Visual sensory determinants of EEG activity in neonates receiving intensive care

INTRODUCTION: Cortical activity is crucial for neural organisation during early life, especially in vulnerable infants who have suffered neurological compromise and/or require intensive care. However, its sensory determinants are poorly understood. In hospital, acutely unwell infants sometimes wear eye shields. We used this natural experiment to test the hypothesis that reduction of external visual inputs will attenuate occipital cortical activity. METHODS: We analysed 9-channels video-EEG from 18 sleeping neonates (median gestational age 39 weeks (IQR 36-40); 14/18 had mild-moderate hypoxic-ischemic encephalopathy). We compared power spectral density of EEG between eye shield vs. no eye shield, matched by vigilance state, any neuroactive medications, and within four hours (total 31 test occasions). We cross-referenced these data against power spectral changes of EEG to another visual stimulus: pupillary examination with a torch light (18 neonates, 7 overlapping with eye shield analysis: total 29 neonates had visual sensory data analysed). RESULTS: Gamma (>30 Hz) but not slower frequency power was slightly lower on average during the eye shield condition - specifically at the occipital region - but this did not survive adjustment for multiple comparisons. There was no association between infants' EEG responsivity to the eye shield and torch light stimuli. CONCLUSION: EEG activity was insensitive to reduction of external visual inputs in this sample of acutely unwell infants, even when integrity of their retina-visual cortex pathway could be confirmed by response to torch light. In this population, the majority of visual cortical activity may be endogenously generated, and therefore not modulated by an eye shield intervention.