Neurophysiological methods for evaluation of infants’ sensory processing

Early infancy is a critical period for brain development, during which medical adversities can have lifelong consequences. Neurodevelopmental disorders often first manifest as sensorineural defects. However, assessing these in infants is challenging, as tests designed for older children are not yet suitable for developing babies. Therefore, there is a pressing need for innovative diagnostic tools for objective evaluation of sensory processing, offering insights into developing brain function and facilitating early interventions and care. This Thesis presents new technical approaches to assess infants’ sensory systems by characterizing electroencephalography (EEG) responses to visual and somatosensory stimulation. Additionally, eye tracking was employed in a behavioral task to study the mechanisms of visual attention and face preference for various facial expressions. The research incorporated advanced computational techniques—such as source reconstruction and connectivity analysis—integrated with task designs that systematically targeted specific aspects of sensory processing. In Study I, healthy 5- and 7-month-old infants were examined in a face-distractor competition paradigm, utilizing newly developed dynamic eye tracking metrics. Results revealed age-specific differences in gaze disengagement from faces, especially those with fearful expressions, indicating sensitivity to developmental changes. Studies II and III assessed cortical visual processing in healthy 3–5-month-old infants using cyclic orientation reversal, global form, and global motion stimuli. Eye tracking integrated with the visual stimulus presentation enabled detection of occipital steady-state EEG responses in 92–100% of the recordings, substantially exceeding detection rates reported in the literature. Connectivity analysis of these responses revealed recruitment of widespread functional networks extending also beyond the traditional visual streams, with a global form-related network metric correlating positively with later cognitive performance. Study IV examined proprioceptive EEG responses in asphyxiated neonates during repetitive hand movement stimulation. All neonates produced contralateral responses with vast cortico-cortical recruitment, though the extent of activation was reduced in cases with hypoxic-ischemic encephalopathy. Overall, the studies demonstrate significant potential of the presented methods for early assessment of sensory processing and related neurocognitive development. However, high individual variability suggests that these tools may not yet be ready for clinical use. Further research is still needed with larger and more heterogeneous cohorts.