Dr. Francis Crick, the Nobel-winning co-discoverer of DNA structure and creator of The Astonishing Hypothesis.

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The molecular biologist Francis Crick, one half of the research team that discovered the structure of DNA, later in his career came up with what he called The Astonishing Hypothesis. It is, crudely put, the idea that every aspect of human consciousness -- from affinity for one's family, to a belief in God, to the experience of the color green -- is merely the result of electrical activity in our brains' neural networks. As he wrote in 1994, "You're nothing but a pack of neurons" [source: Crick].

At the basis of our conscious experience are chemicals called neurotransmitters. These chemicals generate electrical signals that form the means by which neurons communicate with one another and ultimately form neural networks. When we stimulate these networks, we experience the physical sensations and emotions that make up our lives. We store these as memories to be recalled when the neural networks that store them are activated once more.

The idea may be a bit glum, but it forms the basis of the idea that the electrical activity in the brain is the detectable trace of our conscious experience. By correlation, then, so long as we can detect this electrical activity -- through the use of technology like electroencephalography (EEG), which measures brain waves -- we can assume that a person is experiencing consciousness. This is what makes a 2011 study from Radboud University Nijmegen in the Netherlands so troubling.

To determine whether decapitation, a common method of euthanizing lab rats, is humane, the researchers connected an EEG machine to the brains of rats, decapitated them and recorded the electrical activity in the brain after the event. The Dutch researchers found that for about four seconds after being separated from the body, the rats' brains continued to generate electrical activity between the 13 to 100-Hertz frequency band, which is associated with consciousness and cognition, defined as "a mental process that includes thinking" [source: Cleveland Clinic].

This finding suggests that the brain can continue to produce thoughts and experience sensations for at least several seconds following decapitation -- in rats, at least. Although findings in rats are commonly extrapolated onto humans, we may never fully know if a human remains similarly conscious after the head is lost. As author Alan Bellows points out, "Further scientific observation of human decapitation is unlikely" [source: Bellows].

Yet the annals of medicine following the invention of the guillotine have some very interesting scientific observations of human decapitation. These suggest it is possible to remain conscious after losing one's head. First, let's look at how we've removed heads in the past.