Integrating EM and Patch-seq data: Synaptic connectivity and target specificity of predicted Sst transcriptomic types.

Neural circuit function is shaped both by the cell types that comprise the circuit and the connections between those cell types 1 . Neural cell types have previously been defined by morphology 2, 3 , electrophysiology 4, 5 , transcriptomic expression 6-8 , connectivity 9-13 , or even a combination of such modalities 14-16 . More recently, the Patch-seq technique has enabled the characterization of morphology (M), electrophysiology (E), and transcriptomic (T) properties from individual cells 17-20 . Using this technique, these properties were integrated to define 28, inhibitory multimodal, MET-types in mouse primary visual cortex 21 . It is unknown how these MET-types connect within the broader cortical circuitry however. Here we show that we can predict the MET-type identity of inhibitory cells within a large-scale electron microscopy (EM) dataset and these MET-types have distinct ultrastructural features and synapse connectivity patterns. We found that EM Martinotti cells, a well defined morphological cell type 22, 23 known to be Somatostatin positive (Sst+) 24, 25 , were successfully predicted to belong to Sst+ MET-types. Each identified MET-type had distinct axon myelination patterns and synapsed onto specific excitatory targets. Our results demonstrate that morphological features can be used to link cell type identities across imaging modalities, which enables further comparison of connectivity in relation to transcriptomic or electrophysiological properties. Furthermore, our results show that MET-types have distinct connectivity patterns, supporting the use of MET-types and connectivity to meaningfully define cell types.

Movement-related phase locking in the delta-theta frequency band.

Movements result from a complex interplay of multiple brain regions. These regions are assembled into distinct functional networks depending on the specific properties of the action. However, the nature and details of the dynamics of this complex assembly process are unknown. In this study, we sought to identify key markers of the neural processes underlying the preparation and execution of motor actions that always occur irrespective of differences in movement initiation, hence the specific neural processes and functional networks involved. To this end, EEG activity was continuously recorded from 18 right-handed healthy participants while they performed a simple motor task consisting of button presses with the left or right index finger. The movement was performed either in response to a visual cue or at a self-chosen, i.e., non-cued point in time. Despite these substantial differences in movement initiation, dynamic properties of the EEG signals common to both conditions could be identified using time-frequency and phase locking analysis of the EEG data. In both conditions, a significant phase locking effect was observed that started prior to the movement onset in the δ-θ frequency band (2-7Hz), and that was strongest at the electrodes nearest to the contralateral motor region (M1). This phase locking effect did not have a counterpart in the corresponding power spectra (i.e., amplitudes), or in the event-related potentials. Our finding suggests that phase locking in the δ-θ frequency band is a ubiquitous movement-related signal independent of how the actual movement has been initiated. We therefore suggest that phase-locked neural oscillations in the motor cortex are a prerequisite for the preparation and execution of motor actions.

[Image quality of thickened slabs in multislice CT chest examinations: postprocessing vs. direct reconstruction]. / Bildqualität aufaddierter Schichten bei MSCT-Untersuchungen des Thorax: Bildnachverarbeitung versus Direktrekonstruktion.

PURPOSE: Postprocessing offers the possibility of real-time creation of thickened slabs from a set of thin slices. This allows the interactive change from thick to thin slices for better evaluation of unclear lesions. As a result the clinical workflow of MSCT evaluation can be improved. However, to be able to apply this postprocessing software in the clinical routine, degradations in the image quality (compared to standard original reconstructed images) have to be avoided. The purpose of this study was to compare the image quality of thickened slabs from MSCT chest examinations that have either been directly reconstructed from the raw data or have been retrospectively generated via postprocessing. MATERIALS AND METHODS: Chest MSCT examinations of 20 patients (mean age: 56 years) were performed on a 16-slice MSCT scanner (Mx8000IDT16, Philips, Best, Netherlands) using the following scan parameters: 120 kV, 94 effective mAs, 16 x 1.5 mm collimation, 512 x 512 matrix, field of view 371 x 371 mm, CTDIvol = 6.3 mGy, DLP = 210 mGyxcm). Slices with a thickness of 3 and 5 mm were generated for each examination both directly from the raw data and via postprocessing. Corresponding images from postprocessing and direct reconstruction (lung/soft tissue window) were evaluated by two radiologists with respect to 5 criteria on the basis of a five-point scale: organ structure, contour of small objects, contrast, image noise and artifacts. Differences between both data sets regarding image quality were assessed for each of the 5 criteria using a Wilcoxon test with Bonferroni correction. In addition, image noise was analyzed quantitatively in a region of interest in the aorta. RESULTS: For the lung and soft tissue window, both reviewers and all criteria, no differences in image quality were detected between the thickened slices obtained via direct reconstruction and the postprocessing method. In 96 % and 95 % of the cases images of the two reconstruction methods were graded identically for 3 mm and 5 mm slices. In the remaining 4 % and 5 %, the evaluations differed only by one point on the five-point scale. The median grade of the first reviewer was 1 and that of the second reviewer was 2. There were no differences in the quantitative analysis of image noise between both methods. CONCLUSION: The interactive creation of thickened slices is an effective tool for the evaluation of MSCT examinations. For the defined scan parameters in this study there were no differences in image quality between postprocessing methods (e. g. slab viewer) and direct image reconstruction.

Complex dynamics of a single neuron model.

We study a mathematical model of a single neuron with self-coupling. The model is based on the FitzHugh-Nagumo oscillator and an equation describing synaptic properties of the neuron. The analysis of the model is focused on its dynamics, depending on parameters characterizing synaptic time constants and external signals that affect the neuron. Applying Lyapunov exponents and bifurcation analysis, we point out the occurrence of parameter regions with different behavior such as bursting (chaotic or periodic), spiking, and multistable phenomena. Moreover, we can describe the dynamics of the model using an analytical approximation of the one-dimensional Poincaré map extracted from the numerical simulations.

Chaos-hyperchaos transition

The chaos-hyperchaos transition occurs when the second Lyapunov exponent becomes positive. We argue that this transition is mediated by changes in the stability of an infinite number of unstable periodic orbits embedded in the chaotic attractor. Bifurcations of unstable periodic orbits occur in the neighborhood of the chaos-hyperchaos transition point where we observe unstable variable dimensionality. We give evidence that the chaos-hyperchaos transition is initiated by (i) the saddle-repeller bifurcation of a particular unstable periodic orbit usually of low period, (ii) the appearance of a repelling node in the saddle-node bifurcation, after which the chaotic attractor becomes riddled, or (iii) the absorption of the repeller (unstable node or focus) originally located out of the attractor by the growing attractor.