Several seconds before we utter a sound, signals about the content and form of the utterance can be read from our brain. This is reported by a research team led by Prof. Markus Siegel from the Hertie Institute for Clinical Brain Research, the University of Tübingen and the University Hospital in Tübingen. The team investigated whether the content and production of language are processed separately in the brain. With the help of modern imaging in the form of magnetoencephalography (MEG), the researchers were able to identify the content of the brain activity independently of the motor production – and thus also to predict which of two fixed sounds the test subjects would utter immediately. They published their findings in the journal PNAS.
We all know it: the inner voice that silently accompanies us through everyday life. It suggests that these types of thoughts arise separately from the motor process of speech. But how does our brain process language content and production? That was the question the Tübingen research team was working on.
“We recorded brain activity in subjects while they performed a simple vocalization task,” said study leader Siegel. They had to imagine one of two vowels or utter it aloud. They were shown on a screen which task they were to perform in each experimental run.
The researchers use magnetoencephalography (MEG) to measure brain activity. MEG makes it possible to measure human brain activity non-invasively by recording the magnetic fields generated by brain activity outside the head. Since these magnetic fields are many times smaller than the earth’s magnetic field or the magnetic fields caused by electrical devices, the measurement at the Tübingen MEG center was carried out using highly sensitive magnetic field sensors in a special magnetically shielded room. The researchers then subjected the data to an advanced statistical pattern analysis.
With success: “We managed to identify the vowel in the brain signals that the test subjects should vocalize – a few seconds before the execution,” says the first author of the study, Vera Voigtländer. “This was independent of whether they later said it out loud or just imagined it.” This indicates that the language content is represented abstractly in the brain. In this way it can be generalized across different forms of production – such as the silent inner voice or loud verbal utterances.
The scientists dismissed the fear that they could read minds with their method. “The measurements are very complex. The MEG takes up a lot of space, the signals are very weak, and the sounds examined are not complex thoughts,” explains Siegel. However, the results of the study provide fundamental insights into the neural processes that underlie the production of language – an essential human ability that can be impaired in various diseases. “In this way, the results of the study could contribute in the long term to developing speech prostheses and making them more efficient,” explains co-author Professor Dr. Steffen Hage from the ENT clinic at the University Hospital in Tübingen. “In the long term, we want to study different building blocks of language. We have currently only analyzed individual vowels,” says Siegel. “The next step is to look at how the brain processes more complex vocalizations.”
How to measure the electrical signals of brain cells
The magnetoencephalography (MEG) is an imaging technique used to measure electrical activity in the brain. It works by sensing the tiny magnetic fields created by the brain cells’ electrical signals. With the help of special sensors placed around the head, the MEG can precisely record the activity in different regions of the brain. This enables researchers to study neuronal processes and dysfunctions in the brain, such as in epilepsy or neurological disorders. MEG offers high temporal resolution and is non-invasive, making it an important tool for studying the brain.