Spatial Attentional Selection Modulates Early Visual Stimulus Processing Independently of Visual Alpha Modulations.

The capacity-limited human brain is constantly confronted with a huge amount of sensory information. Selective attention is needed for biasing neural processing towards relevant information and consequently allows meaningful interaction with the environment. Activity in the alpha-band has been proposed to be related to top-down modulation of neural inhibition and could thus represent a viable candidate to control the priority of stimulus processing. It is, however, unknown whether modulations in the alpha-band directly relate to changes in the sensory gain control of the early visual cortex. Here, we used a spatial cueing paradigm while simultaneously measuring ongoing alpha-band oscillations and steady-state visual evoked potentials (SSVEPs) as a marker of continuous early sensory processing in the human visual cortex. Thereby, the effects of spatial attention for both of these signals and their potential interactions were assessed. As expected, spatial attention modulated both alpha-band and SSVEP responses. However, their modulations were independent of each other and the corresponding activity profiles differed across task demands. Thus, our results challenge the view that modulations of alpha-band activity represent a mechanism that directly alters or controls sensory gain. The potential role of alpha-band oscillations beyond sensory processing will be discussed in light of the present results.

Dynamic gamma frequency feedback coupling between higher and lower order visual cortices underlies perceptual completion in humans.

To perceive a coherent environment, incomplete or overlapping visual forms must be integrated into meaningful coherent percepts, a process referred to as "Gestalt" formation or perceptual completion. Increasing evidence suggests that this process engages oscillatory neuronal activity in a distributed neuronal assembly. A separate line of evidence suggests that Gestalt formation requires top-down feedback from higher order brain regions to early visual cortex. Here we combine magnetoencephalography (MEG) and effective connectivity analysis in the frequency domain to specifically address the effective coupling between sources of oscillatory brain activity during Gestalt formation. We demonstrate that perceptual completion of two-tone "Mooney" faces induces increased gamma frequency band power (55-71Hz) in human early visual, fusiform and parietal cortices. Within this distributed neuronal assembly fusiform and parietal gamma oscillators are coupled by forward and backward connectivity during Mooney face perception, indicating reciprocal influences of gamma activity between these higher order visual brain regions. Critically, gamma band oscillations in early visual cortex are modulated by top-down feedback connectivity from both fusiform and parietal cortices. Thus, we provide a mechanistic account of Gestalt perception in which gamma oscillations in feature sensitive and spatial attention-relevant brain regions reciprocally drive one another and convey global stimulus aspects to local processing units at low levels of the sensory hierarchy by top-down feedback. Our data therefore support the notion of inverse hierarchical processing within the visual system underlying awareness of coherent percepts.

The development of "medical futility": towards a procedural approach based on the role of the medical profession.

UNLABELLED: Over the past 50 years, technical advances have taken place in medicine that have greatly increased the possibilities of life-prolonging intervention. The increased possibilities of intervening have brought along new ethical questions. Not everything that is technically possible is appropriate in a specific case: not everything that could be done should be done. In the 1980s, a new term was coined to indicate a class of inappropriate INTERVENTIONS: "medically futile treatment". A debate followed, with contributions from the USA and several western European countries. A similar debate later took place in Mediterranean countries, although with a different terminology. The purpose of this article is to provide an up-to-date and systematic analysis of the concept of futility, and to draw some conclusions on its operationalisation in medical practice. While the concept of "medical futility" in theory applies to all kinds of medical intervention that might be performed without being medically indicated-things such as certain medical screenings and cosmetic surgery-in practice the literature on "futility" deals only with life-saving and life-sustaining medical interventions. This article deals with this more limited application of the concept of "futility".

Increased biomagnetic activity in the ventral pathway in mild cognitive impairment.

OBJECTIVE: Mild cognitive impairment (MCI) patients represent an intermediary state between healthy aging and dementia. MCI activation profiles, recorded during a memory task, have been studied either through high spatial resolution or high temporal resolution techniques. However, little is known about the benefit of combining both dimensions. Here, we investigate, by means of magnetoencephalography (MEG), whether spatio-temporal profiles of neuromagnetic activity could differentiate between MCI and age-matched elderly participants. METHODS: Taking the advantage of the high temporal resolution and good spatial resolution of MEG, neuromagnetic activity from 15 elderly MCI patients and 20 age-matched controls was recorded during the performance of a modified version of the Sternberg paradigm. RESULTS: Behavioral performance was similar in both groups. A between group analysis revealed that MCI patients showed bilateral higher activity in the ventral pathway, in both the target and the non-target stimuli. A within-group analysis of the target stimuli, indicates a lack of asymmetry through all late latency windows in both groups. CONCLUSIONS: MCI patients showed a compensatory mechanism represented by an increased bilateral activity of the ventral pathway in order to achieve a behavioral performance similar to the control group. SIGNIFICANCE: This spatio-temporal pattern of activity could be another tool to differentiate between healthy aging and MCI patients.

Source distribution of neuromagnetic slow waves and MEG-delta activity in schizophrenic patients.

BACKGROUND: Schizophrenic patients exhibit more activity in the electroencephalographic delta and theta frequency range than do control subjects. Using magnetic source imaging (MSI) our study aimed to explore this phenomenon in the magnetoencephalogram (MEG), the distribution of its sources, and associations between symptom profiles and sources of low-frequency activity in the brain. METHODS: Whole-head MEG recordings were obtained from 28 schizophrenic patients and 20 healthy control subjects during a resting condition. The generators of the focal magnetic slow waves were located employing a single moving dipole model. Distributed or multiple delta and theta sources were captured by the minimum norm estimate. RESULTS: Both localization procedures showed slow wave activity to be enhanced in schizophrenic patients compared with control subjects. Focal slow wave activity differed most between groups in frontotemporal and in posterior regions. Slow wave activity was associated with symptom characteristics in that positive symptoms varied with frontal delta and theta activity. CONCLUSIONS: Results indicate that activity in low-frequency bands in schizophrenic patients exceeds the activity of control subjects in distinct areas, and that this focal clustering of neuromagnetic slow waves may be related to psychopathologic characteristics.

Age-related occipito-temporal hypoactivation during visual search: relationships between mN2pc sources and performance.

Recently, an event-related potential (ERP) study (Lorenzo-López et al., 2008) provided evidence that normal aging significantly delays and attenuates the electrophysiological correlate of the allocation of visuospatial attention (N2pc component) during a feature-detection visual search task. To further explore the effects of normal aging on the N2pc neural sources, neuromagnetic activity during the execution of a visual search task was recorded in healthy young (N=14) and older (N=20) participants by using magnetoencephalography (MEG). The possible relationships between these neural sources and overt performance were explored by assessing the co-variation between the neural N2pc activity and both the task performance and the execution in the Trail Making Test Form A (TMT-A). Results revealed that young participants showed greater activity in occipito-temporal regions than older participants during the mN2pc (magnetic counterpart of the N2pc component) latency range (190-270ms). Moreover, older participants showed reduced relative activation in the right occipito-temporal source of mN2pc. These findings suggest that the previously observed age-related changes in N2pc parameters are associated with a significant hypoactivation of occipito-temporal N2pc sources that is more marked in the right hemisphere.

Orbitofrontal dysfunction related to depressive symptomatology in subjects with borderline personality disorder.

OBJECTIVE: In order to explore the relationships of fronto-limbic dysfunction with the clinical features of borderline personality disorder (BPD), the authors investigated brain electrophysiological activity in BPD patients following stimulation with emotionally arousing images. METHODS: Seventeen non-medicated patients with borderline personality disorder were studied with magneto-encephalography. Regional cortical activities were obtained by minimum norm estimate (MNE) of steady-state visual evoked fields (ssVEFs). Linear regression models were conducted to explore clinical correlates of brain activity. RESULTS: Although no interaction group × picture category × brain region was found, a significant interaction group × brain region appeared for orbito-frontal cortex (OFC). BPD patients showed significantly reduced magnetocortical activity in left OFC across all picture categories (F = 26.4; p<.05; F = 31.4). Left OFC activity was inversely correlated with depression score in the BDI (r: -0.48, p < 0.05), with score in the Cornell Dysthymia rating scale (r: -0.52, p < 0.05) and with the number of criteria met for depressive personality disorder (r: -0.44, p < 0.05). Left orbitofrontal activity was also inversely correlated with the global score in the GAF (r-0.63, p < 0.01). No correlations were found between OFC activity and impulsivity or global severity of BPD symptoms. CONCLUSIONS: Abnormal functioning at orbitofrontal areas in BPD could be related to the presence of affective symptomatology and is associated with greater functional deterioration of patients.

A Joint Experimental and Theoretical Study of the Interaction between Aluminum and Electroluminescent Polymers: Cyano Derivatives of Poly(p-phenylene vinylene).

The early stages of metal/polymer interface formation between aluminum and poly(2,5,2',5'-tetrahexyloxy-8,7'-dicyanodi-p-phenylenevinylene) or their ring-substituted derivatives have been studied theoretically by using quantum-chemical calculations as well as experimentally by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. This class of conjugated polymer is of interest in the development of organic light-emitting diodes. The theoretical and experimental results indicate that aluminum preferentially reacts with the polymer by forming covalent bonds with the nitrogen and carbon atoms of the cyano groups. When the side chains of the phenylene rings include carbonyl groups, however, the theoretical results indicate that the carbonyl moiety is another preferred site of interaction.