There is no definitive scientific evidence confirming consciousness after decapitation in humans. Studies showing post-decapitation brain activity are primarily based on experiments conducted on rats, in which EEG signals have been observed for a few seconds after decapitation, but this does not mean there is consciousness, as residual electrical activity does not equate to perception, thought, or awareness. The human brain, unlike that of rats, is highly sensitive to the lack of oxygen and entirely dependent on a constant blood supply to maintain consciousness, so when the head is separated from the body, blood pressure collapses immediately, and loss of consciousness is practically instantaneous. Even if some brain cells remain metabolically active for a few seconds before definitive cell death, this does not imply that the person is still conscious or capable of perceiving anything. Movements or twitches observed after decapitation are simply involuntary neuromuscular reflexes caused by residual electrical discharges in the nerves and not signs of consciousness. If the human brain truly remained conscious for several seconds after decapitation, there would be measurable signs of brain activity associated with perception and thought, something that no neurophysiological study in humans has ever demonstrated. The guillotine has historically been considered one of the fastest and least painful execution methods ever used, and the debate over post-decapitation consciousness is more a legacy of popular beliefs and anecdotal observations than a phenomenon supported by scientific evidence.
The EEG in rats after decapitation shows residual activity for about 10-15 seconds, with increases in F50 and F95 frequencies and a decrease in total power (Ptot). Some interpret this data as evidence that consciousness persists, but this hypothesis is problematic when compared with other known states of unconsciousness, such as coma and general anesthesia.
During general anesthesia, the EEG displays distinct patterns, with an increase in slow waves (delta and theta) and a reduction in high-frequency activity, reflecting deep cortical inhibition. Patients under anesthesia do not perceive pain despite having an active EEG, demonstrating that the presence of electrical signals in the brain does not necessarily imply consciousness. In coma, EEG patterns can range from slowed activity to burst suppression and even an isoelectric trace in cases of brain death. Even in reversible coma states, EEG activity is not an indicator of awareness.
This comparison highlights that post-decapitation EEG activity may not be sufficient to prove the persistence of consciousness, as similar signals appear in deeply unconscious states. The main issue with the argument that consciousness persists after decapitation is that EEG is the only available evidence, without proof linking this activity directly to conscious experience. The rapid loss of cerebral perfusion in decapitated rats makes it unlikely that the brain can sustain consciousness beyond a few seconds. If we accept that an anesthetized patient, despite having an active EEG, is unconscious, then the same principle should apply to decapitated rats.