Demonstration of Single-Barium-Ion Sensitivity for Neutrinoless Double-Beta Decay Using Single-Molecule Fluorescence Imaging.

A new method to tag the barium daughter in the double-beta decay of ^{136}Xe is reported. Using the technique of single molecule fluorescent imaging (SMFI), individual barium dication (Ba^{++}) resolution at a transparent scanning surface is demonstrated. A single-step photobleach confirms the single ion interpretation. Individual ions are localized with superresolution (∼2 nm), and detected with a statistical significance of 12.9σ over backgrounds. This lays the foundation for a new and potentially background-free neutrinoless double-beta decay technology, based on SMFI coupled to high pressure xenon gas time projection chambers.

Development and adult phase plasticity of syllable repetitions in the birdsong of captive zebra finches (Taeniopygia guttata).

Oscines learn their birdsongs from tutors. The authors found that a small fraction (approximately 7%) of captive male zebra finches (Taeniopygia guttata) produce variant acoustic birdsong profiles consisting of repetitions of single song syllables at high frequencies. Juvenile offspring of nonrepeaters can selectively learn the syntactic rule or habit of repeating syllables from repeaters. Adult tutored syllable repeaters, unlike spontaneous repeaters, undergo a form of song plasticity involving progressive reduction of the mean number and variance of repeated syllables as a function of long-term exposure to nonrepeater songs without altering the number or sequence of syllables within motifs. These findings suggest that aspects of song syntax or temporal frame can be acquired independently of song syllable or spectral content, and plasticity involving restorative alteration of acquired variant temporal frames can occur after the closure of the critical period for song learning.

Reduction of female-directed song motifs induced by repeated singing in laboratory-bred zebra finches.

Songbirds such as zebra finches show a remarkable degree of neural plasticity associated with the motor act of singing. Here we show that in adult male zebra finches repeated female-directed singing episodes are associated with a change in subsequent singing behavior involving a progressive long-lasting decline in the number of song motifs sung. This reduction in song motif production cannot be completely explained by the circadian rhythm, declining motivation or neuromuscular exhaustion. Paired song induction sessions reveal that the time course of motif reduction during repeated singing can be best explained by the cumulative effect of reduction produced by each singing episode. These results suggest that song production in zebra finches is prone to a form of rapid behavioral adaptation.