Stress Sensitizes the Brain: Increased Processing of Unpleasant Pictures after Exposure to Acute Stress Mathias Weymar 1,2 , Lars Schwabe 3 , Andreas Löw 1 , and Alfons O. Hamm 1 Abstract ■ A key component of acute stress is a surge in vigilance that enables a prioritized processing of highly salient information to promote the organismʼs survival. In this study, we investigated the neural effects of acute stress on emotional picture process- ing. ERPs were measured during a deep encoding task, in which 40 male participants categorized 50 unpleasant and 50 neutral pictures according to arousal and valence. Before picture encod- ing, participants were subjected either to the Socially Evaluated Cold Pressor Test (SECPT) or to a warm water control procedure. The exposure to the SECPT resulted in increased subjective and autonomic (heart rate and blood pressure) stress responses rela- tive to the control condition. Viewing of unpleasant relative to neutral pictures evoked enhanced late positive potentials (LPPs) over centro-parietal scalp sites around 400 msec after picture onset. Prior exposure to acute stress selectively increased the LPPs for unpleasant pictures. Moreover, the LPP magnitude for unpleasant pictures following the SECPT was positively associated with incidental free recall performance 24 hr later. The present results suggest that acute stress sensitizes the brain for increased processing of cues in the environment, particularly priming the processing of unpleasant cues. This increased processing is re- lated to later long-term memory performance. ■ INTRODUCTION Acute stressful events not only initiate a stress response in the body but also influence various types of cognitive functions, such as vigilance, attention, and memory. These responses in both the body and the brain are mediated by neurotransmitters, peptides, and hormones, such as cate- cholamines and glucocorticoids, affecting several brain areas, including the amygdala, the hippocampus, and the PFC ( Joëls & Baram, 2009; Roozendaal, McEwen, & Chattarji, 2009). Recent functional imaging findings indicate that acute stress is associated with increased activation of the amygdala and primary visual areas during processing of emotional stimuli, compared with the nonstress condition, suggesting that processing of significant stimuli in the environment is facilitated after acute stress (van Marle, Hermans, Qin, & Fernández, 2009; see also Henckens, Hermans, Pu, Joëls, & Fernández, 2009). Furthermore, increased coactivations between the amygdala and attentional networks (e.g., dorsal ACC and anterior insula) are observed in a resting state without experimental task after continuously watching highly stressful (vs. emotionally neutral) film clips (van Marle, Hermans, Qin, & Fernández, 2010). These results suggest that acute stress sensitizes the organism for prioritized sensory processing of (threat-related) potentially significant information. Furthermore, several studies suggest that acute stress also facilitates memory consolidation. Acute stress admin- istered before or shortly after encoding of emotional pic- tures (Cahill, Gorski, & Le, 2003; Buchanan & Lovallo, 2001) results in enhanced long-term memory for these emo- tional events, indicating also a substantial role of emotional arousal on stress-mediated memory formation (Schwabe, Bohringer, Chatterjee, & Schachinger, 2008; Payne et al., 2007; Cahill et al., 2003; Buchanan & Lovallo, 2001; for re- views, see Schwabe, Wolf, & Oitzl, 2010; McGaugh, 2004). On the basis of these findings, acute stress seems to sen- sitize the facilitated processing of emotional stimuli and may also promote memory consolidation. Previous ERP studies indicate that the processing of high- arousing emotional (pleasant and unpleasant) compared with low-arousing neutral stimuli evokes increased late po- sitive potentials (LPPs) starting about 400 msec poststimulus over centro-parietal regions (Ferrari, Bradley, Codispoti, & Lang, 2011; Hajcak & Olvet, 2008; Codispoti, Ferrari, & Bradley, 2007; Schupp, Junghöfer, Weike, & Hamm, 2004; Cuthbert, Schupp, Bradley, Birbaumer, & Lang, 2000; for a review, see Lang & Bradley, 2010). The LPP is particularly enhanced for pictures rated highest in emotional arousal and contents with high evolutionary significance (e.g., erotica and mutilated bodies; Schupp, Cuthbert, et al., 2004). A similar enlarged centro-parietal positive potential is observed during processing of target compared with 1 University of Greifswald, 2 University of Florida, 3 Ruhr-University Bochum © 2012 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 24:7, pp. 1511–1518