A light micrograph of a section of a whole mouse brain, with nerve cells colourfully labelledARTHUR CHIEN/SCIENCE PHOTO LIBRARY Electrical synapses that carry messages through the brain have been artificially engineered in mammals for the first time, altering their behaviour. This could have potential for preventing or treating a range of mental health conditions, including obsessive compulsive disorder (OCD). Connections, or synapses, between nerve cells are either electrical or chemical. Chemical ones, which are more common in mammals, involve molecules called neurotransmitters, whereas electrical synapses rely on proteins called connexins.