse intercepted individual particles of random, unmeasured orientations. This first experimental demonstration of cryptotomography extended the expansion-maximization-compression framework to accommodate unmeasured fluctuations in photon fluence and loss of data due to saturation or background scatter. This work is an important step towards realizing single-shot diffraction imaging of single biomolecules.