Post-training inactivation of the anterior thalamic nuclei impairs spatial performance on the radial arm maze

The limbic thalamus, specifically the anterior thalamic nuclei (ATN), contains brain signals including that of head direction cells, which fire as a function of an animal\u27s directional orientation in an environment. Recent work has suggested that this directional orientation information stemming from the ATN contributes to the generation of hippocampal and parahippocampal spatial representations, and may contribute to the establishment of unique spatial representations in radially oriented tasks such as the radial arm maze. While previous studies have shown that ATN lesions can impair spatial working memory performance in the radial maze, little work has been done to investigate spatial reference memory in a discrimination task variant. Further, while previous studies have shown that ATN lesions can impair performance in the radial maze, these studies produced the ATN lesions prior to training. It is therefore unclear whether the ATN lesions disrupted acquisition or retention of radial maze performance. Here, we tested the role of ATN signaling in a previously learned spatial discrimination task on a radial arm maze. Rats were first trained to asymptotic levels in a task in which two maze arms were consistently baited across training. After 24 h, animals received muscimol inactivation of the ATN before a 4 trial probe test. We report impairments in post-inactivation trials, suggesting that signals from the ATN modulate the use of a previously acquired spatial discrimination in the radial-arm maze. The results are discussed in relation to the thalamo-cortical limbic circuits involved in spatial information processing, with an emphasis on the head direction signal. © 2017 Harvey, Thompson, Sanchez, Yoder and Clark

Bodily tides near spin-orbit resonances

Spin-orbit coupling can be described in two approaches. The method known as "the MacDonald torque" is often combined with an assumption that the quality factor Q is frequency-independent. This makes the method inconsistent, because the MacDonald theory tacitly fixes the rheology by making Q scale as the inverse tidal frequency. Spin-orbit coupling can be treated also in an approach called "the Darwin torque". While this theory is general enough to accommodate an arbitrary frequency-dependence of Q, this advantage has not yet been exploited in the literature, where Q is assumed constant or is set to scale as inverse tidal frequency, the latter assertion making the Darwin torque equivalent to a corrected version of the MacDonald torque. However neither a constant nor an inverse-frequency Q reflect the properties of realistic mantles and crusts, because the actual frequency-dependence is more complex. Hence the necessity to enrich the theory of spin-orbit interaction with the right frequency-dependence. We accomplish this programme for the Darwin-torque-based model near resonances. We derive the frequency-dependence of the tidal torque from the first principles, i.e., from the expression for the mantle's compliance in the time domain. We also explain that the tidal torque includes not only the secular part, but also an oscillating part. We demonstrate that the lmpq term of the Darwin-Kaula expansion for the tidal torque smoothly goes through zero, when the secondary traverses the lmpq resonance (e.g., the principal tidal torque smoothly goes through nil as the secondary crosses the synchronous orbit). We also offer a possible explanation for the unexpected frequency-dependence of the tidal dissipation rate in the Moon, discovered by LLR

The CO₂ dependence of photosynthesis, plant growth responses to elevated CO₂ concentrations and their interaction with soil nutrient status, II. Temperate and boreal forest productivity and the combined effects of increasing CO₂ concentrations and increased nitrogen deposition at a global scale

1. Appropriate rates of carbon acquisition by temperate and boreal forests are re-evaluatted, Based on continental-scale forestry data it is suggested that the productivity of temperate and boreal forests has been overestimated previously. 2, Using these values, a model of the integrated response of ecosystems to carbon dioxide concentration and soil nitrogen availability is presented. The model does not assume constant C/N ratios in plant or soil and considers effects of increases in atmospheric CO2 concentrations and nitrogen deposition separately or together. 3, For temperate-zone forests a co-occurrence of a CO2 increase and nitrogen deposition doubles the increase in net primary productivity and carbon sequestration that would be the case for nitrogen deposition occurring on its own. Considered separately, the effect of the atmospheric CO2 increase is less than even moderate rates of anthropogenic N deposition for temperate or boreal forests. By contrast, for tropical forests, the atmospheric CO2 increase is sufficient to induce large rates of carbon accumulation in plants and soil. 4, Application of the model at the global scale suggests large localized sinks for CO2 in either tropical rain forests or in forested or grassland areas of Europe and North America where appreciable N deposition occurs. Overall, the model suggests a terrestrial sink owing to CO2 fertilization and N deposition of about 0.2 Pmol C per year. About half of this is in the mid-latitudes of the northern hemisphere and about half in the tropics. [References: 107