22. L. K. Medlin, A. G. Sáez, J. R. Young, Mar. Micropaleontol. 67, 69 (2008). 23. A. Sáez et al., in Coccolithophores: From Molecular Processes to Global Impact, H. R. Y. Thierstein, J. R. Young, Eds. (Springer, Berlin, 2004), pp. 251–269. 24. P. R. Bown, J. A. Lees, J. R. Young, Eds., Calcareous Nannoplankton Evolution and Diversity Through Time (Springer, Berlin and Heidelberg, 2004), pp. 481–508. 25. W. G. Siesser, T. J. Bralower, E. H. Carlo, Proc. Ocean Drill. Prog. Sci. Results 122, 653 (1992). 26. E. Paasche, Phycologia 40, 503 (2001). 27. Materials and methods are available as supplementary materials on Science Online. 28. N. Musat et al., Proc. Natl. Acad. Sci. U.S.A. 105, 17861 (2008). 29. F. J. R. Taylor, Ann. Inst. Oceanogr. 58, 61 (1982). 30. M. V. Zubkov, G. A. Tarran, Nature 455, 224 (2008). 31. F. Unrein, R. Massana, L. Alonso-Sáez, J. M. Gasol, Limnol. Oceanogr. 52, 456 (2007). 32. D. M. Karl, M. J. Church, J. E. Dore, R. M. Letelier, C. Mahaffey, Proc. Natl. Acad. Sci. U.S.A. 109, 1842 (2012). 33. S. C. Doney, V. J. Fabry, R. A. Feely, J. A. Kleypas, Annu. Rev. Mar. Sci. 1, 169 (2009). Acknowledgments: D. Bottjer and M. Hogan provided advice for 15 N 2 additions. Water samples were collected with the help of S. Curless, M. Church, S. Wilson, S. Tozzi, and the captain and crew of the research vessel Kilo Moana. On-board flow cytometry was made possible by K. Doggett and D. Karl. Funding was provided by the Gordon and Betty Moore Foundation ( J.P.Z.) and the NSF Center for Microbial Oceanography: Research and Education (C-MORE). The Max Planck Society sponsored the HISH-SIMS analysis. We thank G. Lavik (Max Planck Institute, Bremen) for advice and suggestions for data analysis. J. Waterbury provided the scientific name for UCYN-A. D.V. was supported by PHYTOMETAGENE ( JST-CNRS), METAPICO (Genoscope), and Micro B3 (funded by the European Union, contract 287589). BIOSOPE metagenome sequencing was performed at Genoscope (French National Sequencing Center) by J. Poulain. We thank H. Claustre, A. Sciandra, D. Marie, and all other BIOSOPE cruise participants. GenBank accession nos.: JX291679 to JX291804 and JX291547 to JX291678 (see table S4 for details). Supplementary Materials www.sciencemag.org/cgi/content/full/337/6101/1546/DC1 Materials and Methods Figs. S1 and S2 Tables S1 to S6 References (34–46) 2 April 2012; accepted 20 July 2012 10.1126/science.1222700 Disruption of Reconsolidation Erases a Fear Memory Trace in the Human Amygdala Thomas Agren, 1 Jonas Engman, 1 Andreas Frick, 1 Johannes Björkstrand, 1 Elna-Marie Larsson, 2 Tomas Furmark, 1 Mats Fredrikson 1 Memories become labile when recalled. In humans and rodents alike, reactivated fear memories can be attenuated by disrupting reconsolidation with extinction training. Using functional brain imaging, we found that, after a conditioned fear memory was formed, reactivation and reconsolidation left a memory trace in the basolateral amygdala that predicted subsequent fear expression and was tightly coupled to activity in the fear circuit of the brain. In contrast, reactivation followed by disrupted reconsolidation suppressed fear, abolished the memory trace, and attenuated fear-circuit connectivity. Thus, as previously demonstrated in rodents, fear memory suppression resulting from behavioral disruption of reconsolidation is amygdala-dependent also in humans, which supports an evolutionarily conserved memory-update mechanism. A nxiety disorders are common, and they cause great suffering and high societal costs (1). The etiology involves amygdala- dependent memory mechanisms that link stress- ful events to previously neutral stimuli (2), and the amygdala has been demonstrated to be hy- perresponsive across the anxiety disorders (3). Pharmacological and behavioral treatments of anxiety reduce symptomatology and amygdala activity (4) but have limited success because re- lapses occur (5). However, fear memories may be erased by recalling them and preventing their reconsolidation (6, 7). In rodents, the amygdala seems vital for fear memory reconsolidation (7, 8), but this has not been investigated in humans. Fear conditioning, in which a previously neu- tral stimulus turns into a conditioned stimulus (CS) through pairings with an aversive stimulus, forms a memory trace in the amygdala (2). Mem- ory activation produces behavioral (2, 9) and autonomic fear reactions, such as skin conduct- ance responses (SCRs) (10–12), frequently used to measure fear learning. Studies in animals (13) and anxiety patients (14) demonstrate that ex- tinction weakens, but does not erase, fear mem- ories. In rodents (13) and humans (15) alike, extinction attenuates conditioned fear expression through prefrontal inhibition. Fear can return af- ter stress, be renewed when altering the envi- ronmental context, or reoccur with the passage of time (16). By activating memories and disrupting their reconsolidation, through protein synthesis block- ade local in the amygdala (8) or through systemic administration of b-adrenergic receptor antago- nists (17, 18), fear memories are inhibited. Fear memory reconsolidation can also be disrupted behaviorally (6, 7, 19). In rodents, extinction of fear conditioning performed 10 or 60 min after presenting a reminder of the conditioned fear, but not after 6 or 24 hours, inhibited fear expression (7). Fear did not return in a new context, after shock exposure, or with time. Thus, extinction conducted within, but not outside, the reconsoli- dation window resulted in permanent attenuation of the fear memory (7). In humans, extinction performed within the reconsolidation interval also inhibited fear, whereas extinction training performed outside of the reconsolidation interval spared the mem- ory and fear returned (6). In animals, the neu- ral functions enabling fear memory formation and reconsolidation are located in the amyg- dala (2, 7–9, 20). In humans, lesion (21) and brain imaging studies (10–12, 22) confirm that the amygdala is a key area for fear memory en- coding. To test the hypothesis that reconsolida- tion in humans is amygdala-mediated and that disruption of reconsolidation inactivates a mem- ory trace in the basolateral amygdala, we per- formed a study combining brain imaging with a physiological measure of fear. On day 1, twenty-two subjects (11 women) aged 24.0 T 0.48 (mean T SEM) underwent fear conditioning to establish an associative fear memory (Fig. 1A and fig. S1). On day 2, the fear memory was reactivated by presenting the cue previously paired with the shock (CS+) for 2 min. Subjects were randomized into two groups. One group received extinction, consisting of repeated CS presentations with the shock withheld, 10 min after reactivation and thus within the reconsol- idation interval. The other group received extinc- tion 6 hours after the reactivation—i.e., outside of the interval. Fear expression was measured using SCRs (6, 19). On day 3, a renewal session was performed in a new environment, a magnetic res- onance scanner, where shock electrodes were at- tached, although no shocks were delivered. SCRs were not measured for technical reasons. On day 5, subjects were exposed to unsignaled shocks and then re-exposed to CS+. Return of fear was defined as the increase in SCR from the last ex- tinction trial on day 2 to the first reinstatement trial on day 5 (Fig. 1B) (6). First, we evaluated if the predicted behavioral reinstatement effect was present on day 5. Con- firming this, increased fear responding was ob- served in the 6 hours, but not the 10 min group 1 Department of Psychology, Uppsala University, SE-751 42 Uppsala, Sweden. 2 Department of Radiology, Oncology and Radiation Science, Uppsala University, SE-751 42 Uppsala, Sweden. *To whom correspondence should be addressed. E-mail: thomas.agren@psyk.uu.se 21 SEPTEMBER 2012 VOL 337 SCIENCE www.sciencemag.org 1550 REPORTS