Latent Dynamical Variables Produce Signatures of Spatiotemporal Criticality in Large Biological Systems.

Understanding the activity of large populations of neurons is difficult due to the combinatorial complexity of possible cell-cell interactions. To reduce the complexity, coarse graining had been previously applied to experimental neural recordings, which showed over two decades of apparent scaling in free energy, activity variance, eigenvalue spectra, and correlation time, hinting that the mouse hippocampus operates in a critical regime. We model such data by simulating conditionally independent binary neurons coupled to a small number of long-timescale stochastic fields and then replicating the coarse-graining procedure and analysis. This reproduces the experimentally observed scalings, suggesting that they do not require fine-tuning of internal parameters, but will arise in any system, biological or not, where activity variables are coupled to latent dynamic stimuli. Parameter sweeps for our model suggest that emergence of scaling requires most of the cells in a population to couple to the latent stimuli, predicting that even the celebrated place cells must also respond to nonplace stimuli.

Do looks matter? The role of the Electronic Residency Application Service photograph in dermatology residency selection.

BACKGROUND: There is a lack of research on the impact of the Electronic Residency Application Service (ERAS) photograph on the residency selection process. OBJECTIVE: We sought to elucidate the role of the ERAS photograph in the dermatology residency selection outcome and to determine if photographs submitted by matched applicants differ from those of unmatched applicants. METHODS: We analyzed ERAS photographs submitted by dermatology residency applicants based on photograph characteristics related to composition, attire, facial expression, hairstyle, and accessories. RESULTS: Candidates who smiled, wore glasses, and wore jackets in their photographs were more likely to match. There was no difference in the rate of matching among applicants depending on whether their photograph was of professional quality or whether they wore formal attire in their pictures. Gender specific characteristics were not found to be influential in the match outcome for male applicants. Among female applicants, having hair to the shoulders or longer was associated with a positive match outcome. CONCLUSION: Certain characteristics of the ERAS photographs were found to be associated with a more favorable match outcome. Further biases inferred from these photographs might be present in the dermatology selection process. We suggest blinding the selection committees to ERAS application photographs prior to granting residency interviews.

Spectral holographic trapping: Creating dynamic force landscapes with polyphonic waves.

Acoustic trapping uses forces exerted by sound waves to transport small objects along specified trajectories in three dimensions. The structure of the time-averaged acoustic force landscape acting on an object is determined by the amplitude and phase profiles of the sound's pressure wave. These profiles typically are sculpted by deliberately selecting the amplitude and relative phase of the sound projected by each transducer in large arrays of transducers, all operating at the same carrier frequency. This approach leverages a powerful analogy with holographic optical trapping at the cost of considerable technical complexity. Acoustic force fields also can be shaped by the spectral content of the component sound waves in a manner that is not feasible with light. The same theoretical framework that predicts the time-averaged structure of monotone acoustic force landscapes can be applied to spectrally rich sound fields in the quasistatic approximation, creating opportunities for dexterous control using comparatively simple hardware. We demonstrate this approach to spectral holographic acoustic trapping by projecting acoustic conveyor beams that move millimeter-scale objects along prescribed paths. Spectral control of reflections provides yet another opportunity for controlling the structure and dynamics of an acoustic force landscape. We use this approach to realize two variations on the theme of a wave-driven oscillator, a deceptively simple dynamical system with surprisingly complex phenomenology.

Neural criticality from effective latent variables.

Observations of power laws in neural activity data have raised the intriguing notion that brains may operate in a critical state. One example of this critical state is 'avalanche criticality', which has been observed in various systems, including cultured neurons, zebrafish, rodent cortex, and human EEG. More recently, power laws were also observed in neural populations in the mouse under an activity coarse-graining procedure, and they were explained as a consequence of the neural activity being coupled to multiple latent dynamical variables. An intriguing possibility is that avalanche criticality emerges due to a similar mechanism. Here, we determine the conditions under which latent dynamical variables give rise to avalanche criticality. We find that populations coupled to multiple latent variables produce critical behavior across a broader parameter range than those coupled to a single, quasi-static latent variable, but in both cases, avalanche criticality is observed without fine-tuning of model parameters. We identify two regimes of avalanches, both critical but differing in the amount of information carried about the latent variable. Our results suggest that avalanche criticality arises in neural systems in which activity is effectively modeled as a population driven by a few dynamical variables and these variables can be inferred from the population activity.