Figure 9.

The functional characteristics (qualifiers) and MIND signature (identifier) of a specific brain state induced by an anesthetic protocol. The aim of anesthesia in fMRI is to induce stable sedation, while maintaining a brain state that approximates an awake, calm state. The protocol may be either mono-anesthetic (drug a; dose x) or multimodal (drug a, b, c; dose x, y, z). Qualifiers are defined as functional characteristics of an intermediate brain state that has been induced and maintained by the use of anesthesia: The cortical EEG signature permits to monitor anesthetic depth, to evaluate arousability by challenging the stability of a brain state via nociception or stress, and to probe stimulus-response features of sensory evoked potentials (SEP). Hemodynamic translation can be evaluated via fMRI, whereas shape and magnitude of the hemodynamic response function (HRF) provide information about anesthesia-induced vasomodulation. Anesthetic effects on functional connectivity (FC) across the brain can be assessed based on correlation matrices that depict interrelations of cortical and subcortical areas, including anticorrelations, and the dynamic repertoire of recurring sets of FC patterns over time. FC has great value as an identifier of a particular brain state and the integrity of its qualifiers. A fingerprint-like FC signature pattern can be used to unambiguously identify maintained intermediate brain states under anesthesia and communicate them across labs. This signature pattern is termed the maintained, intermediate neurophysiologically-determined (MIND) signature. Flanking tasks in fMRI with resting-state scans will permit a researcher to monitor the maintenance or variations in the brain state under anesthesia throughout the fMRI experiment.