Attention modulates topology and dynamics of auditory sensory gating.

This work challenges the widely accepted model of sensory gating as a preattention inhibitory process by investigating whether attention directed at the second tone (S2) within a paired-click paradigm could affect gating at the cortical level. We utilized magnetoencephalography, magnetic resonance imaging and spatio-temporal source localization to compare the cortical dynamics underlying gating responses across two conditions (passive and attention) in 19 healthy subjects. Source localization results reaffirmed the existence of a fast processing pathway between the prefrontal cortex (PFC) and bilateral superior temporal gyri (STG) that underlies the auditory gating process. STG source dynamics comprised two gating sub-components, Mb1 and Mb2, both of which showed significant gating suppression (>51%). The attention directed to the S2 tone changed the gating network topology by switching the prefrontal generator from a dorsolateral location, which was active in the passive condition (18/19), to a medial location, active in the attention condition (19/19). Enhanced responses to the attended stimulus caused a significant reduction in gating suppression in both STG gating components (>50%). Our results demonstrate that attention not only modulates sensory gating dynamics, but also exerts topological rerouting of information processing within the PFC. The present data, suggesting that the cortical levels of early sensory processing are subject to top-down influences, change the current view of gating as a purely automatic bottom-up process.

Magnetic source localization of early visual mismatch response.

Previous studies have reported a visual analogue of the auditory mismatch negativity (MMN) response that is based on sensory memory. The neural generators and attention dependence of the visual MMN (vMMN) still remain unclear. We used magnetoencephalography (MEG) and spatio-temporal source localization to determine the generators of the sensory-memory-based vMMN response to non-attended deviants. Ten participants were asked to discriminate between odd and even digits presented at the center of the visual field while grating patterns with different spatial frequencies were presented outside the focus of attention. vMMN was calculated as the difference between MEG responses to infrequent gratings in oddball blocks and the same gratings in equiprobable blocks. The peak latency of the vMMN response was between 100 and 160 ms. The neuromagnetic sources of the vMMN localized in the occipital cortex differed from the sources evoked by the equiprobable gratings and were stimulus-dependent. Our results suggest the existence of separate neural systems for pre-attentive memory-based detection of visual change and provide new evidence that the vMMN is feature-specific.

High-resolution EEG analysis of power spectral density maps and coherence networks in a proportional reasoning task.

Proportional reasoning is very important logical skill required in mathematics and science problem solving as well as in everyday life decisions. However, there is a lack of studies on neurophysiological correlates of proportional reasoning. To explore the brain activity of healthy adults while performing a balance scale task, we used high-resolution EEG techniques and graph-theory based connectivity analysis. After unskilled subjects learned how to properly solve the task, their cortical power spectral density (PSD) maps revealed an increased parietal activity in the beta band. This indicated that subjects started to perform calculations. In addition, the number of inter-hemispheric connections decreased after learning, implying a rearrangement of the brain activity. Repeated performance of the task led to the PSD decrease in the beta and gamma bands among parietal and frontal regions along with a synchronization of lower frequencies. These findings suggest that repetition led to a more automatic task performance. Subjects were also divided in two groups according to their scores on the test of logical thinking (TOLT). Although no group differences in the accuracy and reaction times were found, EEG data showed higher activity in the beta and gamma bands for the group that scored better on TOLT. Learning and repetition induced changes in the pattern of functional connectivity were evident for all frequency bands. Overall, the results indicated that higher frequency oscillations in frontal and parietal regions are particularly important for proportional reasoning.

Early dissociation of face and object processing: a magnetoencephalographic study.

The early dissociation in cortical responses to faces and objects was explored with magnetoencephalographic (MEG) recordings and source localization. To control for differences in the low-level stimulus features, which are known to modulate early brain responses, we created a novel set of stimuli so that their combinations did not have any differences in the visual-field location, spatial frequency, or luminance contrast. Differing responses to face and object (flower) stimuli were found at about 100 ms after stimulus onset in the occipital cortex. Our data also confirm that the brain response to a complex visual stimulus is not merely a sum of the responses to its constituent parts; the nonlinearity in the response was largest for meaningful stimuli.

Foetal Radiation Dose During Prophylactic Occlusion Balloon Placement for Morbidly Adherent Placenta.

OBJECTIVE: To assess foetal absorbed radiation dose (FAD) during prophylactic occlusion balloon catheter (POBC) placement before surgery for morbidly adherent placenta (MAP). METHODS: Retrospective cohort study of women with MAP undergoing POBC before surgery. Women were divided into two groups. Group 1 treated between 2008 and 2011, Group 2 between 2012 and 2014 when fluoroscopy pulse rate reduced from 7.5 to 2 pulses per second. Median and interquartile range (IQR) of dose area product (DAP) and FAD were compared using the Mann-U-Whitney test. FAD was calculated using the PCXMC Monte-Carlo calculation. All procedures were performed using the same equipment (Siemens Axiom Artis dTA) by the same experienced interventional radiology team. RESULTS: Thirty-four women underwent POBC. 16 procedures were performed in Group 1 and 18 in Group 2. Median DAP overall was 1025.10 µGym(2) (IQR 532.1-1775.3): Group 1, 1713.25 µGym(2) (IQR 1164.5-2274.5) and Group 2, 660.70 µGym(2) (IQR 440.9-1020.9) (p = 0.027). Median FAD overall was 4.65 mGy (IQR 2.7-8.2): Group 1, 6.25 mGy (IQR 4.4-10.6) and Group 2, 3.05 mGy (IQR 2.0-5.4) (p = 0.031). CONCLUSIONS: FAD during POBC insertion is low overall. The only change between the two groups was in pulsed fluoroscopy rate which resulted in a significant reduction in FAD. This reinforces the importance of implementation of dose reduction techniques.

Keeping our eyes on the eyes: the case of Arcimboldo.

While contemporaries often viewed his reversible composite heads as scherzi (jokes) and modem art connoisseurs as creative masterpieces, Giuseppe Arcimboldo's ingenious paintings served as inspiring stimuli for the present eye-tracking experiment. One group of participants viewed three chosen paintings in an upright, and another in an upside-down, orientation. We compared how participants viewed three selected areas of interest (AOIs) within the painting when these could, and could not, be identified as a face or distinct facial element (eyes and mouth). The obtained results indicate that the participants fixated the parts of the painting which represent faces more in the upright than in the inverted orientation. Furthermore, in the upright orientation the participants focused more on the upper AOls (eyes) than the lower AOIs (mouth). This was not the case for the inverted orientation of two paintings. In conclusion, the face inversion effect occurs even in this artistic context, and the gaze often goes where the eyes are.

Percutaneous thrombin embolization of a pancreatico-duodenal artery pseudoaneurysm after failing of the endovascular treatment.

Pancreatico-duodenal artery (PDA) pseudoaneurysms are rare vascular conditions with high mortality rates after rupture and they are frequently secondary to pancreatitis, surgery, trauma or infection. Due to the high risk of rupture and bleeding, it is mandatory to treat all pseudoaneurysms, regardless of their size or symptomatology. First option of treatment is open surgical repair, but it has high mortality rate, especially in hemodynamically unstable patients. In the recent years, percutaneous ultrasonography (US)- or computed tomography-guided thrombin injection was proposed as an alternative method for treating visceral aneurysms and pseudoaneurysms, but few reports described this therapy in case of peri-pancreatic pseudoaneurysms. We present a rare case of pseudoaneurysm of the PDA in a patient with no previous history of pancreatitis nor major surgery but with an occlusive lesion of the celiac axis. To the best of our knowledge this is the first reported case of PDA pseudoaneurysm successfully treated in emergency by single transabdominal US-guided injection of thrombin after failed attempts of percutaneous catheterization of the feeding vessel of the pseudoaneurysm.

Development of abstract mathematical reasoning: the case of algebra.

Algebra typically represents the students' first encounter with abstract mathematical reasoning and it therefore causes significant difficulties for students who still reason concretely. The aim of the present study was to investigate the developmental trajectory of the students' ability to solve simple algebraic equations. 311 participants between the ages of 13 and 17 were given a computerized test of equation rearrangement. Equations consisted of an unknown and two other elements (numbers or letters), and the operations of multiplication/division. The obtained results showed that younger participants are less accurate and slower in solving equations with letters (symbols) than those with numbers. This difference disappeared for older participants (16-17 years), suggesting that they had reached an abstract reasoning level, at least for this simple task. A corresponding conclusion arises from the analysis of their strategies which suggests that younger participants mostly used concrete strategies such as inserting numbers, while older participants typically used more abstract, rule-based strategies. These results indicate that the development of algebraic thinking is a process which unfolds over a long period of time. In agreement with previous research, we can conclude that, on average, children at the age of 15-16 transition from using concrete to abstract strategies while solving the algebra problems addressed within the present study. A better understanding of the timing and speed of students' transition from concrete arithmetic reasoning to abstract algebraic reasoning might help in designing better curricula and teaching materials that would ease that transition.

Face activated neurodynamic cortical networks.

Previous neuroimaging studies have shown that complex visual stimuli, such as faces, activate multiple brain regions, yet little is known on the dynamics and complexity of the activated cortical networks during the entire measurable evoked response. In this study, we used simulated and face-evoked empirical MEG data from an oddball study to investigate the feasibility of accurate, efficient, and reliable spatio-temporal tracking of cortical pathways over prolonged time intervals. We applied a data-driven, semiautomated approach to spatio-temporal source localization with no prior assumptions on active cortical regions to explore non-invasively face-processing dynamics and their modulation by task. Simulations demonstrated that the use of multi-start downhill simplex and data-driven selections of time intervals submitted to the Calibrated Start Spatio-Temporal (CSST) algorithm resulted in improved accuracy of the source localization and the estimation of the onset of their activity. Locations and dynamics of the identified sources indicated a distributed cortical network involved in face processing whose complexity was task dependent. This MEG study provided the first non-invasive demonstration, agreeing with intracranial recordings, of an early onset of the activity in the fusiform face gyrus (FFG), and that frontal activation preceded parietal for responses elicited by target faces.

Fast face recognition: eye blink as a reliable behavioral response.

To investigate how quickly we can recognize faces, we used the onset of eye blinking as a behavioral response. The mean reaction time for the blink response was 188±38ms which was 80ms faster than the motor response. As expected, the subjects were more correct and faster to distinguish between faces and houses than when responding to particular face emotion and identity. Our results suggested that early visual processing before 150ms is very important in face processing. This corroborates previous reports from EEG/MEG studies and intracranial recordings on the face-related response around 100ms after stimulus onset. Our findings indicated that blinking can be used as a fast and reliable behavioral response.

Size matters: MEG empirical and simulation study on source localization of the earliest visual activity in the occipital cortex.

While the relationship between sensory stimulation and tasks and the size of the cortical activations is generally unknown, the visual modality offers a unique possibility of an experimental manipulation of stimulus size-related increases of the spatial extent of cortical activation even during the earliest activity in the retinotopically organized primary visual cortex. We used magnetoecephalography (MEG), visual stimuli of increasing size, and numerical simulations on realistic cortical surfaces to explore the effects of increasing spatial extent of the activated cortical sources on the neuromagnetic fields, location estimation biases, and source resolution. Source localization was performed assuming multiple dipoles in a sphere model using an efficient, automatically restarted multi-start simplex minimizer within the Calibrated Start Spatio-Temporal (CSST) algorithm. We found size-related effects on amplitude and latencies and differences in relative locations of the earliest occipital sources evoked by stimuli of increasing size presented at the same eccentricity. This finding was confirmed by single patch simulations. Additionally, simulations of multiple extended sources demonstrated size-related increase in limits in source resolution for bilaterally simulated sources, biases in location estimates for a given separation of sources, and limits in source resolution due to source multiplicity within a hemisphere.

Early cortical responses are sensitive to changes in face stimuli.

Face-related processing has been demonstrated already in the early evoked response around 100 ms after stimulus. The aims of this study were to explore these early responses both at sensor and cortical source level and to explore to what extent they might be modulated by a change in face stimulus. Magnetoencephalographic (MEG) recordings, a visual oddball paradigm, and a semiautomated spatiotemporal source localization method were used to investigate cortical responses to changes in face stimuli. Upright and inverted faces were presented in an oddball paradigm with four conditions; standards and deviants differing in emotion or identity. The task in all conditions was silent counting of the target face with glasses. Deviant face stimuli elicited larger MEG responses at about 100 ms than standard ones did but only for upright faces. Spatiotemporal source localization up to 140 ms after stimulus revealed activation of parietal and temporal sources in addition to occipital ones, all of which demonstrated differences in locations and dynamics for standards, deviants, and targets. Peak latencies of the identified cortical sources were shorter for deviants than standards, again only for upright faces. Our results showed differences in cortical responses to standards and deviants that were more pronounced for upright than for inverted faces, suggesting early detection of face-related changes in visual stimulation. The observed effect provides new evidence for the face sensitivity of the early neuromagnetic response around 100 ms.

Neurodynamic studies on emotional and inverted faces in an oddball paradigm.

The detection of a change in a face stimulus was studied in an oddball paradigm. Event-related potentials (ERPs) and MEG responses to face stimuli were recorded in four conditions: 1) happy standard, neutral deviant; 2) neutral standard, neutral deviant; 3) inverted happy standard, inverted neutral deviant; 4) inverted neutral standard, inverted neutral deviant. In all conditions, the target was a face with glasses. Neutral deviants elicited a negative deflection (with a maximum around 280 ms) in ERP and MEG responses, an effect similar to auditory mismatch negativity. Face inversion diminished deviance-related negativity, implying an important role of face recognition in the observed effect. Emotional content and larger physical differences between stimuli in conditions 1 and 3 compared to conditions 2 and 4 did not show statistically significant effect on the neutral-deviant-related negativity.