Regulation of fast-spiking basket cell synapses by the chloride channel ClC-2.

Parvalbumin-expressing, fast-spiking basket cells are important for the generation of synchronous, rhythmic population activities in the hippocampus. We found that GABAA receptor-mediated synaptic inputs from murine parvalbumin-expressing basket cells were selectively modulated by the membrane voltage- and intracellular chloride-dependent chloride channel ClC-2. Our data reveal a previously unknown cell type-specific regulation of intracellular chloride homeostasis in the perisomatic region of hippocampal pyramidal neurons

Learning a Bayesian prior in interval timing

Behavioral studies on perceptual learning (PL) often attributed an improvement in task performance to an enhancement in sensory processing of stimuli. However, the framework of Bayesian inference suggests that perceptual improvements can arise from learning-induced changes either in a likelihood function or in a prior expectation for sensory input. We developed and adapted Bayesian observer models to long-term changes in interval timing (IT) performance by human subjects to assess relative contributions of the prior and likelihood to PL of IT.

While subjects were viewing a small bar that drifted for a while and disappeared, we estimated subjective time intervals ([DELTA]Ts) from subjects’ natural reactions to the reappearance of the invisible bar at a designated location, with the speed and distance of invisible motion varied trial to trial. Ten subjects performed this task over 10 daily sessions for [DELTA]Ts ranging from 0.5 to 6.5 sec. 

In terms of timing accuracy, the trend that short and long [DELTA]Ts were overestimated and underestimated, respectively, was evident in all subjects and became stronger over sessions. In contrast, timing precision gradually improved over session for the entire set of sampled [DELTA]Ts. These seemingly contradictory dynamics of PL in accuracy and precision were captured simultaneously by Bayesian models, in which subjective timing is determined jointly by the prior and likelihood function for IT. The best among several nested models was a simple model in which only a single Gaussian function and a single coefficient of variance were set free to describe the prior and the likelihood functions, respectively. Interestingly, it was the spread of the prior, not the likelihood, that changed steadily in the model fit to the across-session data, suggesting that the improvements in timing precision observed in our and previous studies arose as the prior became sharpened through massive training.
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Stimulus Fractionation by Interocular Suppression

Can human observers distinguish physical removal of a visible stimulus from phenomenal suppression of that stimulus during binocular rivalry? As so often happens, simple questions produce complex answers, and that is the case in the study reported here. Using continuous flash suppression to produce binocular rivalry, we were able to identify stimulus conditions where most – but not all – people utterly fail to distinguish physical from phenomenal stimulus removal, although we can be certain that those two equivalent perceptual states are accompanied by distinct neural events. More interestingly, we find subtle variants of the task where distinguishing the two states is trivially easy, even for people who utterly fail under the original conditions. We found that stimulus features are differentially vulnerable to suppression. Observers are able to be aware of existence/removal of some stimulus attributes (flicker) but not others (orientation), implying that interocular suppression breaks down the unitary awareness of integrated features belonging to a visual object. These findings raise questions about the unitary nature of awareness and, also, place qualifications on the utility of binocular rivalry as a tool for studying the neural concomitants of conscious visual awareness

Scanning optical homodyne detection of high-frequency picoscale resonances in cantilever and tuning fork sensors

Higher harmonic modes in nanoscale silicon cantilevers and microscale quartz tuning forks are detected and characterized using a custom scanning optical homodyne interferometer. Capable of both mass and force sensing, these resonators exhibit high-frequency harmonic motion content with picometer-scale amplitudes detected in a 2.5 MHz bandwidth, driven by ambient thermal radiation. Quartz tuning forks additionally display both in-plane and out-of-plane harmonics. The first six electronically detected resonances are matched to optically detected and mapped fork eigenmodes. Mass sensing experiments utilizing higher tuning fork modes indicate >6x sensitivity enhancement over fundamental mode operation.Comment: 3 pages, 3 figures, submitted to Applied Physics Letter