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"Compasses"
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Population dynamics of head-direction neurons during drift and reorientation
The head direction (HD) system functions as the brain’s internal compass
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, classically formalized as a one-dimensional ring attractor network
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. In contrast to a globally consistent magnetic compass, the HD system does not have a universal reference frame. Instead, it anchors to local cues, maintaining a stable offset when cues rotate
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and drifting in the absence of referents
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,
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. However, questions about the mechanisms that underlie anchoring and drift remain unresolved and are best addressed at the population level. For example, the extent to which the one-dimensional description of population activity holds under conditions of reorientation and drift is unclear. Here we performed population recordings of thalamic HD cells using calcium imaging during controlled rotations of a visual landmark. Across experiments, population activity varied along a second dimension, which we refer to as network gain, especially under circumstances of cue conflict and ambiguity. Activity along this dimension predicted realignment and drift dynamics, including the speed of network realignment. In the dark, network gain maintained a ‘memory trace’ of the previously displayed landmark. Further experiments demonstrated that the HD network returned to its baseline orientation after brief, but not longer, exposures to a rotated cue. This experience dependence suggests that memory of previous associations between HD neurons and allocentric cues is maintained and influences the internal HD representation. Building on these results, we show that continuous rotation of a visual landmark induced rotation of the HD representation that persisted in darkness, demonstrating experience-dependent recalibration of the HD system. Finally, we propose a computational model to formalize how the neural compass flexibly adapts to changing environmental cues to maintain a reliable representation of HD. These results challenge classical one-dimensional interpretations of the HD system and provide insights into the interactions between this system and the cues to which it anchors.
Mice maintain the memory of previous associations between head direction neurons and allocentric cues and this influences the internal head direction representation.
Journal Article
The geomancer's compass
\"Set in the year 2021, this novel explores the tension between a young woman's future building infrastructure for Augmented Reality, and the commitment she makes to her dying grandmother to honor ancient Chinese magic\"--Provided by publisher.
Book
Chiral-induced spin selectivity in the formation and recombination of radical pairs: cryptochrome magnetoreception and EPR detection
That the rates and yields of reactions of organic radicals can be spin dependent is well known in the context of the radical pair mechanism (RPM). Less well known, but still well established, is the chiral-induced spin selectivity (CISS) effect in which chiral molecules act as spin filters that preferentially transmit electrons with spins polarized parallel or antiparallel to their direction of motion. Starting from the assumption that CISS can arise in electron transfer reactions of radical pairs, we propose a simple way to include CISS in conventional models of radical pair spin dynamics. We show that CISS can (a) increase the sensitivity of radical pairs to the direction of a weak external magnetic field, (b) change the dependence of the magnetic field effect on the reaction rate constants, and (c) destroy the field-inversion symmetry characteristic of the RPM. We argue that CISS polarization effects could be observable by EPR (electron paramagnetic resonance) of oriented samples either as differences in continuous wave, time-resolved spectra recorded with the spectrometer field parallel or perpendicular to the CISS quantization axis or as signals in the in-phase channel of an out-of-phase ESEEM (electron spin echo envelope modulation) experiment. Finally we assess whether CISS might be relevant to the hypothesis that the magnetic compass of migratory songbirds relies on photochemically-formed radical pairs in cryptochrome flavoproteins. Although CISS effects offer the possibility of evolving a more sensitive or precise compass, the associated lack of field-inversion symmetry has not hitherto been observed in behavioural experiments. In addition, it may no longer be safe to assume that the observation of a polar magnetic compass response in an animal can be used as evidence against a radical pair sensory mechanism.
Journal Article
Monarch butterflies (Danaus plexippus) only use magnetic cues for migratory directionality with orientation re-calibrated by coldness
Each fall, Eastern North American monarch butterflies ( Danaus plexippus ) leave their northern range and migrate to their overwintering sites high atop mountains in central Mexico. Although monarchs primarily rely on the use of a bidirectional time-compensated sun compass to maintain southwards directionality en route to Mexico, on overcast sky days when directional daylight cues are unavailable, monarchs can use an inclination-based magnetic compass to maintain correct directionality. As compass cues can only be used to determine direction, monarchs must use other mechanisms for recognizing, locating, and ultimately stopping at their overwintering sites. Although previous work found no evidence of monarchs using a fine-scale magnetic map for locating their specific overwintering sites, monarchs might still use magnetic cues in a general sense, such as when recognizing that they have overshot their destination or have gone off course. Here, using righting response orientation trials, we show that fall monarchs maintain equatorward (southward) orientation even when tested under artificially generated magnetic field conditions consistent with either their overwintering sites or magnetic conditions geographically south of these sites. We also found that fall migrants exposed to overwintering-like coldness reverse their orientation poleward (northward). This result indicates that the monarch’s magnetic compass is also recalibrated by the cold temperature microenvironment at the overwintering sites, as has been shown previously with its time-compensated sun compass. Our results indicate that migratory monarchs must use other cues for locating and stopping at their migratory destination. Our discovery that coldness recalibrates multiple compass mechanisms in a long-distance migratory species underscores the threat of climate change and corresponding increasing temperatures on animal migration.
Journal Article
Orienting paleomagnetic drill cores using a portable GPS compass
A portable Global Positioning System (GPS) compass was devised for orienting paleomagnetic drill cores and field test measurements were conducted. Orientation of drill cores has been done by magnetic compasses, sun compasses, and backsighting using landmarks. We modified a lightweight marine GPS compass to be mounted on an orientation device and directly measure azimuths, and compared them to measurements made with a magnetic compass, sun compass, and backsighting. Tests on our campus for a site with open sky above showed a root-mean-squared (rms) error of 0.39∘, which is less than what is noted on the specifications of the GPS compass, and a difference of -0.1∘±1.1∘ (average ± rms) between the GPS and sun azimuths for 11 direction measurements. However, the site between buildings showed an average deviation of 11.4∘ from the sun azimuth due to multipath effects. When tested on drill core sampling of historical lavas in a volcanic island, the GPS azimuths were deviated only by 0.4∘±2.3∘ from the sun azimuths at a flat coastal site with open sky above, indicating that the GPS azimuths are as accurate as the sun azimuths. On the other hand, the GPS compass could not provide azimuths at vertical outcrops in forests due to the small number of satellites captured and multipath effects. If other Global Navigation Satellite Systems (GNSS) satellites are captured and false signals caused by multipath are eliminated, portable GNSS compasses, which operate regardless of rock type, weather, or geographic situation, would replace other methods of orienting drill cores.
Journal Article
Compass adjustment by GPS (or any other GNSS receiver) and a single visual reference
This paper proposes a proper compass adjustment method using only a GPS (or any other GNSS receiver) and a single visual reference to enhance the efficiency of compass adjustment. During compass adjustment, the ship proceeds on magnetic courses using a gyroscopic or satellite compass and considering magnetic declination. However, non-magnetic compasses are only compulsory for ships of 500 gross tonnage or upwards (SOLAS V/19.2.5.1). Many ships of less than 500 gross tonnage have only a magnetic compass to indicate heading. In these cases, a minimum of five leading lines or a minimum of five bearings of conspicuous and distant points or sun azimuths are necessary to adjust the compass. This makes compass adjustment more laborious and time consuming. To expedite this process, a reliable and practical method was developed to use the courses over ground given by a GNSS receiver and a single visual reference instead of the headings provided by a gyroscopic or satellite compass. The method is valid for all ships, but is primarily intended for those equipped with only a magnetic compass to indicate heading.
Journal Article
How to build a magnetometer with thermal atomic vapor: a tutorial
This article is designed as a step-by-step guide to optically pumped magnetometers based on alkali atomic vapor cells. We begin with a general introduction to atomic magneto-optical response, as well as expected magnetometer performance merits and how they are affected by main sources of noise. This is followed by a brief comparison of different magnetometer realizations and an overview of current research, with the aim of helping readers to identify the most suitable magnetometer type for specific applications. Next, we discuss some practical considerations for experimental implementations, using the case of an M z magnetometer as an example of the design process. Finally, an interactive workbook with real magnetometer data is provided to illustrate magnetometer-performance analysis.
Journal Article
The Effect of Vehicles Attitude Angle Error on Magnetic Compass Heading Estimation
The three-component magnetic sensor is used to measure the heading of the vehicle. Under working, the magnetic sensor be rotated to the horizontal plane according to the attitude angle of the vehicle, and then the heading estimation is performed. However, the vehicle’s attitude angle measurement errors affect the accuracy of the magnetic sensor measurement’s east and north components and then lead to a false heading result. Based on the relation of magnetic field measurement error and magnetic heading error, the effect model of geomagnetic measurement error on magnetic heading error is derived in this paper. Finally, the characteristics of attitude angle errors on magnetic heading are verified by experiments, and the results show that particular angles can avoid the magnetic compass’s effect by the vehicle’s attitude angle error.
Journal Article
Podcast
This week on the Science podcast, Jennifer Golbeck digs into the science of de-extinction with biologist Helen Pilcher and recommends a clinician's compassionate tale of psychosomatic disorders.
Journal Article