Assessing parameter identifiability for dynamic causal modeling of fMRI data.
Deterministic dynamic causal modeling (DCM) for fMRI data is a sophisticated approach to analyse effective connectivity in terms of directed interactions between brain regions of interest. To date it is difficult to know if acquired fMRI data will yield precise estimation of DCM parameters. Focusing on parameter identifiability, an important prerequisite for research questions on directed connectivity, we present an approach inferring if parameters of an envisaged DCM are identifiable based on information from fMRI data. With the freely available "attention to motion" dataset, we investigate identifiability of two DCMs and show how different imaging specifications impact on identifiability. We used the profile likelihood, which has successfully been applied in systems biology, to assess the identifiability of parameters in a DCM with specified scanning parameters. Parameters are identifiable when minima of the profile likelihood as well as finite confidence intervals for the parameters exist. Intermediate epoch duration, shorter TR and longer session duration generally increased the information content in the data and thus improved identifiability. Irrespective of biological factors such as size and location of a region, attention should be paid to densely interconnected regions in a DCM, as those seem to be prone to non-identifiability. Our approach, available in the DCMident toolbox, enables to judge if the parameters of an envisaged DCM are sufficiently determined by underlying data without priors as opposed to primarily reflecting the Bayesian priors in a SPM-DCM. Assessments with the DCMident toolbox prior to a study will lead to improved identifiability of the parameters and thus might prevent suboptimal data acquisition. Thus, the toolbox can be used as a preprocessing step to provide immediate statements on parameter identifiability.
Center for Data Analysis and Modelling (FDM), University of Freiburg Freiburg, Germany ; Department of Physics, University of Freiburg Freiburg, Germany ; Department of Radiology, Medical Physics, University Medical Center Freiburg Freiburg, Germany.
Carolin
C
Arand
Department of Psychiatry and Psychotherapy, University Medical Center Freiburg Freiburg, Germany ; Freiburg Brain Imaging Center, Departments of Neurology and Psychiatry, University Medical Center Freiburg Freiburg, Germany ; Laboratory for Biological and Personality Psychology, Department of Psychology, University of Freiburg Freiburg, Germany.
Elisa
E
Scheller
Center for Data Analysis and Modelling (FDM), University of Freiburg Freiburg, Germany.
Benjamin
B
Seeber
Center for Data Analysis and Modelling (FDM), University of Freiburg Freiburg, Germany ; Department of Physics, University of Freiburg Freiburg, Germany ; BIOSS Center for Biological Signaling Studies, University of Freiburg Freiburg, Germany.
Jens
J
Timmer
Department of Psychiatry and Psychotherapy, University Medical Center Freiburg Freiburg, Germany ; Freiburg Brain Imaging Center, Departments of Neurology and Psychiatry, University Medical Center Freiburg Freiburg, Germany ; Department of Neurology, University Medical Center Freiburg Freiburg, Germany.
Stefan
S
Klöppel
Department of Physics, University of Freiburg Freiburg, Germany ; Department of Neurology, University Medical Center Freiburg Freiburg, Germany ; Institute for Complex Systems and Mathematical Biology, King's College, University of Aberdeen Aberdeen, UK.
Björn
B
Schelter
dynamic causal modeling; functional magnetic resonance imaging; model parameters; parameter identifiability; profile likelihood