Scientists, including one of Indian-origin, have found that the seemingly erratic behaviour of serial killers conforms to the same mathematical pattern obeyed by earthquakes, avalanches, stock market crashes and many other sporadic events.
The study, conducted by Mikhail Simkin and Vwani Roychowdhury, electrical engineers from the University of California, Los Angeles, modelled the behaviour of Andrei Chikatilo, a gruesome murderer who took the lives of 53 people in Rostov, Russia between 1978 and 1990.
Though Chikatilo sometimes went nearly three years without committing murder, on other occasions, he went just three days. The researchers found that the seemingly random spacing of his murders followed a mathematical distribution known as a power law.
When the number of days between Chikatilo's murders is plotted against the number of times he waited that number of days, the relationship forms a near-straight line on a type of graph called a log-log plot, Live Science reported.
It's the same result scientists get when they plot the magnitude of earthquakes against the number of times each magnitude has occurred and the same goes for a variety of natural phenomena.
The power law outcome suggests that there was an underlying natural process driving the serial killer's behaviour.
Simkin and Roychowdhury hypothesize that it's the same type of effect that has also been found to cause epileptics to have seizures. The psychotic effects that lead a serial killer to commit murder "arise from simultaneous firing of large number of neurons in the brain."
In the brain, the firing of a single neuron can potentially trigger the firing of thousands of others, each of which can in turn trigger thousands more. In this way, neuronal activity cascades through the brain.
Most of the time, the cascade is small and quickly dies down, but occasionally, after time intervals determined by the power law, the neuronal activity surpasses a threshold.
In epileptics, a threshold-crossing cascade of neurons induces a seizure. And if the Simkin and Roychowdhury's theory is right, a similar buildup of excited neurons is what flooded the Rostov Ripper with an overwhelming desire to commit murder. Sometimes he went years without his neurons crossing the threshold, other times, just days.
When the researchers factored a delay into their model to account for the time it took for Chikatilo to plan his next attack, and when they treated his murders as having had a sedative effect on him by damping down the activity of his neurons, their model fit strongly with his murder pattern.
James Fallon, a neuroscientist at UC Irvine who studies the brains of psychopaths, said the new findings are well-aligned with prior observations about serial killers, many of whom seem to behave similarly to drug addicts.
In both cases, Fallon said, withdrawal from their addiction "builds and builds and then hits a threshold trigger point, after which they go on a spree to release that 'longing'."
As with drug addiction, withdrawal from killing may cause a buildup of hormones in a part of the brain called the amygdala, "and this very, very unpleasant feeling can only be reversed by acting out whatever the addicting stimulus might be."
The study has been submitted to Biology Letters.
