Recent research revealed that people who can’t distinguish between two faces might be suffering from a rare condition called "face blindness" which lacks connections in a brain area responsible for recognizing faces. Medically known as prosopagnosia, face blindness takes two forms: acquired and inherited.

Lead researcher, Cibu Thomas, a neuroscientist at Carnegie Mellon University in Pittsburgh, Pennsylvania said that people who develop the condition later in life have usually suffered a stroke or an injury in a brain region important for facial recognition called the fusiform gyrus. The inherited form – which may affect up to one out of 50 people – is far more mysterious. Tests of facial recognition can diagnose inherited prosopagnosiacs, but functional brain scans have revealed few differences between their brains and those of people who can pick out celebrities and loved ones.

Thomas and his colleagues subjected six face-blind subjects to a type of brain imaging which revealed the structural connections that allow distant parts of the brain to communicate. The technique known as diffusion tensor imaging (DTI) revealed wiring differences in the brains of people with synaesthesia, compared to people without the condition.

Researches found that the brains of suffering from prosopagnosia housed fewer connections than controls in two tracts that run smack through the fusiform gyrus; while other parts of their brains showed no such wiring differences, the team found.

Thomas said that slower or noisier neuron signals to and from the fusiform gyrus could explain some cases of face blindness.