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<jats:title>An intrinsic magnetic tunnel junction</jats:title> <jats:p> An electrical current running through two stacked magnetic layers is larger if their magnetizations point in the same direction than if they point in opposite directions. These so-called magnetic tunnel junctions, used in electronics, must be carefully engineered. Two groups now show that high magnetoresistance intrinsically occurs in samples of the layered material CrI <jats:sub>3</jats:sub> sandwiched between graphite contacts. By varying the number of layers in the samples, Klein <jats:italic>et al.</jats:italic> and Song <jats:italic>et al.</jats:italic> found that the electrical current running perpendicular to the layers was largest in high magnetic fields and smallest near zero field. This observation is consistent with adjacent layers naturally having opposite magnetizations, which align parallel to each other in high magnetic fields. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1218" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar3617">1218</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1214" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar4851">1214</jats:related-article> </jats:p>

<jats:title>An intrinsic magnetic tunnel junction</jats:title> <jats:p> An electrical current running through two stacked magnetic layers is larger if their magnetizations point in the same direction than if they point in opposite directions. These so-called magnetic tunnel junctions, used in electronics, must be carefully engineered. Two groups now show that high magnetoresistance intrinsically occurs in samples of the layered material CrI <jats:sub>3</jats:sub> sandwiched between graphite contacts. By varying the number of layers in the samples, Klein <jats:italic>et al.</jats:italic> and Song <jats:italic>et al.</jats:italic> found that the electrical current running perpendicular to the layers was largest in high magnetic fields and smallest near zero field. This observation is consistent with adjacent layers naturally having opposite magnetizations, which align parallel to each other in high magnetic fields. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1218" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar3617">1218</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1214" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar4851">1214</jats:related-article> </jats:p>

<jats:title>Shifts in brain regions with brain size</jats:title> <jats:p> Brain size among normal humans varies as much as twofold. Reardon <jats:italic>et al.</jats:italic> surveyed the cortical and subcortical structure of more than 3000 human brains by noninvasive imaging (see the Perspective by Van Essen). They found that the scaling of different regions across the range of brain sizes is not consistent: Some brain regions are metabolically costly and are favored in larger brains. This shifts the balance between associative and sensorimotor brain systems in a brain size–dependent way. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1222" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar2578">1222</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1184" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aat8948">1184</jats:related-article> </jats:p>

<jats:title>Disentangling specific memories</jats:title> <jats:p> Each memory is stored in a distinct memory trace in the brain, in a specific population of neurons called engram cells. How does the brain store and define the identity of a specific memory when two memories interact and are encoded in a shared engram? Abdou <jats:italic>et al.</jats:italic> used optogenetic reactivation coupled with manipulations of long-term potentiation to analyze engrams that share neurons in the lateral amygdala (see the Perspective by Ramirez). Synapse-specific plasticity guaranteed the storage and the identity of individual memories in a shared engram. Moreover, synaptic plasticity between specific engram assemblies was necessary and sufficient for memory engram formation. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1227" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aat3810">1227</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1182" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aau0043">1182</jats:related-article> </jats:p>

<jats:title>Nocturnal refuge</jats:title> <jats:p> As the human population grows, there are fewer places for animals to live out their lives independently of our influence. Given our mostly diurnal tendencies, one domain that remains less affected by humans is the night. Gaynor <jats:italic>et al.</jats:italic> found that across the globe and across mammalian species—from deer to coyotes and from tigers to wild boar—animals are becoming more nocturnal (see the Perspective by Benítez-López). Human activities of all kinds, including nonlethal pastimes such as hiking, seem to drive animals to make use of hours when we are not around. Such changes may provide some relief, but they may also have ecosystem-level consequences. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1232" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aar7121">1232</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1185" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aau1311">1185</jats:related-article> </jats:p>

<jats:title>How to make bioactive alkaloids</jats:title> <jats:p> Vinblastine and vincristine are important, expensive anticancer agents that are produced by dimerization of the plant-derived alkaloids catharanthine and vindoline. The enzymes that transform tabersonine into vindoline are known; however, the mechanism by which the scaffolds of catharanthine and tabersonine are generated has been a mystery. Caputi <jats:italic>et al.</jats:italic> now describe the biosynthetic genes and corresponding enzymes responsible. This resolves a long-standing question of how plant alkaloid scaffolds are synthesized, which is important not only for vinblastine and vincristine biosynthesis, but also for understanding the many other biologically active alkaloids found throughout nature. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1235" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aat4100">1235</jats:related-article> </jats:p>

<jats:title>The mechanisms of fear attenuation</jats:title> <jats:p> Surprisingly little is known about how remote fearful memories are stored and attenuated. Khalaf <jats:italic>et al.</jats:italic> used independent fear memory attenuation paradigms, engram-based tagging techniques, and chemogenetic tools to alter neuronal activity (see the Perspective by Frankland and Josselyn). They found that a discrete subset of neurons within an ensemble is engaged during recall after memory attenuation, which correlated with fear reduction. Memory updating and extinction mechanisms thus likely coexist to make this happen. These findings support the notion that effective memory attenuation is mediated by a rewriting of the original memory trace of fear toward one of safety. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1239" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aas9875">1239</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1186" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aau0035">1186</jats:related-article> </jats:p>

<jats:title>Tackling microtubule-tau interactions</jats:title> <jats:p> Alzheimer's disease is a major cause of death in the elderly. Disease progression is associated with the accumulation of neurofibrillary tangles composed of tau, a protein important for neuronal development and function. Tangle formation is preceded by phosphorylation events that cause tau to dissociate from its native binding partner, microtubules. Microtubule-tau interactions have been mysterious. Kellogg <jats:italic>et al.</jats:italic> used cryo–electron microscopy and molecular modeling to show how tau interacts with the outer surface of the microtubule, stapling together tubulin subunits and thus stabilizing the polymer. A key tau amino acid within the tightly bound segment between tubulin subunits corresponds to a clinically relevant site of tau phosphorylation, explaining the competition between microtubule interaction and tau aggregation. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1242" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aat1780">1242</jats:related-article> </jats:p>

<jats:title>Seeing ghosts</jats:title> <jats:p> In fluorescence-activated cell sorting, characteristic target features are labeled with a specific fluorophore, and cells displaying different fluorophores are sorted. Ota <jats:italic>et al.</jats:italic> describe a technique called ghost cytometry that allows cell sorting based on the morphology of the cytoplasm, labeled with a single-color fluorophore. The motion of cells relative to a patterned optical structure provides spatial information that is compressed into temporal signals, which are sequentially measured by a single-pixel detector. Images can be reconstructed from this spatial and temporal information, but this is computationally costly. Instead, using machine learning, cells are classified directly from the compressed signals, without reconstructing an image. The method was able to separate morphologically similar cell types in an ultrahigh-speed fluorescence imaging–activated cell sorter. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6394" page="1246" related-article-type="in-this-issue" vol="360" xlink:href="10.1126/science.aan0096">1246</jats:related-article> </jats:p>

<jats:p>A weekly roundup of information on newly offered instrumentation, apparatus, and laboratory materials of potential interest to researchers.</jats:p>