The Sleeping Infant Brain Anticipates Development Manuela Friedrich, Ines Wilhelm, Matthias Mölle, Jan Born, Angela D. Friederici  Current Biology  Volume 27, Issue 15, Pages 2374-2380.e3 (August 2017) DOI: 10.1016/j.cub.2017.06.070 Copyright © 2017 Elsevier Ltd Terms and Conditions

Current Biology 2017 27, 2374-2380.e3DOI: (10.1016/j.cub.2017.06.070) Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 1 Experimental Design (A) In the learning phase, half of the presented object-word pairs appeared in the consistent pairing condition, in which a word was paired once with each of eight novel, but similar, objects, allowing the learning of category-word pairings. The other half appeared in the inconsistent pairing condition, in which a word was repeated for the same number of times but paired once with each of eight dissimilar objects, such that stable pairings could not be learned. (B) In the memory test, each of the four novel objects of the categories were presented either as correct pairings with their labeling word of the learning phase or as incorrect pairings with a word previously taken to label another category. Current Biology 2017 27, 2374-2380.e3DOI: (10.1016/j.cub.2017.06.070) Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 2 Category-Word Pairing Effects during Learning and Memory Testing The infant ERPs in response to words paired with novel category exemplars. Following standard analyses of the N400 priming effect, we calculated all memory effects as the difference between unprimed and primed conditions (i.e., inconsistent − consistent and incorrect − correct); negativity is plotted upward. (A) No evidence for generalization during learning. (B) No evidence for generalization in the memory test of the wake group. (C) Late negativity (cluster involving CP5, T7, P7, P3, PZ, P4, C3, CZ, C4, and FC3) in the memory test of the short-nap group, indicating the presence of lower-developed perceptual-associative memory for the category-word pairings. (D) N400 cluster (involving PZ, CZ, P4, and C4) in the memory test of the long-nap group, indicating the presence of higher-developed lexical-semantic memory. Current Biology 2017 27, 2374-2380.e3DOI: (10.1016/j.cub.2017.06.070) Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 3 The Time Course of Memory Formation during Sleep Stage 2 (A) Late negative memory effect in the short-N2 group (infants with N2 duration below or equal to the median of 9.5 min). (B) N400 memory effect in the long-N2 group (infants with N2 duration above the median of 9.5 min). (C) No evidence for a memory effect in infants, who stayed in N2 for 0.5–4 min. (D) Late negativity (t18 = 2.629, p = 0.017) in infants, who stayed in N2 for 4.5–9.5 min, indicating the presence of perceptually based associative memory. (E) Missing memory effect in infants, who stayed in N2 for 10–17.5 min, suggesting that memory reorganization was in progress. (F) N400 effect (t16 = −2.356, p = 0.032) in infants, who stayed in N2 for 18–35 min, attesting the establishment of lexical-semantic memory. See also Table S3 and S4. Current Biology 2017 27, 2374-2380.e3DOI: (10.1016/j.cub.2017.06.070) Copyright © 2017 Elsevier Ltd Terms and Conditions

Figure 4 The Relation between Sleep Spindles and Lexical-Semantic Memory (A) EEG power during NREM sleep for frontal (mean of F3, FZ, and F4), central (mean of C3, CZ, and C4), and parietal (mean of P3, PZ, and P4) channels. (B) Averaged NREM sleep spindles for the short- and long-N2 groups. (C) Correlation between mean peak-to-peak amplitude of sleep spindles at the right central brain region (C4) during sleep stage 2 of the nap in the retention period and the N400 semantic generalization effect in the memory test of the long-N2 group (r = −0.488, p = 0.006). (D) Correlation between mean spindle RMS at C4 in N2 and the N400 memory effect of the long-N2 group (r = −0.526, p = 0.003). Note that due to the negative polarity of the N400 effect the correlations are also negative. See also Figure S1. Current Biology 2017 27, 2374-2380.e3DOI: (10.1016/j.cub.2017.06.070) Copyright © 2017 Elsevier Ltd Terms and Conditions