Adult-like N400m brain responses of 1-year-old infants. (A) Task used to demonstrate responses selective for words as compared with matched auditory controls. (B) Task used to demonstrate semantic priming by comparing the response with words preceded by congruous versus incongruous pictures. (C) Averaged single channel event-related fields from a representative 14-month infant. (C1) Word-selective activity (words > matched noise) peaks in left temporal channels at ∼440 ms. The average field strength in the 200 ms time window (350–550 ms) surrounding this peak in the displayed channels was measured on each trial (n = 106) and compared between congruous and incongruous conditions using a t-test (t₁₀₅ = 3.25, P < 0.002 [blue channel]; t₁₀₅ = 2.05, P < 0.04 [purple channel]). (C2) Semantic priming of brain activity in the same subject and sensors. Like the difference between words and noise (incongruous > congruous), the semantic effects were significant when compared across trials (n = 82) in the different conditions during the 200-ms period surrounding peak activity (t₈₁ = 2.13, P < 0.04 [blue channel]; t₈₁ = 2.88, P < 0.005 [purple channel]). (D) Whole-head MEG sensor array of the response selective for words as compared with noise, with color coding to indicate the left temporal gradiometers where the largest differential responses to word selective and semantic priming are observed for the individual subject shown in (C). (E) Group average dSPM activity (n = 4) to words and noise 200–400 ms following word onset. Words exhibit greater activity in left frontotemporal regions than noise. Color indicates signal-to-noise relative to prestimulus baseline (full red at sqrtF = 4.3, full yellow at sqrtF = 6.3). Subject number (S7) corresponds to subject 7 listed in Supplementary Table 2.

Cortical leadfields for left temporal gradiometers with the largest semantic priming response from an 18-month infant. (A) The cortical sensitivity of a given sensor is displayed on the pial surface. (A1–3) Channels are strongly sensitive to left posterior temporal regions and weakly to other perisylvian regions. Dipoles projecting 90% as strongly as strongest dipole are yellow; red dipoles project 50%, gray project <10%. (B) Significant semantically modulated activity (incongruous [red] > congruous [blue]) occurs between 350 and 550 ms. (C) The entire gradiometer array, showing that these channels have the largest differential responses to semantic priming of words. Color coding is consistent across all figures. Subject number (S11) corresponds to subject listed in Supplementary Table 2.

MEG recordings from adults during the semantic priming task developed for infants. (A) Averaged single channel event-related fields from a representative adult during the semantic priming task shown in . A sustained differential response (incongruous > congruous) is observed at a similar latency (350–550 ms) as infants, but the peak of the differential response may occur earlier for adults. This differential response is significant across trials for the 200-ms time window (350–550 ms) (P < 0.00001 [purple channel]; with a trend in the [blue channel] P < 0.08). Two-way t-test, P < 0.05, degrees of freedom = 98. (B) Whole-head MEG sensor array recordings of the semantic priming response in the same adult. Color coding indicates the left temporal gradiometer channels that correspond to where differential word selective, semantic, and repetition priming responses were observed in infants (, Supplementary Fig. S2). (C) Center: Adult average dSPM (n = 7) to incongruous minus congruous words at the same latency (500–550 ms) as the infant group response () displayed on the cortical surface (dark gray = sulci, light gray = gyri). Similar to infants, sources generating the differential semantic priming response are estimated in adults to left posterior prefrontal, perisylvian, and anterolateral temporal regions, with weaker activation in homologous right hemisphere sites. Color indicates signal-to-noise relative to prestimulus baseline (full red at sqrtF = 1.7 corresponding to P < 10⁻², full yellow at sqrtF = 3.5, P < 10⁻¹²). Surround: Average time courses for the estimated noise-normalized dipole strength to incongruous (red) and congruous (blue) words in the same 6 bilateral ROIs used for infant analyses. The amplitude of the time course to congruent and incongruent words from 500 to 550 ms was determined in each adult subject and compared with a paired t-test. Time courses with a * indicate regions where a significant difference was found (# = trend). IFS, inferior frontal sulcus; STS, superior temporal sulcus; ITS, inferior temporal sulcus.

Estimated localization of N400m activity modulated by semantic priming in 12- to 18-month-old infants. Center: Group average dSPM (n = 12) to incongruous minus congruous words from 500 to 550 ms (centered on the largest peak in the group time course activity), displayed on the cortical surface (dark gray = sulci, light gray = gyri). In the left hemisphere, activity is estimated to anterior and ventral temporal regions, insula, planum temporal, frontal operculum, inferior frontal sulcus, and orbital cortex. Right hemisphere activity is more restricted. Color indicates signal-to-noise relative to prestimulus baseline (full red sqrtF = 1.2, P < 0.05, full yellow sqrtF = 2.6, P < 10⁻⁷, degrees of freedom = 36). Surround: Average time courses for the estimated noise-normalized dipole strength to incongruous (red) and congruous (blue) words in 6 bilateral ROIs. The amplitude of the time course to congruent and incongruent words from 500 to 550 ms was determined in each subject and compared with a paired t-test. Time courses with a * indicate regions where a significant difference was found (# = trend). IFS, inferior frontal sulcus; STS, superior temporal sulcus; ITS, inferior temporal sulcus.