Abstract
Changes in BOLD signals are sensitive to the regional blood content associated with the vasculature, which is known as V0 in hemodynamic models. In previous studies involving dynamic causal modeling (DCM) which embodies the hemodynamic model to invert the functional magnetic resonance imaging signals into neuronal activity, V0 was arbitrarily set to a physiolog-ically plausible value to overcome the ill-posedness of the inverse problem. It is interesting to investigate how the V0 value influences DCM. In this study we addressed this issue by using both synthetic and real experiments. The results show that the ability of DCM analysis to reveal information about brain causality depends critically on the assumed V0 value used in the analysis procedure. The choice of V0 value not only directly affects the strength of system connections, but more importantly also affects the inferences about the network architecture. Our analyses speak to a possible refinement of how the hemody-namic process is parameterized (i.e., by making V0 a free parameter); however, the conditional dependencies induced by a more complex model may create more problems than they solve. Obtaining more realistic V0 information in DCM can improve the identifiability of the system and would provide more reliable inferences about the properties of brain connectivity.
Highlights
Dynamic causal modeling (DCM) is widely employed to explore causality between neural systems based on neuroimaging data obtained using methods such as electroencephalography (EEG), magnetoencephalography (MEG), and functional magnetic resonance imaging[1,2,3]
Changes in BOLD signals are sensitive to the regional venous blood volume fraction, which is represented as the physiological parameter V0 in the hemodynamic model[13]
This can result in the active domains that are subject to dynamic causal modeling (DCM) analysis being overly influenced by those areas with large blood contents[14]
Summary
Modeling and System Identifiability received: 08 February 2016 accepted: 17 June 2016 Published: 08 July 2016. Changes in BOLD signals are sensitive to the regional venous blood volume fraction, which is represented as the physiological parameter V0 in the hemodynamic model[13]. This can result in the active domain of the BOLD signal often being overly influenced. The results show that V0 plays a leading role in driving the uncertainty of the hemodynamic model output, especially during a positive BOLD response Calibrating this parameter is of great importance for increasing the system identifiability[18]. We approached the problem from a purely mathematical and modeling perspective, and did not consider the physiological mechanism underlying the BOLD contrast
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