What areas of the brain are involved in the linguistic processes underlying speech and listening? Are there large differences between them? Neuroscientists from the Donders Institute for Brain, Cognition and Behaviour at Radboud University Nijmegen are the first to have successfully investigated this question using fMRI and have established that there is a large degree of overlap between the areas involved.
Within the scientific community there is a lot of discussion about whether the brain functions involved in speech production are also involved in the comprehension of speech. In the area of mirror neuron research in particular, a hot topic for the past 15 years, research has viewed the overlap between the areas of the brain involved in speech and listening as reaction and observed action.
However, speaking and listening are more than just action and observation. They also involve linguistic processing. Researchers in the current study mainly focused on this last aspect: which areas of the brain are involved in the semantic (production and the comprehension of meaning), lexical (making and recognizing words) and syntactic (being able to use and recognize grammar) processes?
The challenge: talking during fMRI
One critical aspect of this research is that it is the first study to have investigated the production of sentences in detail using fMRI. Speech comprehension had already widely been studied in this manner but for speech production the problem was that too much noise was present in the measurements due to study subjects moving their mouths, facial muscles and head, and the variable quantity of air in their mouths.
This noise can't be prevented, but the researchers were able to achieve a better signal-to-noise ratio.
Says neuroscientist Laura Menenti, "In a nutshell, whereas we usually make an image with the fMRI every two seconds, we now we make five images every 2 seconds, from which we take the average for further processing."
The authors also controlled what the subjects spoke - a picture of an action — a man strangling a woman — with one person colored green and one colored red to indicate their order in the sentence. This prompted people to say either "The man is strangling the woman" or "The woman is strangled by the man."
The experiments were all carried out in Dutch, so you get some idea what Dutch researchers think about.
The results reveal a considerable overlap between brain areas (a shared 'neuronal infrastructure') which are involved in the linguistic processes associated with speech production and comprehension. Says Menenti, "Within linguistics and brain science this is a striking result. Based on studies with aphasia patients one might equally expect that speech production and comprehension would show some neuronal overlap but would otherwise each cover their own areas."
Even more striking was the fact that in their research, they did not find any results which indicated that the motor system in the brain, involved in action and movement, makes a crucial contribution to speech perception. "From the perspective of mirror neuron research that is also an unexpected result."
Citation: Laura Menenti, Sarah M. E. Gierhan, Katrien Segaert and Peter Hagoort, 'Shared Language: Overlap and Segregation of the Neuronal Infrastructure for Speaking and Listening Revealed by Functional MRI', Psychological Science, DOI: 10.1177/0956797611418347