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In vivo calcium imaging has become a method of choice to image neuronal population activity throughout the nervous system. These experiments generate large sequences of images. Their analysis is computationally intensive and typically involves motion correction, image segmentation into regions of interest (ROIs), and extraction of fluorescence traces from each ROI. Out of focus fluorescence from surrounding neuropil and other cells can strongly contaminate the signal assigned to a given ROI. In this study, we introduce the FISSA toolbox (Fast Image Signal Separation Analysis) for neuropil decontamination. Given pre-defined ROIs, the FISSA toolbox automatically extracts the surrounding local neuropil and performs blind-source separation with non-negative matrix factorization. Using both simulated and in vivo data, we show that this toolbox performs similarly or better than existing published methods. FISSA requires only little RAM, and allows for fast processing of large datasets even on a standard laptop. The FISSA toolbox is available in Python, with an option for MATLAB format outputs, and can easily be integrated into existing workflows. It is available from Github and the standard Python repositories.

Neural oscillations are ubiquitously observed in cortical activity, and are widely believed to be crucial for mediating transmission of information across the cortex. Yet, the neural phenomena contributing to each oscillation band, and their effect on information coding and transmission, are largely unknown. Here, we investigated whether individual frequency bands specifically reflect changes in the concentrations of dopamine, an important neuromodulator, and how dopamine affects oscillatory information processing. We recorded the local field potential (LFP) at different depths of primary visual cortex (V1) in anesthetized monkeys (Macaca mulatta) during spontaneous activity and during visual stimulation with Hollywood movie clips while pharmacologically mimicking dopaminergic neuromodulation by systemic injection of L-DOPA (a metabolic precursor of dopamine). We found that dopaminergic neuromodulation had marked effects on both spontaneous and movie-evoked neural activity. During spontaneous activity, dopaminergic neuromodulation increased the power of the LFP specifically in the [19-38 Hz] band, suggesting that the power of endogenous visual cortex oscillations in this band can be used as a robust marker of dopaminergic neuromodulation. Moreover, dopamine increased visual information encoding over all frequencies during movie stimulation. The information increase due to dopamine was prominent in the supragranular layers of cortex that project to higher cortical areas and in the gamma [50-100 Hz] band that has been previously implicated in mediating feedforward information transfer. These results thus individuate new neural mechanisms by which dopamine may promote the readout of relevant sensory information by strengthening the transmission of information from primary to higher areas.

Cortical responses to sensory stimuli are modulated by behavioral state. In the primary visual cortex (V1), visual responses of pyramidal neurons increase during locomotion. This response gain was suggested to be mediated through inhibitory neurons, resulting in the disinhibition of pyramidal neurons. Using in vivo two-photon calcium imaging in layers 2/3 and 4 in mouse V1, we reveal that locomotion increases the activity of vasoactive intestinal peptide (VIP), somatostatin (SST) and parvalbumin (PV)-positive interneurons during visual stimulation, challenging the disinhibition model. In darkness, while most VIP and PV neurons remained locomotion responsive, SST and excitatory neurons were largely non-responsive. Context-dependent locomotion responses were found in each cell type, with the highest proportion among SST neurons. These findings establish that modulation of neuronal activity by locomotion is context-dependent and contest the generality of a disinhibitory circuit for gain control of sensory responses by behavioral state.

Cortical responses to sensory stimuli are modulated by behavioral state. In the primary visual cortex (V1), visual responses of pyramidal neurons increase during locomotion. This response gain was suggested to be mediated through inhibitory neurons, resulting in the disinhibition of pyramidal neurons. Using in vivo two-photon calcium imaging in layers 2/3 and 4 in mouse V1, we reveal that locomotion increases the activity of vasoactive intestinal peptide (VIP), somatostatin (SST) and parvalbumin (PV)-positive interneurons during visual stimulation, challenging the disinhibition model. In darkness, while most VIP and PV neurons remained locomotion responsive, SST and excitatory neurons were largely non-responsive. Context-dependent locomotion responses were found in each cell type, with the highest proportion among SST neurons. These findings establish that modulation of neuronal activity by locomotion is context-dependent and contest the generality of a disinhibitory circuit for gain control of sensory responses by behavioral state. DOI: http://dx.doi.org/10.7554/eLife.14985.001, eLife digest How we perceive what we see depends on the context in which we see it, such as what we are doing at the time. For example, we perceive a park landscape differently when we are running through it than when we are sitting on a park bench. Behavior can also alter neuronal responses in the brain. Indeed, the neurons in the part of the brain that receives information related to vision (known as the visual cortex) respond differently to visual stimuli when an animal is moving compared to when the animal is still. However, while some recent studies revealed that specific types of neurons become more or less responsive during movement, others reported the opposite results. One hypothesis that would explain these contradictory findings would be if the way that behavior, in this case movement, affects neuronal responses also depends on the external context in which the movement happens. Now, Pakan et al. have tested this hypothesis by imaging the activity of different types of neurons in the primary visual cortex of mice that were either running on a treadmill or staying still. The experiments were conducted in two different contexts: in total darkness (in which the mice could not see) and in the presence of display screens (which provided the mice with visual stimulation). Pakan et al. confirmed that running does indeed affect the activity of specific neurons in different ways in different contexts. For example, when the mice received visual stimulation, the three main classes of neurons that send inhibitory signals in the visual cortex became more active during running. However, when the mouse ran in the dark, two of these neuron types became more active during running while the third type of neuron was unresponsive. This finding reveals more about the dynamic nature of inhibitory activity that strongly depends on the animal’s behaviour. It also shows how these neurons influence the excitatory neurons in the visual cortex, which send information to the rest of the brain for further processing towards perception. The next step will be to identify what precise mechanism makes these neurons respond differently in unique contexts, and to tease apart how these movement-dependent signals affect the way animals perceive visual stimuli. DOI: http://dx.doi.org/10.7554/eLife.14985.002

‘Bah! Humbug!’ It's the most famous line in Charles Dickens' A Christmas Carol, but is it the most important? Surely not, for this Christmas classic is not centrally about Christmas, but about a man, the holiday being the convenient setting for his transformation. What kind of transformation? Why a moral transformation of course, because the man, Ebenezer Scrooge, through multiple encounters with the spirit world, becomes a good man by the end of the story. But where does this story begin, what are we to think of Scrooge at the outset and how is his transformation accomplished? These are the questions I take up here, for while Scrooge is tightfisted, covetous and hard-hearted, he is still a man of principle. Judged by the standards of some views on ethics, Scrooge isn't actually all that bad. How can that be? Let's start with a quick overview of two centuries of ethical theory.

Distributed neural processing likely entails the capability of networks to reconfigure dynamically the directionality and strength of their functional connections. Yet, the neural mechanisms that may allow such dynamic routing of the information flow are not yet fully understood. We investigated the role of gamma band (50–80 Hz) oscillations in transient modulations of communication among neural populations by using measures of direction-specific causal information transfer. We found that the local phase of gamma-band rhythmic activity exerted a stimulus-modulated and spatially-asymmetric directed effect on the firing rate of spatially separated populations within the primary visual cortex. The relationships between gamma phases at different sites (phase shifts) could be described as a stimulus-modulated gamma-band wave propagating along the spatial directions with the largest information transfer. We observed transient stimulus-related changes in the spatial configuration of phases (compatible with changes in direction of gamma wave propagation) accompanied by a relative increase of the amount of information flowing along the instantaneous direction of the gamma wave. These effects were specific to the gamma-band and suggest that the time-varying relationships between gamma phases at different locations mark, and possibly causally mediate, the dynamic reconfiguration of functional connections., This study reveals the presence of gamma-frequency travelling waves, which appear to dynamically route the flow of information within the visual cortex., Author Summary Complex and flexible behavior likely results from the ability of groups of neurons in the brain to reconfigure dynamically the information flow across different brain areas, depending on what the brain is engaged in (processing a stimulus or carrying out a task). Here, we investigate how oscillations of cortical activity in the gamma frequency range (50–80 Hz) may influence dynamically the direction and strength of information flow across different groups of neurons. By recording neural activity and measuring information flow between multiple locations in visual cortex during the presentation of Hollywood movies, we found that the arrangement of the phase of gamma oscillations at different locations indicated the presence of waves propagating along the cortical tissue. These waves were observed to propagate along the direction with the maximal flow of information transmitted between neural populations. The gamma waves changed direction during presentation of different movie scenes, and when this happened, the strength of information flow in the direction of the gamma wave propagation was transiently reinforced. These findings suggest that the propagation of gamma oscillations may reconfigure dynamically the directional flow of cortical information during sensory processing.

De plus en plus, le communautarisme apparait dans les manuels d'enseignement de philosophie politique. Cette theorie entrant dans le contenu des cours d'ethique, de philosophie sociale et politique apporte, selon l'A., une critique importante et interessante du liberalisme qui permet de mieux comprendre les hypotheses des theoriciens liberaux comtemporains. L'A. decrit la methode qu'il a utilisee pour enseigner le communautarisme

Foreword: Joining the Manger to the Sleigh? ( Stephen Nissenbaum). Editor's Introduction (Scott C. Lowe). Part I: Christmas: In the Beginning. 1. Jesus, Mary and Hume: On the Possibility of the Virgin Birth (Zachary Jurgensen and Jason Southworth). 2. The Virgin Birth: Authentic Christmas Magic (Victor Lyons). 3. Putting the "Yule" Back in "Yuletide" (Todd Preston). Part II: Is Celebrating Christmas Really a Good Idea? 4. Armed for the War on Christmas (Scott F. Aiken). 5. Christmas Mythologies: Sacred and Secular (Guy Bennett-Hunter). 6. The Significance of Christmas for Liberal Multiculturalism (Mark Mercer). 7. Crummy Commercials and BB Guns: Son-of-a-Bitch Consumerism in a Christmas Classic (Erin Haire and Dustin Nelson). Part III: Santa: A Deeper Look. 8. The Mind of Santa Claus and the Metaphors He Lives By (William E. Deal and S. Waller). 9. Making a List, Checking It Twice: The Santa Claus Surveillance System (Richard Hancuff and Noreen O'Connor). 10. You'd Better Watch Out... (Will Williams). 11. Santa's Sweatshop: Elf Exploitation for Christmas (Matthew Brophy). Part IV: The Morality of Christmas. 12. Against the Santa Clause Lie: The Truth We Should Tell Our Children (David Kyle Johnson). 13. Lying to Children about Santa: Why It's Just Not Wrong (Era Gavrielides). 14. Putting Claus Back into Christmas (Steven D. Hales). 15. Scrooge Learns it All in One Night: Happiness and the Virtues of Christmas (Dane Scott). Part V: Christmas Through Others' Eyes. 16. Holly Jolly Atheists: A Naturalistic Justification for Christmas (Ruth Tallman). 17. Heaven, Hecate and Hallmark: Christmas in Hindsight (Marion G. Mason). 18. Festivus and the Need for Seasonal Absurdity (Caleb Holt). 19. Common Claus: Santa as Cross-Cultural Connection (Cindy Scheopner). Afterword (Santa Claus). Notes on Contributors (Santa's Elves).

When an individual repeatedly performs a simple sensory task, such as discrimination between similar visual stimuli, performance gradually increases until it asymptotically approaches saturation. This phenomenon is known as perceptual learning, however the neural correlates of this process are not well understood. Here we consider the results of an experiment in perceptual learning of visual contrast discrimination in cortical areas V1 and V4. In the experiment, a Gabor (V4 recordings) or sinusoidal (V1 recordings) stimulus, with a contrast chosen at random from a set of 14 possibilities, was presented to a macaque monkey. Recordings were made using chronically implanted electrodes in a multi-unit array. The animal was tasked with determining whether the contrast was higher or lower than a control stimulus of 30% contrast, and a correct response was met with a water reward. Experimentation continued for ~20 days until performance saturated. A population-wide linear-discriminant decoding technique based on the mean firing rates during 500ms of stimulus presentation from ~20 channels in V4 was found to achieve similar levels of performance at completing the discrimination task, and to yield a similar rate of improvement in performance, as the monkey's behavioural responses. However, the same analysis in V1 found decoder performance was the same throughout the learning process, despite the animal's improvement in performance. This suggests contrast information present in V1 remains consistent throughout learning, whilst V4 improves in its ability to readout this information from V1.