Human speech comes in countless varieties: When people talk to close friends or partners, they talk differently than when they address a physician. These differences in speech are quite subtle and hard to pinpoint.

In a recent special issue of the journal Frontiers in Human Neuroscience, Johanna Derix, Dr. Tonio Ball, and their colleagues from the Bernstein Center and the University Medical Center in Freiburg report that they were able to tell from brain signals who a person was talking to. This discovery could contribute to the further development of speech synthesizers for patients with severe paralysis.

In contrast to the experimental research common in human neuroscience, the scientists studied natural, non-experimental behavior. Patients who, for medical reasons, had electrodes implanted underneath their skull allowed their brain activity to be recorded during daily life in the hospital. The Freiburg researchers compared data recorded during natural conversations that the patients had with their physicians and their life partners. They found pronounced differences in the anterior temporal lobe, a brain area well known for its significance in social interaction. Several components of neural signals that are detectable on the brain surface can convey such information.

"This study is only the first step towards elucidating the neural basis of human everyday behavior," explains the neuroscientist and physician Tonio Ball. "Such investigations will become especially important in developing new neurotechnological treatment options for patients with impaired motor and language functions that work in real life situations." The restoration of speech production becomes necessary in some forms of neurological diseases and chronic paralysis. A computer could synthesize speech for patients suffering from such conditions by using their brain signals. Information on who the patient is addressing could help the device to select the degree of formality -- and to prevent it from calling the doctor "darling."