Attenuation of High-Frequency (50–200 Hz) Thalamocortical Electroencephalographic Rhythms by Isoflurane in Rats Is More Pronounced for the Thalamus Than for the Cortex
Bibliographic record
Abstract
BACKGROUND: Thalamocortical electroencephalographic rhythms in gamma (30-80 Hz) and high-gamma (80-200 Hz) ranges have been linked to arousal and conscious processes. We have recently shown that propofol causes a concentration-dependent attenuation of the power of thalamocortical rhythms in the 50 to 200 Hz range and that this effect is far more pronounced for the thalamus. To determine whether similar attenuation occurs with other anesthetics, we characterized the concentration-effect relationship of the inhaled anesthetic isoflurane on the spectral power of these rhythms. METHODS: Local field potentials were recorded from the barrel cortex and ventroposteromedial thalamic nucleus in 9 chronically instrumented rats to measure spectral power in the gamma/high-gamma range (30-200 Hz). Rats were placed in an airtight chamber and isoflurane was administered at 0.75%, 1.1%, and 1.5% concentrations. Spectral power was assessed during baseline, at the 3 isoflurane concentrations after 30 minutes for equilibration, and during recovery over 4 frequency bands (30-50, 51-75, 76-125, and 126-200 Hz). Unconsciousness was defined as sustained loss of righting reflex. Multiple linear regression was used to model the change in power (after logarithmic transformation) as a function of concentration and recording site. P values were corrected for multiple comparisons. RESULTS: Unconsciousness occurred at the 1.1% concentration in all animals. Isoflurane caused a robust (P ≤ 0.008) linear concentration-dependent attenuation of cortical and thalamic power in the 30 to 200 Hz range. The concentration-effect slope for the thalamus was steeper than for the cortex in the 51 to 75 Hz (P = 0.029) and 76 to 200 Hz (P < 0.001) ranges but not for the 30 to 50 Hz range (P = 0.320). Comparison with our previously published propofol data showed that slope for cortical power was steeper with isoflurane than with propofol for all frequency bands (P = 0.033). For thalamic power, the slope differences between isoflurane and propofol were not statistically significant (0.087 ≤ P ≤ 0.599). CONCLUSIONS: Isoflurane causes a concentration-dependent attenuation of the power of thalamocortical rhythms in the 30 to 200 Hz range, and this effect is more pronounced for the thalamus than for the cortex for frequencies >50 Hz. In comparison with propofol, isoflurane caused a greater attenuation in the cortex, but the effects on the thalamus were similar. Isoflurane and propofol cause common alterations of fast thalamocortical rhythms that may constitute an electrophysiologic signature of the anesthetized state.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".