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. 2020 May 19;14:8. doi: 10.3389/fnsys.2020.00008

Figure 2.

Figure 2

Cortical oscillatory signatures of brain states under anesthesia. (A) Changes in oscillatory signatures for increasing doses of propofol and dexmedetomidine measured from the human anterior cortex. With increasing anesthetic depth, oscillation frequencies decrease and synchronize. (B) Distinct oscillatory signatures induced by different anesthetics (upper panel) and dosages (lower panel). The spectrogram represents the spectrum of frequencies in a time and frequency domain, which facilitates the identification of structured frequency bands. (C) Loss of responsiveness (LOR) and connected consciousness (LOC) induced by increasing doses of propofol. LOR is defined by suppression of responses to click and verbal commands (upper panel). Note the occurrence of alpha bands and the absence of slow-delta bands in the phase between LOR and LOC in the spectrogram. The same is true for return of consciousness (ROC) and responsiveness (ROR). In rodents, alpha waves coincide with the loss of righting reflex (LORR), which corresponds to LOR, and slow-delta waves are indicated by a complete loss of movement (LOM), which corresponds to LOC. (D) Brain states may not be fully stable when maintained via anesthesia. Transitions between two or more intermediate states occurred over longer periods of constant isoflurane concentration in rats. This feature has been defined as metastability. Note the logarithmic scale used to highlight the transitions that occur primarily in the lower frequency band (0–10 Hz). Local field potentials (LFP) recording was conducted in the anterior cingulate cortex (ACC). (E) Stimulation (white bars) of dopaminergic neurons of the ventral tegmental area in the rat shifts cortical states under sedation from slow delta (<4 Hz) towards θ power (isoflurane), or towards θ and β power (propofol). Oscillations: slow (<1 Hz), δ (1–4 Hz), θ (4–8 Hz), α (8–15 Hz), β (15–30 Hz), awake-γ (30–80 Hz), ketamine-γ (25–35 Hz), spindle (9–16 Hz). Adapted with permission from (A,B) Purdon et al. (2015); (B, lower panel) Akeju and Brown (2017); (C) Purdon et al. (2013); (D) Hudson (2017), and (E) Solt et al. (2014).