fMRI and Anesthesia

Abstract

BOLD activation studies discussed vary in the anesthetic agent studied (propofol, sevoflurane, and isoflurane), the concentration of the anesthetic (mostly under 0.5MAC or equivalent doses), and the activation paradigm/functional activation. The data analysis technique also differs between the studies. Notwithstanding these variations, the results can be summarized as follows: Higher order association cortices are more sensitive to anesthesia. Higher order regions processing language and semantics (regions in the frontal cortex) are affected at a lower concentration of anesthetic as compared with regions processing auditory stimuli. Whereas primary visual activation regions in the visual cortex and the thalamus are less sensitive, higher order visual spatial attention regions in the parietal cortex are more sensitive to anesthesia. In most studies, the loss of consciousness (no response to call) is achieved at or below 0.5MAC of anesthesia.

Frequency- and State-Dependent Network Effects of Electrical Stimulation Targeting the Ventral Tegmental Area in Macaques

“…The discrepancy between awake and anesthetized preparations could be attributed to several factors. First of all, anesthesia can have a general effect on the pattern and amplitude of the recorded fMRI signals ( Barttfeld et al 2015 ; Tang and Ramani 2016 ). In addition, the VTA may be a particularly peculiar target, as it could play a central role in maintaining or switching mental states.…”

Diet matters: Glucocorticoid-related neuroadaptations associated with calorie intake in female rhesus monkeys

“…Finally, despite the low levels of anesthesia used in this study, there may be potential isoflurane effects on BOLD signal compared to studies investigating awake states. However, the dose of isoflurane used in this study (and higher doses) has previously been used to report coherent patterns of BOLD fluctuations in rhesus macaques, including sensory, motor, visual and cognitive-task related systems (Birn et al, 2014; Hutchison et al, 2013; Li et al, 2013a; Tang and Ramani, 2016; Vincent et al, 2007). Future studies are necessary to understand the impact of psychosocial stressor exposure and the dietary environment on reward pathways and appetite regulation in males.…”

“…and intubation to ensure lack of motion artifacts. This dose (and higher doses) of isoflurane has previously been used to report coherent patterns of BOLD fluctuations in rhesus macaques, including sensory, motor, visual and cognitive-task related systems (Birn et al, 2014; Hutchison et al, 2013; Li et al, 2013a; Tang and Ramani, 2016; Vincent et al, 2007). Importantly, these patterns are similar to those observed in awake, behaving monkeys (Vincent et al, 2007).…”

Long-term alterations in brain and behavior after postnatal Zika virus infections in infant macaques

“…Third, only female subjects were studied, and there may be sex differences in the impact of ZIKV infection as has been recently reported in mice 78 . Fourth, there are several limitations to rs-fMRI which should be noted: (1) FC was obtained under anesthesia, but we note that isoflurane doses were kept below those used in previous studies reporting patterns of coherent BOLD fluctuations similar to the awake state, including in sensory and visual systems [79][80][81][82] ; and (2) our design does not allow to establish causality between the alterations in structural and functional brain measures and behavioral/cognitive alterations or to specific physiological, cellular, or molecular brain maturational processes, which will need to be addressed in future studies. Additional studies are needed to substantiate our findings regarding postnatal ZIKV infection, which should include larger sample sizes of males and females and multiple virus strains reflecting the diversity of this infection.…”

“…Animals were scanned in the supine position in the same orientation, achieved by placement and immobilization of the head in a custom-made head holder via ear bars and a mouthpiece. After initial telazol induction and intubation, scans were collected under isoflurane anesthesia (0.8 to 1%, inhalation, to effect), kept at the lowest dose possible to minimize effects of anesthesia on BOLD signal [79][80][81][82] . End-tidal CO2, inhaled CO2, O2 saturation, heart rate, respiratory rate, blood pressure, and body temperature were monitored continuously and maintained during each MRI session.…”