Plasticity in Developing Brain: Active Auditory Exposure Impacts Prelinguistic Acoustic Mapping

Group effects of auditory exposure on latency and amplitude for all three groups at the 7 month post-test. a, Grand average waveforms from 124 electrodes overlaid for AEx (solid line), PEx (dashed line), and NC (dotted line) groups at Fz. Standard (blue) and deviant (red) waves are shown for the control (300 ms ISI) and fast-rate (70 ms ISI) conditions. b, P2 peak amplitudes for all nine electrodes of interest are shown by group (red, AEx; green, PEx; blue, NC) for each tone of the two tone pairs in the 300 ms ISI condition. The four P2 peaks depicted on the x-axis include the P2 responses to the standard pair (two) and from the predeviant standard (one), as well as the P2 peak elicited by the 1200 Hz deviant tone. The AEx group achieved significantly higher amplitudes for the repeated 8oo Hz standard tones compared with the PEx and NC groups. However, all groups had significantly higher amplitudes for the 1200 Hz deviant tone. Bar graphs (error bars indicate SEM) show the mean P2 peak amplitude for each tone. T1, tone 1; T2, tone 2; solid bars, 800 Hz tones; striped bars, 1200 Hz tone. c, P2 peak amplitudes for all nine electrodes of interest by group (red, AEx; green, PEx; blue, NC) for each of the merged tone pairs in the 70 ms ISI condition. Only two P2 peaks are generated at 70 ms ISI. The NC group had significantly lower amplitudes for both the STD (800–800 Hz) and DEV (800–1200 Hz) merged tones compared with those in the AEx and PEx groups. Bar graphs (error bars indicate SEM) show the mean P2 peak amplitude for each tone. T1, Tone 1; T2, tone2; solid bars, STD; striped bars, DEV.

Group differences in latency and amplitude at 70 ms ISI among the three groups at the 7 month post-test. a, Grand average waveforms for all 124 electrodes by group are shown at Fz for the P2 peak on the deviant wave. Highlighted yellow bars on the deviant waveform indicate the location of the maximum P2 peak for each group. Time-locked, age-appropriate topograms to the P2 peak latency by group are also shown. The amplitude scale is shown in microvolts; blue represents negative and red positive activity. A red box around a topogram denotes significantly faster latencies. The AEx group is significantly faster than both the PEx and NC groups, and the PEx group is significantly faster than the NC group. b, Grand average waveforms for all 124 electrodes by group are shown at Fz for the N2* on the deviant wave. Highlighted yellow bars on the deviant waveform indicate the location of the maximum N2* peak for each group. Time-locked, age-appropriate topograms to the N2* peak latency for each group are shown. Amplitude is in microvolts; blue represents negative and red positive activity. A red box around a topogram indicates significantly faster latencies. The AEx and the PEx groups are significantly faster than the NC group.

Group differences in morphology for the 70 ms ISI grand average waveform at the 7 month post-test. a, An exemplar waveform from each of the three 7-month-old groups demonstrates the emergence of additional peaks for the AEx group that are not evident for PEx or NC groups. Emerging double peaks (starred) were seen at the 7 month post-test in the majority (78%) of AEx infants at 7 months of age; 41% of the PEx group and 22% of the NC group (χ² = 8.6, p = 0.01) exhibited this signature maturational profile. b, Morphologically similar double peaks (starred) seen in typically developing 12- and 24-month-old children. (Grand average waveforms at Fz were adapted from Choudhury and Benasich, 2011; plotted at slightly larger scale to accommodate larger-amplitude peaks of the younger infants.) While the double peaks depicted here for the older children are similar morphologically to those seen in the AEx group, typical maturational differences are present for these 12- and 24-month-old children, including faster latencies and smaller amplitudes are seen compared with the 7-month-old children in a.

Generalization to nonexposed stimuli in the multideviant paradigm by group at the 7 month post-test: enhanced processing on the standard wave. a, Grand average waveforms for all 124 electrodes at Fz by group to the STD stimulus in the multideviant generalization paradigm. The P1 peak for the STD waveform is significantly faster for the AEx group (solid line) than for the PEx (dashed line) and NC (dotted line) groups. b, Bar graphs (error bars indicate SEM) depicting significantly faster latency of P1 for the STD in the multideviant generalization paradigm for the AEx group (left) when compared with PEx and NC groups. The AEx group also demonstrated smaller, more mature amplitudes for the P1 and N1 peaks compared with those in the PEx and NC groups. All values are plotted from the mean grand averages at Fz.

Generalization to nonexposed stimuli in the multideviant paradigm by group at the 7 month post-test: enhanced processing on P1 and N1 for all three deviants. a, Bar graphs depict the mean latency of each DEV at each of the nine electrode sites by group. Significantly faster P1 latencies (p < 0.05) are seen for the AEx group (red) for all three deviants and for all nine electrode sites compared with those in the PEx (green) and NC (blue) groups. Significant differences are circled. b, Bar graphs (error bars indicate SEM) show the mean latency of each group by DEV type (gap, duration, frequency). There were significant group interactions for N1 latency. For each deviant, the AEx group was significantly faster at all electrode sites than the PEx and NC groups (p values < 0.05). A significant interaction revealed that the NC group was significantly slower when processing the frequency deviant. All values are plotted from the mean grand averages at F3.