We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the solar system, exploring the transient optical sky, and mapping the Milky Way. LSST will be a large, wide-field ground-based system designed to obtain repeated images covering the sky visible from Cerro Pachón in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg 2 field of view, a 3.2-gigapixel camera, and six filters (ugrizy) covering the wavelength range 320-1050 nm. The project is in the construction phase and will begin regular survey operations by 2022. About 90% of the observing time will be devoted to a deep-wide-fast survey mode that will uniformly observe a 18,000 deg 2 region about 800 times (summed over all six bands) during the anticipated 10 yr of operations and will yield a co-added map to r∼27.5. These data will result in databases including about 32 trillion observations of 20 billion galaxies and a similar number of stars, and they will serve the majority of the primary science programs. The remaining 10% of the observing time will be allocated to special projects such as Very Deep and Very Fast time domain surveys, whose details are currently under discussion. We illustrate how the LSST science drivers led to these choices of system parameters, and we describe the expected data products and their characteristics.

Chiral odor pairs initially smelling the same become perceptually distinct following aversive Pavlovian conditioning, in parallel with spatial divergence of odor activity patterns in human olfactory (piriform) cortex, highlighting critical behavioral advantages when associative learning is accompanied by improved perceptual analysis of danger-predicting sensory signals.Learning to associate sensory cues with threats is critical for minimizing aversive experience. The ecological benefit of associative learning relies upon accurate perception of predictive cues, but how aversive learning enhances perceptual acuity of sensory signals, particularly in humans, is unclear. We combined multivariate functional magnetic resonance imaging with olfactory psychophysics to show that initially indistinguishable odor enantiomers (mirrorimage molecules) become discriminable following aversive conditioning, paralleling spatial divergence of ensemble activity patterns in primary olfactory (piriform) cortex. Our findings indicate that aversive learning induces piriform plasticity with corresponding gains in odor enantiomer discrimination, underscoring the capacity of fear conditioning to update perceptual representation of predictive cues, over and above its well-recognized role in the acquisition of conditioned responses. That completely indiscriminable sensations can be transformed into discriminable percepts further accentuates the potency of associative learning to enhance sensory cue perception and support adaptive behavior.The ability to minimize contact with aversive experience is a hallmark of adaptive behavior. Via mechanisms of associative learning, organisms can use sensory information in the environment to predict impending danger and initiate fight-or-flight responses. The behavioral efficacy of associative learning thus hinges upon sensitive and accurate perceptual evaluation of sensory signals. In particular, the ability to discriminate between biologically meaningful cues (e.g., smell of a 175kg lion) and similar but irrelevant stimuli (e.g., smell of a 3kg housecat) maximizes an organism's response sensitivity while minimizing hypervigilant and impulsive behaviors.However, models of associative learning have traditionally focused on delineating the formation of associations between a sensory cue (the conditioned stimulus, or CS) and a

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Efficient recognition of odorous objects universally shapes animal behavior and is crucial for survival. To distinguish kin from non-kin, mate from non-mate, food from non-food, organisms must be able to create meaningful perceptual representations of odor qualities and categories. It is currently unknown where, and in what form, the brain encodes information about odor quality. By combining functional magnetic resonance imaging (fMRI) with multivariate (pattern-based) techniques, we show that spatially distributed ensemble activity in human posterior piriform cortex (PPC) coincides with perceptual ratings of odor quality, such that odorants with more (or less) similar fMRI patterns were perceived as more (or less) alike. Critically, these effects were not observed in anterior piriform cortex, amygdala, or orbitofrontal cortex, demonstrating that ensemble coding of odor categorical perception is regionally specific for PPC. These findings substantiate theoretical models emphasizing the importance of distributed piriform templates for the perceptual reconstruction of odor object quality.A key property of the brain is to create coherent, meaningful perceptual constructs from the complexity of the outside world. These internalized representations of the external environment provide a neural basis for object recognition, identification, and categorization, enabling organisms to focus cognitive resources, optimize behavioral responses, and generalize past experiences to novel events 1,2 .Research on object processing has traditionally focused on visual object processing 2,3 , which tends to overshadow the critical ecological role of "odor objects" -here defined as the perceptual quality or character of a smell emitted from an odorous substance. Efficient

Nervous systems must encode information about the identity of expected outcomes to make adaptive decisions. However, the neural mechanisms underlying identity-specific value signaling remain poorly understood. By manipulating the value and identity of appetizing food odors in a pattern-based imaging paradigm of human classical conditioning, we were able to identify dissociable predictive representations of identity-specific reward in orbitofrontal cortex (OFC) and identity-general reward in ventromedial prefrontal cortex (vmPFC). Reward-related functional coupling between OFC and olfactory (piriform) cortex and between vmPFC and amygdala revealed parallel pathways that support identityspecific and -general predictive signaling. The demonstration of identity-specific value representations in OFC highlights a role for this region in model-based behavior and reveals mechanisms by which appetitive behavior can go awry.reward value | associative learning | ventromedial prefrontal cortex | olfaction | multivoxel pattern analysis P redictive representations of future outcomes are critical for guiding adaptive behavior. To choose different types of rewards, such as food, shelter, and mates, it is essential that predictive signals contain specific information about the identity of those outcomes. Food rewards differ dramatically in their nutritional composition, and identity-specific cues allow differential foraging depending on current needs of the organism. The absence of precise mappings between predictive reward signals and their intended outcomes would have devastating effects on foodbased decisions.Despite the ecological relevance of outcome-specific predictive coding, which can be observed even in Drosophila (1), most research in human and nonhuman primates has focused on "common currency" signals of economic values in the orbitofrontal cortex (OFC) (2, 3) and ventromedial prefrontal cortex (vmPFC) (4-8). These signals, which by definition are independent of the specific nature of the reward, can be used to compare and choose between alternative outcomes, but are unable to inform expectations about the specific identity of the outcome. For this, identity-specific representations that conjointly represent information about both affective value (how good is it?) and outcome identity (what is it?) are necessary. Recent data suggest that the OFC is involved in signaling information about specific outcomes (9-14). For instance, many OFC neurons signal both the value and the identity of the predicted outcome (12), and OFC lesions diminish the effects of outcome identity (but not general affective value) on conditioned behavior (13).Recent imaging work has also begun to address how the human brain encodes predictive information about rewarding outcomes. One study (9) used a functional magnetic resonance imaging (fMRI) adaptation paradigm to provide evidence for identity-based codes for reward in the OFC. Another investigation (4) used fMRI data from a willingness to pay auction combined with decoding techniques to reveal...

SUMMARY Background Uncertainty shapes our perception of the world and the decisions we make. Two aspects of uncertainty are commonly distinguished: uncertainty in previously acquired knowledge (prior) and uncertainty in current sensory information (likelihood). Previous studies have established that humans can take both types of uncertainty into account, often in a way predicted by Bayesian statistics. However, the neural representations underlying these parameters remain poorly understood. Results By varying prior and likelihood uncertainty in a decision-making task while performing neuroimaging in humans, we found that prior and likelihood uncertainty had quite distinct representations. While likelihood uncertainty activated brain regions along the early stages of the visuomotor pathway, representations of prior uncertainty were identified in specialized brain areas outside this pathway, including putamen, amygdala, insula, and orbitofrontal cortex. Furthermore, the magnitude of brain activity in the putamen predicted individuals’ personal tendencies to rely more on either prior or current information. Conclusions Our results suggest different pathways by which prior and likelihood uncertainty map onto the human brain, and provide a potential neural correlate for higher reliance on current or prior knowledge. Overall, these findings offer insights into the neural pathways that may allow humans to make decisions close to the optimal defined by a Bayesian statistical framework.

It is widely assumed that the thalamus is functionally irrelevant for the sense of smell. Although animal studies suggest that the mediodorsal (MD) thalamus links primary olfactory (piriform) cortex to olfactory neocortical projection sites in orbitofrontal cortex (OFC), this transthalamic route is regarded to be inconsequential, particularly compared with a direct monosynaptic pathway linking piriform cortex and OFC. In this study, we combined functional magnetic resonance imaging with novel effective connectivity techniques to measure attention-dependent network coherence within direct (nonthalamic) and indirect (transthalamic) olfactory pathways. Human subjects were presented with (or without) an odor and with (or without) a tone, while selectively attending to either modality. Attention to odor significantly modulated neural coupling within the indirect pathway, strengthening MD thalamus-OFC connectivity. Critically, these effects were modality specific (odor Ͼ tone attention), directionally sensitive (forward Ͼ backward connections), and selective to route (indirect Ͼ direct pathway). Our findings support the idea that the human transthalamic pathway is an active modulatory target of olfactory attention. The results imply that olfaction, like all other sensory modalities, requires a thalamic relay, if only to consciously analyze a smell.

Highlights d How the human brain supports navigation in an odorous landscape is poorly understood d Subjects learn to orient within a 2D intensity space defined by two different odors d Odor navigation elicits grid-cell-like activity in prefrontal and entorhinal cortices d Findings suggest a mechanism by which the brain constructs olfactory cognitive maps