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We present an imaging system for pan-neuronal recording in crawling Caenorhabditis elegans. A spinning disk confocal microscope, modified for automated tracking of the C. elegans head ganglia, simultaneously records the activity and position of ∼80 neurons that coexpress cytoplasmic calcium indicator GCaMP6s and nuclear localized red fluorescent protein at 10 volumes per second. We developed a behavioral analysis algorithm that maps the movements of the head ganglia to the animal's posture and locomotion. Image registration and analysis software automatically assigns an index to each nucleus and calculates the corresponding calcium signal. Neurons with highly stereotyped positions can be associated with unique indexes and subsequently identified using an atlas of the worm nervous system. To test our system, we analyzed the brainwide activity patterns of moving worms subjected to thermosensory inputs. We demonstrate that our setup is able to uncover representations of sensory input and motor output of individual neurons from brainwide dynamics. Our imaging setup and analysis pipeline should facilitate mapping circuits for sensory to motor transformation in transparent behaving animals such as C. elegans and Drosophila larva.C. elegans | Drosophila | calcium imaging | thermotaxis U nderstanding how brain dynamics creates behaviors requires quantifying the flow and transformation of sensory information to motor output in behaving animals. Optical imaging using genetically encoded calcium or voltage fluorescent probes offers a minimally invasive method to record neural activity in intact animals. The nematode Caenorhabditis elegans is particularly ideal for optical neurophysiology owing to its small size, optical transparency, compact nervous system, and ease of genetic manipulation. Imaging systems for tracking the activity of small numbers of neurons have been effective in determining their role during nematode locomotion and navigational behaviors like chemotaxis, thermotaxis, and the escape response (1-6).Recordings from large numbers of interconnected neurons are required to understand how neuronal ensembles carry out the systematic transformations of sensory input into motor patterns that build behavioral decisions.Several methods for fast 3D imaging of neural activity in a fixed imaging volume have been developed for different model organisms (7)(8)(9)(10)(11)(12)(13)(14). High-speed light sheet microscopy, light field microscopy, multifocus microscopy, and two-photon structured illumination microscopy have proved effective for rapidly recording large numbers of neurons in immobilized, intact, transparent animals like larval zebrafish and nematodes (15)(16)(17)(18)(19). However, these methods are problematic when attempting to track many neurons within the bending and moving body of a behaving animal. Panneuronal recording in moving animals poses higher demands on spatial and temporal resolution. Furthermore, extracting neuronal signals from recordings in a behaving animal requires an effective analysis pipel...

Summary: Quantum dots, used as local thermometers, detect upstream heat transport in a ν = 2/3 fractional quantum Hall edge state, even when the state is carrying no net charge. AbstractA system of electrons in two dimensions and strong magnetic fields can be tuned to create a gapped 2D system with one dimensional channels along the edge. Interactions among these edge modes can lead to independent transport of charge and heat, even in opposite directions. Measuring the chirality and transport properties of these charge and heat modes can reveal otherwise hidden structure in the edge. Here, we heat the outer edge of such a quantum Hall system using a quantum point contact. By placing quantum dots upstream and downstream along the edge of the heater, we can measure both the chemical potential and temperature of that edge to study charge and heat transport, respectively. We find that charge is transported exclusively downstream, but heat can be transported upstream when the edge has additional structure related to fractional quantum Hall physics.When a two-dimensional electron system (2DES) is subject to a strong perpendicular magnetic field and tuned such that the ratio of electrons to magnetic flux quanta in the system (ν) is near certain integer or fractional values, the bulk of the system develops a gap due to either quantization of kinetic energy (the integer quantum Hall, or IQH, effect) or strong correlations arising from non-perturbative Coulomb interactions (the fractional quantum Hall, or FQH, effect) [1]. While the bulk (2D) is gapped and incompressible, the edge (1D) of the system contains compressible regions with gapless excitations that carry charge chirally around the system, in a direction determined by the external magnetic field. Compressible edge states have gained more attention recently due to their ability to serve as a bus for quasiparticles that exist in exotic FQH phases [2,3]. These edges, however, can have considerable internal structure that is not apparent from bulk transport measurements.The spatial structure of edges is dictated by the interplay between the external confining potential which defines the edge, an additional harmonic confinement from the magnetic field, and Coulomb interactions. It was predicted [4] and verified [5, 6, 7] that for a smooth, topgate-defined confining potential, it is energetically favorable for the electron density to redistribute slightly to create alternating compressible and incompressible strips. This has the effect of spatially separating edges corresponding to different filling factors. Such an effect is not present in sharper edges [8].Perhaps more surprising than this spatial structure is the possibility of modes that carry energy (or heat) upstream, even as the magnetic field carries the injected charge downstream. The edge of the ν = 2/3 FQH state was originally predicted to consist of a ν = 1 edge of electrons going downstream with a ν = 1/3 edge of holes going upstream [9,10] would be allowed to travel diffusively upstream and downstream, l...

The nematode Caenorhabditis elegans navigates toward a preferred temperature setpoint (T s ) determined by long-term temperature exposure. During thermotaxis, the worm migrates down temperature gradients at temperatures above T s (negative thermotaxis) and performs isothermal tracking near T s . Under some conditions, the worm migrates up temperature gradients below T s (positive thermotaxis). Here, we analyze positive and negative thermotaxis toward T s to study the role of specific neurons that have been proposed to be involved in thermotaxis using genetic ablation, behavioral tracking, and calcium imaging. We find differences in the strategies for positive and negative thermotaxis. Negative thermotaxis is achieved through biasing the frequency of reorientation maneuvers (turns and reversal turns) and biasing the direction of reorientation maneuvers toward colder temperatures. Positive thermotaxis, in contrast, biases only the direction of reorientation maneuvers toward warmer temperatures. We find that the AFD thermosensory neuron drives both positive and negative thermotaxis. The AIY interneuron, which is postsynaptic to AFD, may mediate the switch from negative to positive thermotaxis below T s . We propose that multiple thermotactic behaviors, each defined by a distinct set of sensorimotor transformations, emanate from the AFD thermosensory neurons. AFD learns and stores the memory of preferred temperatures, detects temperature gradients, and drives the appropriate thermotactic behavior in each temperature regime by the flexible use of downstream circuits.N avigational behaviors provide a framework for exploring the interplay among sensorimotor circuits, learning, and memory. During a navigational task, animals eventually reach their goals by implementing strategies composed of sensorimotor rules. Experience can modify navigational goals, so memory can also be integrated into sensorimotor pathways. Studying navigation in the nematode Caenorhabditis elegans offers the possibility of understanding the plasticity and programming of sensorimotor circuits from input to output in a small nervous system (1).Previous studies established C. elegans thermotaxis as a model for experience-dependent navigation (2-6). When worms are exposed to specific temperatures between 15°C and 25°C for at least 4 h, they adopt those temperatures as their thermotactic setpoint (T s ) (2, 3, 5, 7). When placed on a spatial temperature gradient, worms seek the T s . When arriving near T s , worms track isotherms. Genetic analysis of thermotaxis has yielded mutants that are athermotactic (crawling randomly on temperature gradients), cryophilic (crawling to the coldest point on a temperature gradient irrespective of T s ), or thermophilic (crawling to the warmest point on a temperature gradient). This observation led to the suggestion that thermotaxis might involve separate circuits for negative thermotaxis (movement down gradients) and positive thermotaxis (movement up gradients) that balance near T s (2, 4).Systematic laser ablation a...

Electrons moving in two dimensions under the influence of strong magnetic fields effectively lose their kinetic energy and display exotic behaviour dominated by Coulomb forces. When the ratio of electrons to magnetic flux quanta in the system (ν) is near 5/2, the electrons are predicted to condense into a correlated phase with fractionally charged quasiparticles and a ground-state degeneracy that grows exponentially as these quasiparticles are introduced. The only way for electrons to transform between the many ground states would be to braid the fractional excitations around each other. This property has been proposed as the basis of a fault-tolerant quantum computer. Here we present observations of localized quasiparticles at ν = 5/2, confined to puddles by disorder. Using a local electrometer to compare how quasiparticles at ν = 5/2 and ν = 7/3 charge these puddles, we were able to extract the ratio of local charges for these states. Averaged over several disorder configurations and samples, we found the ratio to be 4/3, suggesting that the local charges are = e/3 and = e/4, where e is the charge of an electron. This is in agreement with theoretical predictions for a paired state at ν = 5/2. Confirming the existence of localized e/4 quasiparticles shows that proposed interferometry experiments to test statistics and computational ability of the state at ν = 5/2 would be possible.