Theta and theta-gamma coupling processes as an index of building object representations in the infant brain

• In Event: The theta rhythm as a neural signature of early learning processes

Abstract

Recent work attempting to understand the neural mechanisms underlying learning in infancy have pointed to brain activity in the 3 – 6 Hz theta band as a candidate for driving information encoding (Begus & Bonawitz, 2020). First indications show that theta power, but not alpha power, is increased for unexpected compared to expected events in infants (Köster, Langeloh & Hoehl, 2019), and that theta modulation in infancy predicts cognitive ability in later childhood (Braithwaite, Jones, Johnson & Holmboe, 2020), suggesting that the theta rhythm may indeed constitute an important index of learning in infants.
In adults, theta power has long been associated with memory formation (see Klimesch, 1999) and is increased for visual stimuli that were later remembered, compared to stimuli that were later forgotten (Friese et al., 2013). In particular, the coupling between the theta phase and gamma amplitude has been shown to be responsible for binding perceptual features to form representations, for example, during the formation of visual associations between pictures and colours (Köster, Finger, Graetz, Kater & Gruber, 2018).
However, much less is known about information encoding in infancy, and theta-gamma coupling has not been examined in infants due to methodological difficulties, such as contamination of the EEG signal in the gamma range by microsaccades (Köster, 2016) and low signal-to-noise ratios in infant EEG data (Hoehl & Wahl, 2012). Since infants are in the process of building novel representations of their environment, it is an intriguing empirical question whether they integrate incoming information based on similar neural processes as adults.
The current study examines theta power and theta-gamma coupling for novel objects compared to familiar objects in 48 infants (6;12 – 8;04 months old) in order to examine the neuronal processes related to forming new representations.
At the beginning of the experiment, infants were familiarised with four stimuli. They then saw interleaved trials showing either one of these familiar four images (familiar objects) or entirely new images (novel objects; see Figure 1 for study design). The EEG was recorded from 29 channels with an EasyCap using Cz as an online reference, and transformed using Morlet wavelets to time-frequency space in order to examine spectral power.
Based on the findings in adults, we expected that infants would show higher theta power for novel compared to familiar stimuli and that theta-gamma coupling would be higher for novel compared to familiar stimuli.
All data has been collected, and preliminary analysis from a subsample of infants (N = 10) show increased occipital and frontal theta for novel compared to familiar objects (see Figure 2). This is in line with the idea that the theta rhythm plays a critical role for information encoding and memory formation in the current sample of infants and the present design. We will further analyse cross-frequency coupling processes and hypothesize higher theta-gamma coupling, between frontal and parietal networks for the processing of novel versus familiar objects.

Authors

• Emma K Ward, Freie Universität Berlin
  Presenting Author

• Ezgi Kayhan, University of Potsdam
  Non-Presenting Author

• Christian Kliesch
  Non-Presenting Author

• Radoslaw Cichy, Freie Universität Berlin
  Non-Presenting Author

• Stefanie Hoehl, University of Vienna
  Non-Presenting Author

• Moritz Köster, Freie Universität Berlin
  Non-Presenting Author