Gamma band modulations in neural activity have been proposed to mediate attentional processes. To support a causal link between gamma activity and attentional selection, we attempt to evoke gamma oscillations by a 50-Hz subliminal flicker. We find that a subliminal 50-Hz flicker at a target location, before target presentation, speeds up and enhances target detection and discrimination. This effect is specific to the middle of the gamma range because it is not evident at <35-Hz flicker. It requires 300 ms to build up, dissipates within 250 ms of flicker offset, and shows a tendency to invert after 500 ms. The results are discussed in relation to a role for gamma band neural synchrony in the allocation of visual attention.visual attention ͉ neural synchrony ͉ gamma ͉ psychophysics ͉ subliminal T he nature of the neural mechanisms underlying visual attention-the ability of humans and animals to select a limited number of stimuli from the multitude simultaneously present in the visual field for prioritized processing-remains a fundamental problem in visual neuroscience (1). A complete theory of visual attention must explain how the relative salience of selected stimuli is enhanced in neural terms, even though they are often not singled out by increased firing rates (2, 3). One recently proposed solution is the ''Attention-Gamma'' hypothesis, according to which synchronized gamma band (40-70 Hz) modulations in neural activity mediate attentional processes (4-10). This hypothesis is supported by a correlation, across trials, between the speed of behavioral responses in a visual detection task and the power in the gamma frequency range of V4 neurons (10-12). In these studies, Fries, Womelsdorf, and colleagues demonstrated that top-down visual attention is associated with internal gamma band synchrony in task-specific neural populations, which could be generated by top-down attentional modulations (13, 14). Thus, it is possible that selected neural representations are given a gamma band oscillatory tag by a top-down attention mechanism (15). If this is the case, it may be possible to trigger the effects of selective attention (enhanced selection and perception) by externally evoking gamma band oscillations of the relevant neural representation, thus mimicking the attentional tag.To test this hypothesis, we examined whether external stimulus flicker at a specific location, which is expected to evoke phaselocked neural activity at the same frequency, results in attentional orientation to that location in the absence of conscious detection of the flicker; if the flicker were detectable, it could lead to an orienting of attention toward its location as a result of exogenous or endogenous processes that are not specific to the temporal modulation. To test whether subliminally evoked neural synchronization has an attentional effect, we built on recent studies demonstrating that visual flicker in the midgamma band range (40-70 Hz) entrains periodic neural responses at the same frequency in the visual cortex [refs. 16 and 17; ...

The body schema, a constantly updated representation of the body and its parts, has been suggested to emerge from body part-specific representations which integrate tactile, visual, and proprioceptive information about the identity and posture of the body. Studies using different approaches have provided evidence for a distinct representation of the visual space approximately 30 cm around the upper body, and predominantly the hands, termed the peripersonal space. In humans, peripersonal space representations have often been investigated with a visual-tactile crossmodal congruency task. We used this task to test if a representation of peripersonal space exists also around the feet, and to explore possible interactions of peripersonal space representations of different body parts. In Experiment 1, tactile stimuli to the hands and feet were judged according to their elevation while visual distractors presented near the same limbs had to be ignored. Crossmodal congruency effects did not differ between the two types of limbs, suggesting a representation of peripersonal space also around the feet. In Experiment 2, tactile stimuli were presented to the hands, and visual distractors were flashed either near the participant's foot, near a fake foot, or in distant space. Crossmodal congruency effects were larger in the real foot condition than in the two other conditions, indicating interactions between the peripersonal space representations of foot and hand. Furthermore, results of all three conditions showed that vision of the stimulated body part, compared to only proprioceptive input about its location, strongly influences crossmodal interactions for tactile perception, affirming the central role of vision in the construction of the body schema.

SummaryPorin (PorB), the major outer membrane protein of Neisseria gonorrhoeae, has been implicated in pathogenesis previously. However, the fact that porin deletion mutants are not viable has complicated investigations. Here, we describe a method of manipulating the porin gene site-specifically. N. gonorrhoeae MS11, which harbours the porB 1B (P.1B) porin allele, was used to generate mutants carrying deletions in the surface loops 1 and 5. An 11-amino-acid deletion in loop 1 impaired Opa 50 -dependent invasion into human Chang epithelial cells, whereas loop 5 deletion exhibited no apparent phenotype. In a second approach, the complete gonococcal porB 1B was replaced by the porB Nla gene of Neisseria lactamica. Such mutants were unable to induce efficient uptake by epithelial cells but induced an enhanced respiratory response in HL60 phagocytic cells. The increased respiratory burst was accompanied by an enhanced phagocytic uptake of the mutant compared with the wild-type strain. Our data extend previous evidence for multiple central functions of PorB in the infection process.

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Visual binding is the process by which the brain groups the elements belonging to one object, whilst segregating them from other scene elements. A computationally parsimonious mechanism of visual binding is the binding-by-synchrony (BBS) hypothesis. According to this hypothesis, detectors that respond to elements of a single object fire in synchrony, while detectors that respond to elements of different objects do not. Current psychophysical and physiological evidence are inconclusive about the role of BBS in the visual integration process. Here we provide psychophysical and computational evidence suggesting that the visual system implements a mechanism that synchronizes response onsets to object parts and attenuates or cancels their latency differences. In three experiments, observers had to judge the synchrony of two flickering Gabor patches embedded in a static Gabor contour, passing through fixation. We found that a smooth contour, as compared to a jagged one, impedes judgments of temporal synchrony between the targets, whilst facilitating non-temporal judgments of contrast on the same targets. We show that the results are consistent with a simple computational model that implements synchronization of responses via lateral interactions, enabling the visual system to pick up objects by synchrony among a temporally diverse background.