Good vibrations: oscillatory phase shapes perception.

In the current study, we provide compelling evidence to answer the long-standing question whether perception is continuous or periodic. Spontaneous brain oscillations are assumed to be the underlying mechanism of periodic perception. Depending on the phase angle of the oscillations, an identical stimulus results in different perceptual outcomes. Past results, however, can only account for a correlation of perception with the phase of the ongoing brain oscillations. Therefore, it is desirable to demonstrate a causal relation between phase and perception. One way to address this question is to entrain spontaneous brain oscillations by applying an external oscillation and then demonstrate behavioral consequences of this oscillation. We conducted an auditory detection experiment with humans, recorded the electroencephalogram (EEG) concurrently and simultaneously applied oscillating transcranial direct current stimulation at 10Hz (α-tDCS). Our approach revealed that detection thresholds were dependent on the phase of the oscillation that was entrained by α-tDCS. This behavioral effect was accompanied by an electrophysiological effect: α-power was enhanced after α-tDCS as compared to a pre-stimulation period. By showing a causal relation between phase and perception, our results extend findings of previous studies that were only able to demonstrate a correlation. We found that manipulation of the phase resulted in different detection thresholds, which supports the notion that perception can be periodically modulated by oscillatory processes. This demonstrates that tDCS can serve as a tool in neuroscience to extend the knowledge of the functional significance of brain oscillations.

[Carticaine and mepivacaine. a double blindstudy on longterm and diffusion action during blockade of the brachial plexus (author's transl)]. / Carticain und Mepivacain Doppelblindstudie über Latenzzeit und Diffusionsverhalten bei der Blockade des Plexus brachialis.

In a double blind study, using supraclavicular plexus blockade as a model, the latency and diffusion of carticaine in comparison with mepivacain was investigated. Up to 16 min after first eliciting paraesthesiae and injection somewhat more plexus blocks were complete with carticain than with mepivacaine. This difference was statistically valid only for motor block and not for sensory block. However, the relative proportion of complete motor and sensory block increased with mepivacain after 16 min and surpassed the results for carticaine. This difference is statistically significant for sensory block and for sensory and motor block combined. It is also valid for the results up to 30 min. The failure rate was significantly higher for carticaine than for mepivacaine. From these results the course and the failures are attributed to a poorer diffusion of carticaine.