Every year, a committee of experts sits down with a tough job to do: from among all ICREA publications, they must find a handful that stand out from all the others. This is indeed a challenge. The debates are sometimes heated and always difficult but, in the end, a shortlist of  the most outstanding publications of the year is produced. No prize is awarded, and the only additional acknowledge is the honour of being chosen and highlighted by ICREA. Each piece has something unique about it, whether it be a particularly elegant solution, the huge impact it has in the media or the sheer fascination it generates as a truly new idea. For whatever the reason, these are the best of the best and, as such, we are proud to share them here.


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  • The identification of human Colon Stem Cells and Colon Cancer Stem Cells (2011)

    Batlle Gómez, Eduard (IRB Barcelona)

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    The identification of human Colon Stem Cells and Colon Cancer Stem Cells

    The inner layer of the intestinal tube, the intestinal epithelium, is in a constant process of renewal. Hundreds of millions of terminally differentiated intestinal cells are replaced by new cells every day during the life of an adult organism. This tremendous regenerative power is ultimately sustained by a small population of intestinal stem cells. It is believed that alterations in the biology of human colon stem cells (CoSCs) account for the pathophysiology of various large-bowel disorders, including colorectal cancer (CRC). Yet, the identification of human CoSCs had remained elusive. In these manuscripts we describe for the first time the isolation of stem cells of the human colonic epithelium. Differential cell surface abundance of the receptor EPHB2 allows the purification of different cell types from human normal colon mucosa biopsies. Colon epithelial cells with highest EPHB2 levels exhibit the longest telomeres and express markers characteristic of intestinal stem cells. Using culturing conditions that recreate the intestinal stem cell niche, a substantial proportion of EPHB2-high cells can be expanded in vitro as an undifferentiated and multipotent population. This discovery has profound implications for the field of regenerative medicine as it opens the possibility of using CoSCs as a therapeutic tool. In parallel, my group applied the same method of stem cell purification to human CRCs. These experiments led us to demonstrate that most human CRCs are constituted by cell populations with phenotypes similar to either CoSCs or intestinal differentiated cells organized into well-defined compartments. CoSC-like cells purified from primary CRCs generate tumors in immunodeficient mice with high efficiency and display both self-renewal and differentiation capacity. Remarkably, the expression of the CoSC gene program predicts disease relapse after intended curative therapy in CRC patients. Overall, these results imply that CRC shares a common hierarchy with the intestinal mucosa and that the acquisition of an intestinal stem cell gene program is a central process in the development of metastatic and recurrent CRC.

  • At the origins of human rationality: how infants reason about future unknown events. (2011)

    Bonatti, Luca (UPF)

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    At the origins of human rationality: how infants reason about future unknown events.

    Humans excel at reasoning about novel situations, flexibly combining abstract knowledge and perceptual information from disparate sources in "one-shot" intuitions to predict outcomes of events they have never before directly experienced. To investigate the root of this ability, we study how infants reason in very simple, but completely novel situations which contain potentially conflicting information. Consider a simple situation in which three yellow objects and one blue object bounce inside a container with an opening on its lower side, as in a lottery machine (Figure 1). At a certain point, an occluder hides the container. You have to bet which object will exit first: will it be blue or yellow? The right answer is: it depends.
    The scene contains different kinds of information: about the properties of the objects, such as their colors; about the number of objects in the scene; or about the dynamics of their trajectories, collisions and changes in speed. All such potentially conflicting cues can be relevant to form optimal expectations about which object will exit the container. What is crucial is that the most relevant information can change according to subtle changes in how the scene unfolds.

    We showed prelinguistic infants such lottery-like scenes, by systematically varying the length of the occlusion prior to the exit of the object. When the occlusion was long, infants were surprised when an object of the less numerous category exited the container, irrespectively of its distance from the exit before the occlusion. This makes sense, because if the occlusion is long, the last position of an object is not relevant to predict what object will exit, as objects keep moving behind the occluder. Instead, when they saw the same situation but the occlusion was very short, infants were surprised when a far object exited, regardless of its color. Also this makes sense, because if an object is far from the exit, it becomes physically impossible for it to travel the distance to the exit during the short occlusion. Thus, infants have rational "gut feelings" about future events.
    In our study, we also elaborated a Bayesian ideal observer model which precisely predicts infants' looking times in our experiments and extends to other known results about infant cognition, providing for the first time a unifying explanation of several classic findings. This model shows how powerful pure reasoning capacities could derive from the operation of probabilistic inference mechanisms constrained by abstract principles of how

  • Entangled Photon Stored in Solid (2011)

    de Riedmatten, Hugues (ICFO)

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    Entangled Photon Stored in Solid

    Entanglement is one of the essential characteristics of quantum physics. It leads to very strong correlations between quantum particles that cannot be explained using classical physics. Beyond its fundamental significance, entanglement is also a crucial resource for quantum information science. For example, the strong correlations can be used to perform quantum key distribution, or to distribute an unknown quantum state via quantum state teleportation. As a result, a strong experimental effort is currently devoted worldwide to harnessing entanglement between various physical systems. In this context, entanglement between light and material systems is particularly interesting because it enables a connection between light based flying quantum bits that can be used to communicate over long distances, and matter based stationary quantum bits that can be used to store and process quantum information.
    In this paper, we demonstrate for the first time an entanglement experiment between a photon and a macroscopic, cm long crystal. This is realized by mapping one photon of an entangled pair onto a collective atomic excitation stored in the crystal and shared over ~ 1 billion Neodymium ions. The crystal is cooled down to 3 K in a cryostat in order minimize interactions between the Neodymium atoms and the crystal phonons that would destroy quantum coherence. The successful mapping of entanglement is proved by the violation of a Bell inequality.
    These results represent an important step towards quantum information technologies based on solid-state devices, in particular for quantum repeaters and long-distance quantum information networks. The experimental work has been performed at the University of Geneva. The research has been published in Nature, and highlighted in a News&Views article by Dr Jevon Longdell [2].

  • Emerging concepts for the dynamical organization of resting-state activity in the brain (2011)

    Deco, Gustavo (UPF)

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    Emerging concepts for the dynamical organization of resting-state activity in the brain

    A broad body of experimental work has demonstrated that apparently spontaneous brain activity is not random. At the level of large-scale neural systems, as measured with functional MRI (fMRI), this ongoing activity reflects the organization of a series of highly coherent functional networks. These so-called resting-state networks (RSNs) closely relate to the underlying anatomical connectivity but cannot be understood in those terms alone. Here we review three large-scale neural system models of primate neocortex that emphasize the key contributions of local dynamics, signal transmission delays and noise to the emerging RSNs. We propose that the formation and dissolution of resting-state patterns reflects the exploration of possible functional network configurations around a stable anatomical skeleton.

  • Better Colleagues, Better Work? (2011)

    Eeckhout, Jan (UPF)

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    Better Colleagues, Better Work?

    More able and skilled workers are more productive: by any measurable standard, they produce more and they earn higher wages. But are the same workers also more productive if the are surrounded by other more able and skilled co-workers? Casual observation of how much effort and resources are spent to put together the most appropriate teams of professionals seems to indicate the exact composition of collaborators matters a great deal. The most reputable hospitals vie for the best doctors, the best law firms make the best lawyers partner and top universities attract the best researchers. Yet, economist have found no evidence of such complementary effects economy-wide. Using social security data, wages are decomposed in a component due to the individual worker and one due to the characteristics of the firm environment. It turns out there is no significant correlation between these two components, and hence there is no evidence of those complementary effects.

    Jan Eeckhout (UPF) and Philipp Kircher (LSE) show that the lack of evidence is due to a flaw in the method. The main insight is that while working in a better firm does make all workers more productive, it does not necessarily increase wages. In fact, wages could be lower when getting a job in a better firm even if that worker is producing more output. This is due to mismatch, the fact that the better firm ideally would like to fill that position with a more skilled worker. For the firm to be willing to offer the job to one of lower ability, they will offer a lower wage. It is precisely this wage decrease that leads to failure to find evidence of the complementarities. They propose a method that takes this into account and permits for the correct inference from the data. Correctly measuring how strong those complementarities are is important to evaluate the losses from badly allocated teams of collaborators. And it is a key piece of information for policies that aim to achieve the optimal allocation of resources, for example unemployment insurance that provides incentives for the unemployed to look hard for the right job.

  • The art of magnetic writing (2011)

    Gambardella, Pietro (ICN2)

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    The art of magnetic writing

    Computer files that allow us to watch videos, store pictures, and edit all kinds of media formats are nothing else but streams of "0" and "1" digital data, that is, bits and bytes. Modern computing technology is based on our ability to write, store, and retrieve digital information as efficiently as possible. In a computer hard disk, this is achieved in practice by writing information on a thin magnetic layer, where magnetic domains pointing "up" represent a "1" and magnetic domains pointing down represent a "0".

    The size of these magnetic domains has now reached a few tens of nanometers, allowing us to store a Terabyte of data in the space of just a few square centimeters. Miniaturization, however, has created numerous problems that physicists and engineers worldwide struggle to solve at the pace demanded by an ever-growing information technology industry. The process of writing information on tiny magnetic bits one by one, as fast as possible, and with little energy consumption, represents one of the biggest hurdles in this field.

    A team of scientists from the Catalan Institute of Nanotechnology, in collaboration with SPINTEC researchers in France, has discovered a new method to write magnetic data that meets all of these requirements. Magnetic writing is currently performed using magnetic fields produced by wires and coils, a methodology suffering severe limitations in scalability and energy efficiency. The new technique eliminates this and provides extremely simple and reversible writing of memory elements by injecting an electric current parallel to the magnetic layer. The key to this effect lies in engineering a magnetic cobalt film less than one nanometer thick sandwiched between platinum and aluminum oxide. The research team showed that using current pulses that last less than 10 ns produced magnetic switching reliably at room temperature, while further miniaturization and faster switching appear easily within reach.

    This work has interesting applications for the magnetic recording industry, in particular the development of magnetic random access memories (MRAMs). By replacing standard RAMs, which need to be refreshed every few milliseconds, non-volatile MRAMs would allow instant power up of a computer and also save a substantial amount of energy. An additional advantage of the technique is that it is more efficient in "hard" magnetic layers that can be more easily miniaturized to nanometer dimensions, resulting in significantly increased information storage density. Three patent applications de