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 24 publications 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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  • How tumor cells hijack healthy cells to promote metastasis   (2017)

    Trepat, Xavier (IBEC)

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    Metastasis, responsible for the majority of deaths in patients with cancer, is the process by which cancer cells separate from the original tumor to form new tumors in other organs or tissues of the body. Although initially some types of carcinoma have a very limited ability to invade the tissue around them, they finally find the mechanism to do so, thus increasing the aggressiveness of the cancer.

    In this study, we identified a mechanism by which cancer cells manage to escape the tumor to promote metastasis. The study revealed that tumor cells can reprogramme their healthy neighbours, dragging them out of the tumor and into other tissues. The victims of this ‘kidnapping’ are fibroblasts, a cell type that is responsible for the synthesis and organization of the extracellular matrix. Fibroblasts are "professionals" in maintaining healthy tissues, and are able to create tunnels in the tissues to travel through. They use this ability to restore the tissues when we suffer an injury.

    We discovered that cancer cells use the mobility of fibroblasts to escape the tumor and travel through tissues. The surrounding tumor, or stroma, modifies these fibroblasts and uses them for the invasion. From this point, the fibroblasts turn ‘bad’ and start to serve the cancerous cells, tracing paths for them through the extracellular matrix surrounding the tumor.

    The main challenge of the study was to identify the mechanism by which cancer cells adhere to fibroblasts and move together. This turned out to be a a biophysical interaction between two different proteins, one located on the surface of cancer cells called E-cadherin, and another expressed on the surface of fibroblasts, called N-cadherin. Despite the different natures of the two proteins, the study reveals that the join between cancer cells and fibroblasts is just as strong as that which connects cancer cells, which emphasizes that this unusual interaction is much more effective than previously thought.


  • An agrowth strategy to deal with limits-to-growth as a barrier to climate policy (2017)

    van den Bergh, Jeroen (UAB)

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    The fear that stringent climate policy will hamper future economic growth is an important reason for many voters and politicians to be hesitant about giving their support to it. It partly explains why the 2009 Copenhagen climate summit largely failed and the recent Paris Agreement was designed around voluntary climate targets instead of effective policies. As the window to curb warming at 2°C closes, the debate on growth-versus-climate is likely to intensify. A critical review of theoretical and empirical findings indicates that the two polar positions, ‘green growth’ and ‘anti-growth’, are both risky and not guaranteed to combine climate and social goals.

    This does not mean that green growth is impossible. The economy has a tremendous flexibility to change. It just needs to be triggered by effective climate policies. A precautionary strat­egy would, though, involve preparing society for the scenario that green policies do not go along with growth. Some have responded with a radical proposal for 'degrowth'. Aside from being politically unrealistic, it confuses cause and effect: perhaps climate policy will result in negative growth, but this does not imply a reverse causality, that a negative growth strategy effectively solves climate change.

    A third option has been over­looked: a ‘growth-agnostic’ or ‘agrowth’ strategy. Its motivation is the insight that GDP (gross domestic product) is not a good proxy of social welfare. Hence, this strategy is to ignore time changes in GDP. This allows for unconstrained search in the largest area in the accompanying Figure 1, namely a + b1+ b2, meaning maximum flexibil­ity to reach a high level of social welfare, and avoid ending up in undesir­able areas c1, c2 or d. An agrowth strategy does not beforehand exclude any option: negative growth (area a), zero-growth (line h), low growth (b1) or high growth (b2). It just aims to achieve acceptable values of factors con­tributing to human well-being (O), including employment, equity and a safe climate.

    An agrowth strategy can depolarize the growth-versus-climate debate and reduce resistance to effective climate policy. It is elaborated in six concrete strategies.

  • Stop-Motion Shoots of a Single Molecule (2017)

    van Hulst, Niek F. (ICFO)

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    For over two centuries optical spectroscopy is revealing the nature, interactions and reactions of atoms, molecules, proteins, etc. Since 25 years, one can even see individual molecules, providing ultimate details of biological and chemical systems, enabling super-resolution microscopy, single particle tracking, detection of rare states, etc. Even dynamic processes, such as molecular conformational changes and energy transfer are becoming accessible at the level of the individual molecule. Yet, these processes are fast, very fast, occurring on femtosecond to picosecond timescale. The challenge of a spectral snapshot on femtosecond scale has so far prevented to track any spectral development of a single molecule at true molecular timescale.

    At ICFO, we have finally resolved this dilemma by performing time-resolved ultrafast encoded single molecule spectroscopy (“True”SMS). Tracing the femtosecond evolution of excited electronic state spectra of single molecules over hundreds of nanometres of bandwidth at room temperature, we managed to reveal the nonlinear ultrafast response in an effective three-pulse scheme with depleted fluorescence detection. A first excitation pulse was followed by a phase-locked de-excitation pulse pair, providing spectral encoding with 25 fs temporal resolution. Just as in a stop-motion movie, yet millions-times-millions times faster, the molecular spectral development is shot. Probing the spectral evolution of the stimulated emission transition, initially (<100fs) the electronic band developed, while in the long time-delay (>1ps) spectrum the two-band feature reminiscent of a vibrational progression emerged, confirming the dynamic vibronic transition of the single molecule.

    This first experimental realization of true single-molecule transient spectroscopy demonstrates that two-dimensional electronic spectroscopy of single molecules is experimentally within reach, opening routes to study energy transfer and charge transfer of photosynthetic complexes, perovskites and photovoltaic systems at the ultimate level of a single unit.


  • How perception shapes our actions (2017)

    Verschure, Paul FMJ (IBEC)

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    The dominant view in neuroscience interprets the ability of the brain to produce anticipatory actions as a sensory-motor process driven by errors in motor performance: an error in behavior triggers corrective motor commands that are executed before the less optimal action is realized. Verschure and colleagues challenge this dominant account of anticipatory motor control and advance a novel answer to this question based on a theoretical model. This alternative model is necessary because the traditional models based on the direct acquisition or motor commands do not sufficiently account for the dependence of action on intentions of the agent and context. Actions driven by sensory predictions are indeed more robust to the uncertainty of the environment and they can be generalized to different body configurations without being retrained.

    According to Maffei et al. (2017) animals seamlessly and unconsciously control their body based on an internal simulation of what the world will be like just after motor actions are realized. Lower level motor systems that are specialized in fast movement generation, react as if this brain generated simulation is actual. Through learning, this internal simulation will get more and more precise in predicting the future and the motor systems that respond to it better tuned to how the body interacts with the real world. In other words, our ability to generate anticipatory actions stem from the ability of the brain to internally predict the future and process those predictions as relevant information attend and react to. Adaptive fast and skilled motor action thus result from the surprising ability of the brain to simulate the future. The idea of the brain as a predictive system as such is not new and indeed the brain theories that Verschure and Friston have independently proposed. The model advanced by Maffei et al realizes this unification of the Free Energy framework of Karl Friston and the Distributed Adaptive Control theory of Verschure by integrating results from neuroanatomy and physiology, experimental psychology, robotics, and control engineering. 

  • "Universal" Laws of Thermodynamics (2017)

    Winter, Andreas (ICFO)
    Lewenstein, Maciej Andrzej (ICFO)

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    Thermodynamics is one of the most successful physical theories ever formulated. Though it was initially
    developed to deal with steam engines and, in particular, the problem of conversion of heat into mechanical
    work, it has prevailed even after the scientific revolutions of relativity and quantum mechanics. Despite its wide
    range of applicability, it is known that the laws of thermodynamics break down when systems are correlated
    with their environments. In the presence of correlations, anomalous heat flows from cold to hot baths become
    possible, as well as memory erasure accompanied by work extraction instead of heat dissipation.
    Here, we generalize thermodynamics to physical scenarios which allow the presence of correlations, including
    those where strong correlations are present. We exploit the connection between information and physics, and
    introduce a consistent redefinition of heat dissipation by systematically accounting for the information flow
    from system to bath in terms of the conditional entropy. As a consequence, the formula for the Helmholtz free
    energy is accordingly modified. Such a remedy not only fixes the apparent violations of Landauer’s erasure
    principle and the second law due to anomalous heat flows, but it also leads to a reformulation of the laws of
    thermodynamics that are universally respected. In this information-theoretic approach, correlations between
    system and environment store work potential. Thus, in this view, the apparent anomalous heat flows are the
    refrigeration processes driven by such potentials.

  • 400,000 year-old fossil cranium from Gruta da Aroeira, Almonda karst system (Portugal) (2017)

    Zilhão, João (UB)

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    The fossil  is the westernmost Middle Pleistocene cranium of Europe and is one of the earliest fossils from this region associated with Acheulean tools. Unlike most other Middle Pleistocene finds, which are of uncertain chronology, the Aroeira 3 cranium is firmly dated to around 400 ka and was in direct association with abundant faunal remains and stone tools. In addition, the presence of burnt bones suggests a
    controlled use of fire. The Aroeira cranium represents a substantial contribution to the debate on the origin of the Neandertals and the pattern of human evolution in the Middle Pleistocene of Europe.