Gavin K. Paterson

Alpha-Band Rhythms in Visual Task Performance: Phase-Locking by Rhythmic Sensory Stimulation

Oscillations are an important aspect of neuronal activity. Interestingly, oscillatory patterns are also observed in behaviour, such as in visual performance measures after the presentation of a brief sensory event in the visual or another modality. These oscillations in visual performance cycle at the typical frequencies of brain rhythms, suggesting that perception may be closely linked to brain oscillations. We here investigated this link for a prominent rhythm of the visual system (the alpha-rhythm, 8–12 Hz) by applying rhythmic visual stimulation at alpha-frequency (10.6 Hz), known to lead to a resonance response in visual areas, and testing its effects on subsequent visual target discrimination. Our data show that rhythmic visual stimulation at 10.6 Hz: 1) has specific behavioral consequences, relative to stimulation at control frequencies (3.9 Hz, 7.1 Hz, 14.2 Hz), and 2) leads to alpha-band oscillations in visual performance measures, that 3) correlate in precise frequency across individuals with resting alpha-rhythms recorded over parieto-occipital areas. The most parsimonious explanation for these three findings is entrainment (phase-locking) of ongoing perceptually relevant alpha-band brain oscillations by rhythmic sensory events. These findings are in line with occipital alpha-oscillations underlying periodicity in visual performance, and suggest that rhythmic stimulation at frequencies of intrinsic brain-rhythms can be used to reveal influences of these rhythms on task performance to study their functional roles.

Dissociated α-Band Modulations in the Dorsal and Ventral Visual Pathways in Visuospatial Attention and Perception

Modulations of occipito-parietal α-band (8-14 Hz) power that are opposite in direction (α-enhancement vs. α-suppression) and origin of generation (ipsilateral vs. contralateral to the locus of attention) are a robust correlate of anticipatory visuospatial attention. Yet, the neural generators of these α-band modulations, their interdependence across homotopic areas, and their respective contribution to subsequent perception remain unclear. To shed light on these questions, we employed magnetoencephalography, while human volunteers performed a spatially cued detection task. Replicating previous findings, we found α-power enhancement ipsilateral to the attended hemifield and contralateral α-suppression over occipito-parietal sensors. Source localization (beamforming) analysis showed that α-enhancement and suppression were generated in 2 distinct brain regions, located in the dorsal and ventral visual streams, respectively. Moreover, α-enhancement and suppression showed different dynamics and contribution to perception. In contrast to the initial and transient dorsal α-enhancement, α-suppression in ventro-lateral occipital cortex was sustained and influenced subsequent target detection. This anticipatory biasing of ventro-lateral extrastriate α-activity probably reflects increased receptivity in the brain region specialized in processing upcoming target features. Our results add to current models on the role of α-oscillations in attention orienting by showing that α-enhancement and suppression can be dissociated in time, space, and perceptual relevance.

PclA, a pneumococcal collagen-like protein with selected strain distribution, contributes to adherence and invasion of host cells

Analysis of Streptococcus pneumoniae sequenced genomes revealed a region present only in selected strains consisting of two ORFs: a putative cell wall anchored protein and a putative transcriptional regulator. The cell wall anchored protein contains large regions of collagen-like repeats, the number of which varies between strains. We have therefore named this protein PclA for pneumococcal collagen-like protein A. The second gene, spr1404, encodes a putative transcriptional regulator. We examined the strain distribution of these two genes among a collection of clinical isolates from invasive pneumococcal disease and found them to be present in 39% of the strains examined. Strains were either positive for both genes or lacked both, with the two genes always present together in the same location of the genome. RT-PCR analysis revealed that pclA is transcribed in vitro, even in the absence of spr1404. Single deletion mutants lacking either gene were not attenuated in a mouse model of invasive pneumonia. However, the pclA mutant was defective in adherence and invasion of host cells in vitro.

Investigating Causality Between Interacting Brain Areas with Multivariate Autoregressive Models of MEG Sensor Data

In this work, we investigate the feasibility to estimating causal interactions between brain regions based on multivariate autoregressive models (MAR models) fitted to magnetoencephalographic (MEG) sensor measurements. We first demonstrate the theoretical feasibility of estimating source level causal interactions after projection of the sensor‐level model coefficients onto the locations of the neural sources. Next, we show with simulated MEG data that causality, as measured by partial directed coherence (PDC), can be correctly reconstructed if the locations of the interacting brain areas are known. We further demonstrate, if a very large number of brain voxels is considered as potential activation sources, that PDC as a measure to reconstruct causal interactions is less accurate. In such case the MAR model coefficients alone contain meaningful causality information. The proposed method overcomes the problems of model nonrobustness and large computation times encountered during causality analysis by existing methods. These methods first project MEG sensor time‐series onto a large number of brain locations after which the MAR model is built on this large number of source‐level time‐series. Instead, through this work, we demonstrate that by building the MAR model on the sensor‐level and then projecting only the MAR coefficients in source space, the true casual pathways are recovered even when a very large number of locations are considered as sources. The main contribution of this work is that by this methodology entire brain causality maps can be efficiently derived without any a priori selection of regions of interest. Hum Brain Mapp, 2013.

Pathogenesis of Streptococcus pneumoniae infections:adaptive immunity, innate immunity, cell biology, virulence factors

During the past two decades the intense study of the infection process of Streptococcus pneumoniae has elucidated multifaceted interactions of the human pathogenic bacterium with the host. A broad spectrum of pneumococcal virulence factors, which are adapted successfully to different host niches, is involved either predominantly in nasopharyngeal colonization or subsequently in dissemination and transmigration of host tissue barriers. The severe course of infections becomes manifest in invasive diseases like pneumonia, meningitis and septicaemia.