Fluidity of functional ensembles in the infralimbic cortex of rats during reward seeking

The medial prefrontal cortex (mPFC), specifically the prelimbic (PL) and the infralimbic region (IL), plays a crucial role during reward seeking behaviour. The IL specifically is involved in the control of reward seeking and has been implicated in the representation of different rewards. However, the precise representation of reward seeking behaviour on a neuronal network level within the IL remains elusive. To investigate neuronal ensembles during reward seeking in the IL of the mPFC in rats, an operant conditioning paradigm was combined with imaging of the intracellular calcium concentration ([Ca2+]i) as a proxy for neuronal activity. The latter is achieved using GRIN lenses and miniaturized head-mounted fluorescence microscopes. A frame trigger was used to synchronize the operant conditioning chambers with the [Ca2+]i data and an analysis pipeline was developed using a combination of custom designed Matlab classes and available open source software. Neurons were identified for three saccharin self-administration (SA) and one reinstatement (RE) session and then matched across sessions. Periods during which rats interacted with the operant conditioning setup were identified (e.g. lever presses and head entries into the reward port) and the corresponding [Ca2+]i transients were used to identify neurons coactive during distinct phases of reward seeking behaviour. Neurons were classified according to the time point of their activity relative to the sequence of actions consisting of the lever press and the time before, during, and after the head entry. This analysis revealed that subsets of neurons are preferentially active during distinct events of the reward seeking. Also, cells tuned to time points during the reward seeking did not appear or show tuning in all of the sessions. If they did show tuning, however, the phase of the reward seeking to which they showed tuning generally remained the same. Hence, the specific ensemble which is active during the reward seeking in each session changes. Individual neurons that are recruited into these ensembles, however, keep their tuning. Also, the composition of tuned neurons active during a specific behavioural phase remains stable. In addition, neurons that are active and tuned in multiple sessions do not appear to be arranged in a topology that can be identified with the methods used. In conclusion, the sequence of the reward seeking behaviour is encoded in neuronal ensembles of the IL cortex. These ensembles are formed from a larger pool of available neurons in each session. Neurons participating in these ensembles preferentially keep their tuning to a phase of the reward seeking, but may not be recruited to each of the ensembles. Thus, ensembles representing identical behavioural episodes in different sessions are not stable, but fluidly change their composition

A New Stapes-Head Coupler for the Vibrant Soundbridge System

Introduction: The Vibrant Soundbridge (MED-EL Medical Electronics, Austria) is an active middle ear implant with a floating mass transducer (FMT) for patients with conductive, sensorineural, or mixed hearing loss. While the FMT is vertically aligned above the stapes head (SH) with the current Vibroplasty Clip coupler (MED-EL Medical Electronics), the new SH coupler was developed to mount the FMT on the inferior side of the stapes and to fit in the reduced middle ear space after canal-wall-down mastoidectomy. Methods: Using 11 human cadaveric temporal bones (TBs), placements of the new SH couplers on the stapes were examined, and effective stimuli to the cochlea were evaluated by measuring piston-like motion of the stapes footplate with a current of 1 mA on the FMT. The results were assessed in comparison with the Vibroplasty Clip coupler. Results: The new SH coupler showed perfect coupling on the stapes in 9 out of 11 TBs. A small gap between the SH and the plate of the connection link part was unavoidable in 2 TBs but had negligible effect on vibrational motion of the stapes. Vibrational motion of the stapes with the new SH coupler was reduced at frequencies above 3 kHz compared to the corresponding motion with the current Vibroplasty Clip coupler, but the relative attenuation over all 11 cadaveric temporal bones was <10 dB. Conclusions: The new SH coupler provides an alternative with more stable fixation when placement of the current Vibroplasty Clip coupler is limited due to insufficient space after canal-wall-down mastoidectomy, while still delivering effective stimuli to the cochlea

Diversity of layer 5 projection neurons in the mouse motor cortex

In the primary motor cortex (M1), layer 5 projection neurons signal directly to distant motor structures to drive movement. Despite their pivotal position and acknowledged diversity these neurons are traditionally separated into broad commissural and corticofugal types, and until now no attempt has been made at resolving the basis for their diversity. We therefore probed the electrophysiological and morphological properties of retrogradely labeled M1 corticospinal (CSp), corticothalamic (CTh), and commissural projecting corticostriatal (CStr) and corticocortical (CC) neurons. An unsupervised cluster analysis established at least four phenotypes with additional differences between lumbar and cervical projecting CSp neurons. Distinguishing parameters included the action potential (AP) waveform, firing behavior, the hyperpolarisation-activated sag potential, sublayer position, and soma and dendrite size. CTh neurons differed from CSp neurons in showing spike frequency acceleration and a greater sag potential. CStr neurons had the lowest AP amplitude and maximum rise rate of all neurons. Temperature influenced spike train behavior in corticofugal neurons. At 26°C CTh neurons fired bursts of APs more often than CSp neurons, but at 36°C both groups fired regular APs. Our findings provide reliable phenotypic fingerprints to identify distinct M1 projection neuron classes as a tool to understand their unique contributions to motor function

Erratum: Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory

We present a combined fit of a simple astrophysical model of UHECR sources to both the energy spectrum and mass composition data measured by the Pierre Auger Observatory. The fit has been performed for energies above 5 ⋅ 10(18) eV, i.e. the region of the all-particle spectrum above the so-called ankle feature. The astrophysical model we adopted consists of identical sources uniformly distributed in a comoving volume, where nuclei are accelerated through a rigidity-dependent mechanism. The fit results suggest sources characterized by relatively low maximum injection energies, hard spectra and heavy chemical composition. We also show that uncertainties about physical quantities relevant to UHECR propagation and shower development have a non-negligible impact on the fit results

An Indication of anisotropy in arrival directions of ultra-high-energy cosmic rays through comparison to the flux pattern of extragalactic gamma-ray sources

International audienceA new analysis of the data set from the Pierre Auger Observatory provides evidence for anisotropy in the arrival directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals from strong, nearby sources. The data consist of 5514 events above with zenith angles up to 80° recorded before 2017 April 30. Sky models have been created for two distinct populations of extragalactic gamma-ray emitters: active galactic nuclei from the second catalog of hard Fermi-LAT sources (2FHL) and starburst galaxies from a sample that was examined with Fermi-LAT. Flux-limited samples, which include all types of galaxies from the Swift-BAT and 2MASS surveys, have been investigated for comparison. The sky model of cosmic-ray density constructed using each catalog has two free parameters, the fraction of events correlating with astrophysical objects, and an angular scale characterizing the clustering of cosmic rays around extragalactic sources. A maximum-likelihood ratio test is used to evaluate the best values of these parameters and to quantify the strength of each model by contrast with isotropy. It is found that the starburst model fits the data better than the hypothesis of isotropy with a statistical significance of 4.0σ, the highest value of the test statistic being for energies above . The three alternative models are favored against isotropy with 2.7σ–3.2σ significance. The origin of the indicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed