Optimizing Experimental Design for Comparing Models of Brain Function

Abstract

This article presents the first attempt to formalize the optimization of experimental design with the aim of comparing models of brain function based on neuroimaging data. We demonstrate our approach in the context of Dynamic Causal Modelling (DCM), which relates experimental manipulations to observed network dynamics (via hidden neuronal states) and provides an inference framework for selecting among candidate models. Here, we show how to optimize the sensitivity of model selection by choosing among experimental designs according to their respective model selection accuracy. Using Bayesian decision theory, we (i) derive the Laplace-Chernoff risk for model selection, (ii) disclose its relationship with classical design optimality criteria and (iii) assess its sensitivity to basic modelling assumptions. We then evaluate the approach when identifying brain networks using DCM. Monte-Carlo simulations and empirical analyses of fMRI data from a simple bimanual motor task in humans serve to demonstrate the relationship between network identification and the optimal experimental design. For example, we show that deciding whether there is a feedback connection requires shorter epoch durations, relative to asking whether there is experimentally induced change in a connection that is known to be present. Finally, we discuss limitations and potential extensions of this work.

Author Summary

During the past two decades, brain mapping research has undergone a paradigm switch. In addition to localizing brain regions that encode specific sensory, motor or cognitive processes, neuroimaging data is nowadays further exploited to ask questions about how information is transmitted through brain networks. The ambition here is to ask questions such as: “what is the nature of the information that region A passes on to region B”. This can be experimentally addressed by, e.g., showing that the influence that A exerts onto B depends upon specific sensory, motor or cognitive manipulations. This means one has to compare (in a statistical sense) candidate network models of the brain (with different modulations of effective connectivity, say), based on experimental data. The question we address here is how one should design the experiment in order to best discriminate such candidate models. We approach the problem from a statistical decision theoretical perspective, whereby the optimal design is the one that minimizes the model selection error rate. We demonstrate the approach using simulated and empirical data and show how it can be applied to any experimental question that can be framed as a model comparison problem.