Data-driven optimization of preschoolers' hemodynamic response in a VR setup: advancing analytic methods for children's fNIRS naturalistic data with the AICopt method.

Significance: Naturalistic fNIRS data acquired on children enable studying real-world behaviors but challenge standard analysis methods such as block averaging and general linear model (GLM). In naturalistic paradigms, events often overlap, whereas children's hemodynamic responses generally deviate from the adult canonical model, possibly leading to responses' misattribution and low sensitivity. Aim: We aim to reduce the risk of misattributing neural responses to stimuli by refining the shape and timing of the hemodynamic response function (HRF) for each brain region and event type in a data-driven framework, addressing cases where overlapping responses lead to neural responses being mistakenly assigned to the wrong stimulus, distorting results, and leading to misleading conclusions. Approach: We introduce a data-driven HRF optimization procedure (AICopt) that enables GLM-based analyses when the HRF is unknown. We evaluated the AICopt approach in 40 preschoolers (3 to 5 years) within a virtual-reality paradigm, featuring emotionally relevant and neutral events followed immediately by choices, without fixed inter-trial baselines. Then, we compare its performance with what is obtained using the block-averaging method and canonical HRF model-based GLM analysis. Results: AICopt yielded activation patterns that converged with block-averaging results for events while avoiding likely spurious choice-related activations seen with the canonical GLM. Overall, the use of data-driven HRFs improved sensitivity and reduced misattribution relative to the fixed canonical HRF in this overlapping-event design. Conclusions: Our results suggest that data-driven HRF modeling is a necessary step when analyzing fNIRS data from atypical populations such as young children, particularly in studies employing naturalistic setups. The presented AICopt method represents a possible approach to adapt GLM analyses to overlapping events and diverse populations, improving accuracy and interpretability of the obtained activation maps, and offering a reusable workflow for child fNIRS datasets collected in nonstandard setups.