Science1 publisher2 min readPublished
Anesthetics fragment brain activity the same way in six species spanning 700 million years of evolution
Andrea Luppi's Oxford-led team found that general anesthetics fragment brain activity the same way in six species, nematodes and humans among them. The shared pattern points to a common end state in the brain, but which molecular targets the drugs hit is still unknown.
The Scientist · Science desk
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What happened
- The six datasets came from humans, macaques, marmosets, mice, zebrafish and nematodes, and each species was anesthetized with its own drugs.
- Mammals were measured with fMRI, a blood-flow proxy, while zebrafish and nematodes were engineered so that firing neurons lit up with calcium.
- Under anesthesia, brain regions kept working but coordinated less with each other, and activity over time lost its usual predictable sequences.
- Anesthesiologists George Mashour and Zirui Huang, who were not involved, wrote that the odds of the pattern appearing in all six species by chance are vanishingly small.
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Why it matters
- constraint Because the drugs differed by species, the shared profile cannot settle which molecular sites anesthetics act on, so that question still needs drug-by-drug work.
- capability With the same profile visible in calcium-imaged zebrafish and nematodes, researchers can study how anesthetic fragmentation arises in animals whose individual neurons can be watched directly.
- precedent Mashour and Huang's fragmentation account gives later studies of anesthesia and consciousness a specific claim to test against the idea of the brain simply switching off.
Pooling data gathered with different drugs, species and instruments would normally add noise. Luppi's team used those differences to screen out effects that belong to only one setup. "Focusing on effects that are consistently shared across multiple anesthetics and species allows us to exclude physiological or methodological confounds specific to any one drug, species, or imaging modality, and instead triangulate on potential neural underpinnings of what they share: breakdown of responsiveness to the environment," they wrote [6]. Four of the six species were scanned with fMRI and two were imaged neuron by neuron [15]. Any feature that counted had to show up under both methods.
Surgeons have used general anesthesia since its first public demonstration in 1846 without a full account of how the drugs work [14]. This study describes one level of that account: how activity across a brain is organised over time. The authors call what they found "an evolutionarily conserved dynamical profile of anesthesia" [9]. The profile is conserved. Because the drugs differed from one species to the next [3], the study cannot show that they share a molecular target.
Mashour and Huang's commentary agrees with that narrower reading. "These findings provide compelling support for a final common pathway of anesthesia: spatiotemporal isolation of local neural activity, in which individual circuits lose their ability to sustain, propagate and integrate information across time and space," they wrote [11]. A final common pathway is a point where separate routes end up. Different drugs could act at different molecular sites and still produce the same fragmented state. "During anesthesia, consciousness is disrupted not because the brain 'turns off' but rather because its activity becomes temporally and spatially fragmented," they wrote [12].
There is also the question of cause. The authors report that the shared signature appears alongside the shared behaviour, isolation from the environment [9]. That is strong evidence the two occur together across very distant animals. It is not yet evidence that fragmentation produces the unresponsiveness. The ScienceAlert account does not list the specific drugs, the number of animals or the size of the effect in each species.
ScienceAlert notes that anesthetics act even on plants and paramecia [13]. Neither has a brain, so whatever the drugs do in those organisms cannot be coordination between brain regions. The outlet also suggests the findings may bear on animal consciousness [16]. I think the defensible claim is narrower for now. Under these drugs, a nematode and a human lose the same pattern of neural activity. What that loss means for a nematode's experience is a separate question.
What to watch
- Experiments that restore coordination between brain regions under anesthesia, or break it without any drug, and check whether responsiveness changes; that would test cause, not co-occurrence.
- Whether the full paper's per-species results show drugs with different known molecular targets producing the same profile at similar effect sizes.
- Whether the profile tracks depth of anesthesia within one species closely enough to be read from patient recordings during surgery.