How do animals adaptively integrate innate with learned behavioral tendencies? We tackle this question using chemotaxis as a paradigm. Chemotaxis in the Drosophila larva largely results from a sequence of runs and oriented turns. Thus, the larvae minimally need to determine (i) how fast to run, (ii) when to initiate a turn, and (iii) where to direct a turn. We first report how odor-source intensities modulate these decisions to bring about higher levels of chemotactic performance for higher odor-source intensities during innate chemotaxis. We then examine whether the same modulations are responsible for alterations of chemotactic performance by learned odor "valence" (understood throughout as level of attractiveness). We find that run speed (i) is neither modulated by the innate nor by the learned valence of an odor. Turn rate (ii), however, is modulated by both: the higher the innate or learned valence of the odor, the less often larvae turn whenever heading toward the odor source, and the more often they turn when heading away. Likewise, turning direction (iii) is modulated concordantly by innate and learned valence: turning is biased more strongly toward the odor source when either innate or learned valence is high. Using numerical simulations, we show that a modulation of both turn rate and of turning direction is sufficient to account for the empirically found differences in preference scores across experimental conditions. Our results suggest that innate and learned valence organize adaptive olfactory search behavior by their summed effects on turn rate and turning direction, but not on run speed. This work should aid studies into the neural mechanisms by which memory impacts specific aspects of behavior.

We report magnetic quantum oscillations measured using torque magnetisation in the Kondo insulator YbB and discuss the potential origin of the underlying Fermi surface. Observed quantum oscillations as well as complementary quantities such as a finite linear specific heat capacity in YbB exhibit similarities with the Kondo insulator SmB, yet also crucial differences. Small heavy Fermi sections are observed in YbB with similarities to the neighbouring heavy fermion semimetallic Fermi surface, in contrast to large light Fermi surface sections in SmB which are more similar to the conduction electron Fermi surface. A rich spectrum of theoretical models is suggested to explain the origin across different Kondo insulating families of a bulk Fermi surface potentially from novel itinerant quasiparticles that couple to magnetic fields, yet do not couple to weak DC electric fields.

A central question in the underdoped cuprates pertains to the nature of the pseudogap ground state. A conventional metallic ground state of the pseudogap region has been argued to host quantum oscillations upon destruction of the superconducting order parameter by modest magnetic fields. Here, we use low applied measurement currents and millikelvin temperatures on ultrapure single crystals of underdoped YBa2Cu3O6+x to unearth an unconventional quantum vortex matter ground state characterized by vanishing electrical resistivity, magnetic hysteresis, and nonohmic electrical transport characteristics beyond the highest laboratory-accessible static fields. A model of the pseudogap ground state is now required to explain quantum oscillations that are hosted by the bulk quantum vortex matter state without experiencing sizable additional damping in the presence of a large maximum superconducting gap; possibilities include a pair density wave.

Abstract:The trigeminal sensory system is unique in its innervation of structures specific to the orofacial area. Nociceptive trigeminal afferents are known to synapse with second-order neurons in the trigeminal subnucleus caudalis (Sp5C) in the brain stem. The activity of neurons within the Sp5C is responsible for the relay of nociceptive signals to higher brain centers. Recent evidence suggests that central sensitization may be fundamental to many trigeminal-specific painful neuropathies, including trigeminal neuralgia and migraine.Glia within the Sp5C are emerging as prime suspects in trigeminal central sensitization. In particular, microglial activation has been implicated in the development of neuropathic pain. It is possible that activated microglia release factors that alter the activity of second-order neurons or the synaptic activity of peripheral terminals within the Sp5C.Microglial activation has been characterized by changes in morphology, expression of membrane receptors and ion channels, as well as alterations to cytokine and chemokine release. In addition, microglia have been studied in brain slice and dissociated culture where activation is characterized by changes to P2X receptor and potassium channel membrane currents. However, little is known about resting and activated microglial membrane properties in the Sp5C and, furthermore, how these properties are affected following trigeminal nerve injury. This review summarizes the anatomical and pathophysiological importance of the Sp5C and focuses on recent studies on neurons and microglia in the trigeminal sensory system. The final part of the review aims to link important aspects of microglial membrane physiology with their potential role in chronic trigeminal pain conditions.

The nature of the Fermi surface observed in the recently discovered family of unconventional insulators starting with SmB6 is a subject of intense inquiry. Here we shed light on this question by accessing quantum oscillations in the high magnetic field-induced metallic regime above ≈47 T in YbB12, which we compare with the unconventional insulating regime. In the field-induced metallic regime, we find prominent quantum oscillations in the electrical resistivity characterised by multiple frequencies and heavy effective masses. The close similarity in Lifshitz-Kosevich low-temperature growth of quantum oscillation amplitude in insulating YbB12 to field-induced metallic YbB12, points to an origin of quantum oscillations in insulating YbB12 from in-gap neutral low energy excitations. Higher frequency Fermi surface sheets of heavy quasiparticle effective mass emerge in the field-induced metallic regime of YbB12 in addition to multiple heavy Fermi surface sheets observed in both insulating and metallic regimes. f-electron hybridisation is thus observed to persist from the unconventional insulating to the field-induced metallic regime of YbB12, in contrast to the unhybridised conduction electron Fermi surface observed in unconventional insulating SmB6. Our findings thus require an alternative model for YbB12, of neutral in-gap low energy excitations, wherein the f-electron hybridisation is retained.

Errors arising from the under- and overfilling of cone-plate geometries have been investigated for combinations of smooth and micro-roughened cone-plate geometries. We observed experimentally that 0.1 ml deviations in the loading volume, such as can occur due to subjective filling or evaporation, will proportionally change the measured viscosity by 2–3%. We also give a simple method to avoid these errors during routine measurements.

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Cell-to-cell interactions between the immune and nervous systems are increasingly recognized for their importance in health and disease. Assessment of cellular neuro-immune interactions can be aided by coculture of two (or more) cells in an in vitro model system that preserves the morphology of neuronal cells. Here we describe methods to investigate the cytotoxic effector functions of natural killer cells on sensory neurons isolated from syngeneic embryonic and adult mice. We present methods for the morphological analysis of axon fragmentation (pruning) and dynamic cell function via live confocal calcium imaging. These techniques can easily be adapted to study interactions between other combinations of immune cell subsets and neuronal populations.