Whole-head high-density diffuse optical tomography to map infant audio-visual responses to social and non-social stimuli.

Infancy is a time of rapid brain development. High-density diffuse optical tomography (HD-DOT) is an optical neuroimaging method that maps changes in cortical haemoglobin concentration, a marker of functional brain activation. Recent years have seen a huge advance in wearable hardware for HD-DOT, however previous headgear has only been capable of sampling specific areas of the cortex. In this work, we aimed to develop headgear capable of sampling across the whole infant scalp surface and to conduct a proof-of-concept demonstration of whole-head HD-DOT in infants aged 5 to 7 months. We developed a whole-head infant implementation of the high-density LUMO design developed by Gowerlabs Ltd. (UK). HD-DOT data were collected from a cohort of infants (N = 16) during the presentation of a screen-based paradigm assessing social processing. Using whole-head HD-DOT, we mapped activity across the entirety of the optically-accessible cortex which far exceeds coverage achieved by previous infant optical neuroimaging methods. We found activity in temporal regions which corroborates previous research. Further, we mapped activity in regions outside those typically sampled in infant research using social processing paradigms, finding activation in regions across the occipital, parietal, and frontal cortices as well as an apparent inverted response in sensorimotor regions. Following this proof-of-concept, we envisage that whole-head HD-DOT will be applied to map the interaction between different regions of the brain, opening new avenues to map activity in the awake infant brain to better understand the trajectory of typical and atypical neurodevelopment.