Blood oxygenation level dependent (BOLD) response, which is measured by functional magnetic resonance imaging (fMRI), is known to be a combination of various vascular parameters, among which deoxy-hemoglobin is argued to be a major contributor. Functional near infrared spectroscopy (fNIRS), though being limited in its spatial resolution, provides a promising tool to study cortical activations, due to its specificity of independent measurement of blood parameters (Oxy, De-oxy and Total Hemoglobin), high temporal resolution and ease of use. To study the close relationship between these imaging modalities, a finger tapping task with stimulus durations (2, 4, 8 & 16 sec) with variable inter-stimulation intervals was chosen to compare spatio-temporal properties and non-linearity of BOLD signal with HbO, HbR and HBT signal. This helped determine what parameter (HbO, HbR and HbT) BOLD signals correlate to most and how factors like neural adaptation that cause non-linearity can affect the hemodynamic behavior. It investigates the non-linearity in HbO, HbR and HbT concentrations as compared to BOLD signal obtained using simultaneous fNIRS and fMRI measurement. Investigating non-linearity in hemodynamic response could provide a better understanding of neuronal function by modeling neural adaptation. The paper also discusses a method to model the neural adaptation and hemodynamic response.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.