Initial dip

Definition: The initial dip describes a transient negative response that can be sometimes observed in blood-oxygenation level-dependent (BOLD) / hemodynamic signals. It is assumed to reflect the preliminary stages of the neural metabolic response that causes a transient decrease in oxygenated hemoglobin just prior to the much larger ensuing hemodynamic response leading to an increase in focal oxygenation. The initial dip has been subject to substantial debate because it cannot always be observed. Many factors likely contribute to whether it appears and to what degree, including physiological conditions, participant age, experimental methodologies, species, regions, data analysis. Nethertheless, the initial dip is modeled as part of the canonical hemodynamic response function for BOLD fMRI analyses.

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References: https://doi.org/10.1016/j.neuroimage.2012.03.005

https://doi.org/10.1016/j.neuroimage.2012.03.005

https://doi.org/10.3389/fnbot.2018.00069

https://doi.org/10.1364/BOE.8.000367

Related terms: blood-oxygenation level-dependent (BOLD) response, hemodynamic response, hemodynamic response function