Statistics of trajectories in two-state master equations

We derive a simple expression for the probability of trajectories of a master equation. The expression is particularly useful when the number of states is small and permits the calculation of observables that can be defined as functionals of whole trajectories. We illustrate the method with a two-state master equation, for which we calculate the distribution of the time spent in one state and the distribution of the number of transitions, each in a given time interval. These two expressions are obtained analytically in terms of modified Bessel functions.Comment: 4 pages, 3 figure

Quantum simulation of multiple-exciton generation in a nanocrystal by a single photon

We have shown theoretically that efficient multiple exciton generation (MEG) by a single photon can be observed in small nanocrystals (NCs). Our quantum simulations that include hundreds of thousands of exciton and multi-exciton states demonstrate that the complex time-dependent dynamics of these states in a closed electronic system yields a saturated MEG effect on a picosecond timescale. Including phonon relaxation confirms that efficient MEG requires the exciton--biexciton coupling time to be faster than exciton relaxation time

Heat shock factor 1 regulates lifespan as distinct from disease onset in prion disease

Prion diseases are fatal, transmissible, neurodegenerative diseases caused by the misfolding of the prion protein (PrP). At present, the molecular pathways underlying prion-mediated neurotoxicity are largely unknown. We hypothesized that the transcriptional regulator of the stress response, heat shock factor 1 (HSF1), would play an important role in prion disease. Uninoculated HSF1 knockout (KO) mice used in our study do not show signs of neurodegeneration as assessed by survival, motor performance, or histopathology. When inoculated with Rocky Mountain Laboratory (RML) prions HSF1 KO mice had a dramatically shortened lifespan, succumbing to disease ≈20% faster than controls. Surprisingly, both the onset of home-cage behavioral symptoms and pathological alterations occurred at a similar time in HSF1 KO and control mice. The accumulation of proteinase K (PK)-resistant PrP also occurred with similar kinetics and prion infectivity accrued at an equal or slower rate. Thus, HSF1 provides an important protective function that is specifically manifest after the onset of behavioral symptoms of prion disease

Neural circuits involved in imitation and perspective-taking

Is it important to adopt the perspective of the model when learning a new skill? Is the “mirror system” equally involved when the teacher is facing or side-by-side with students? In this functional MRI study, we measured the cerebral hemodynamic changes in participants who watched video-clips depicting simple hand or foot actions. The participants either watched passively or imitated these actions. Half the video-clips depicted actions filmed from the perspective of the participant (1st-person perspective) and half from a frontal view as if watching someone else (3rd-person perspective). Behavioral results showed that latency to imitate was significantly shorter for the 1st-person perspective than the 3rd-person perspective. Functional imaging results demonstrate that the observation of intransitive actions engaged primary visual and extrastriate visual areas, but not the premotor cortex. Imitation vs. observation of actions yielded enhanced signal in the contralateral somatosensory and motor cortices, cerebellum, left inferior parietal lobule and superior parietal cortex, and left ventral premotor cortex. Activity in the lateral occipital cortex around the extrastriate body area was significantly enhanced during imitation, as compared to observation of actions confirming that this region involvement reaches beyond the perception of body parts. Moreover, comparisons of the two visual perspectives showed more activity in the left sensory–motor cortex for 1st-person, even during observation alone, and in the lingual gyrus for 3rd-person perspective. These findings suggest that the 1st-person perspective is more tightly coupled to the sensory-motor system than the 3rd-person perspective, which requires additional visuospatial transformation

Body size as a driver of scavenging in theropod dinosaurs

This work was funded by the Earth and Natural Sciences Doctoral Studies Programme and the Higher Education Authority through the Programme for Research at Third Level Institutions, Cycle 5 (PRTLI‐5), and cofunded by the European Regional Development Fund (K.H.) and Trinity College Dublin and the Irish Research Council (A.K.).Theropod dinosaurs dominated Earth’s terrestrial ecosystem as a diverse group of predators for more than 160 million years, yet little is known about their foraging ecology. Maintaining a balanced energy budget presented a major challenge for therapods, which ranged from the chicken-sized Microraptor up to the whale-sized Giganotosaurus, in the face of intense competition and the demands of ontogenetic growth. Facultative scavenging, a behavior present in almost all modern predators, may have been important in supplementing energetically expensive lifestyles. By using agentbased models based on the allometric relationship between size and foraging behaviors, we show that theropods between 27 and 1,044 kg would have gained a significant energetic advantage over individuals at both the small and large extremes of theropod body mass through their scavenging efficiency. These results were robust to rate of competition, primary productivity, and detection distance. Our models demonstrate the potential importance of facultative scavenging in theropods and the role of body size in defining its prevalence in Mesozoic terrestrial systems.Publisher PDFPeer reviewe

Editorial: Mental practice: Clinical and experimental research in imagery and action observation

First paragraph: This editorial accompanies 18 articles as part of aFrontiersresearch topic. The aim of this research topic was to clarify the underlying mechanisms involved in mental practice of action, bringing together evidence from a range of disciplines including cognitive neuroscience, experimental neuropsychology, sport and movement science, clinical neuropsychology and clinical neurology. The need to clarify the underlying mechanisms of mental practice is a pressing one. Mental practice of action has been explored in sport psychology for several decades, with the aim to use mental practice to improve sport performance. However, following the discovery of the mirror neuron system (see for example,Rizzolatti and Craighero, 2004), the perspective of mental practice has changed to a rationale based on neuroscience and to research focussed on understanding the neural processes of mental practice. Evidence that the brain simulates action has resulted in a common understanding of “functional equivalence” (Jeannerod, 1994): the idea that thementalrepresentation of an action or percept in the person's mind is the neural “equivalent” to thephysicalaction oractualpercept. This ability to mentally represent action using the motor system allows for action simulation, providing conscious mental rehearsal of movement (imagery), but also allows for a common percept when observing the movements of others. Finally, in recent years, the disciplines of clinical neuropsychology and neurology have begun to use mental rehearsal of action, ormental practice, to produce improvements normally attributed to practicing actual movements