Dopaminergic error signals retune to social feedback during courtship.

Hunger, thirst, loneliness and ambition determine the reward value of food, water, social interaction and performance outcome. Dopamine neurons respond to rewards meeting these diverse needs, but it remains unclear how behaviour and dopamine signals change as priorities change with new opportunities in the environment. One possibility is that dopamine signals for distinct drives are routed to distinct dopamine pathways.

Dopamine neurons evaluate natural fluctuations in performance quality.

Many motor skills are learned by comparing ongoing behavior to internal performance benchmarks. Dopamine neurons encode performance error in behavioral paradigms where error is externally induced, but it remains unknown whether dopamine also signals the quality of natural performance fluctuations. Here, we record dopamine neurons in singing birds and examine how spontaneous dopamine spiking activity correlates with natural fluctuations in ongoing song.

Movement signaling in ventral pallidum and dopaminergic midbrain is gated by behavioral state in singing birds.

Movement-related neuronal discharge in ventral tegmental area (VTA) and ventral pallidum (VP) is inconsistently observed across studies. One possibility is that some neurons are movement related and others are not. Another possibility is that the precise behavioral conditions matter-that a single neuron can be movement related under certain behavioral states but not others.

Dopamine neurons encode performance error in singing birds.

Many behaviors are learned through trial and error by matching performance to internal goals. Yet neural mechanisms of performance evaluation remain poorly understood. We recorded basal ganglia-projecting dopamine neurons in singing zebra finches as we controlled perceived song quality with distorted auditory feedback.

A variability-generating circuit goes awry in a songbird model of the FOXP2 speech disorder.

FOXP2 mutations cause a monogenic speech disorder in humans. In this issue of Neuron, Murugan et al. (2013) show that knockdown of FoxP2 in the songbird basal ganglia causes abnormal vocal variability and excess bursting in a frontal cortical nucleus.

Irreversible pressure-induced transformation of boron nitride nanotubes.

We have used Raman spectroscopy to study the behavior of multi-walled boron nitride nanotubes and hexagonal boron nitride crystals under high pressure. While boron nitride nanotubes show an irreversible transformation at about 12 GPa, hexagonal boron nitride exhibits a reversible phase transition at 13 GPa. We also present molecular dynamics simulations which suggest that the irreversibility of the pressure-induced transformation in boron nitride nanotubes is due to the polar nature of the bonds between boron and nitrogen.

Double-walled carbon nanotubes under hydrostatic pressure: Raman experiments and simulations.

We have used Raman spectroscopy to study the behavior of double-walled carbon nanotubes (DWNT) under hydrostatic pressure. We find that the rate of change of the tangential mode frequency with pressure is higher for the sample with traces of polymer compared to the pristine sample. We have performed classical molecular dynamics simulations to study the collapse of single (SWNT) and double-walled carbon nanotube bundles under hydrostatic pressure.

Faster development does not lead to correlated evolution of greater pre-adult competitive ability in Drosophila melanogaster.

In comparisons across Drosophila species, faster pre-adult development is phenotypically correlated with increased pre-adult competitive ability, suggesting that these two traits may also be evolutionary correlates of one another. However, correlations between traits within- and among- species can differ, and in most cases it is the within-species genetic correlations that are likely to act as constraints on adaptive evolution. Moreover, laboratory studies on Drosophila melanogaster have shown that the suite of traits that evolves in populations subjected to selection for faster development is the opposite of the traits that evolve in populations selected for increased pre-adult competitive ability.