The pilot study was carried out at Huelva Prison in southwestern Spain and saw the technique – known as transcranial direct current stimulation, or tDCS – carried out on 41 violent prisoners, 15 of them serving murder sentences.
Spain’s interior ministry announced that the experiment had been called off the day after preliminary details of the study, which tested the impact of small electrical currents passed into the prefrontal cortex of volunteer male prisoners, were published in the New Scientist.
The trial, which had the approval of prison officials and university ethics committee wanted to determine whether TDCS deliver to the frontal lobe in three 15-minute sessions had an effect on levels of aggression reported by the male inmates.
Phase two of the study was due to commence this month.
But an interior ministry spokesman explained that permission for the experiments had been given by the previous government and would now be suspended as a precaution pending a full investigation into the matter.
The treatment, which is supposed to be painless, involves strapping electrodes to the inmates head and turning on an electric current for 15 minutes per day over the course of three days.
The prisoners are required to fill out questionnaires before and after treatment rating their feelings of anger.
Samples of each participant's saliva are also tested for cortisol levels – a hormone that increases with stress and can indicate aggressive tendencies.