New study reveals complex speech networks in the brain

Scientists at Imperial College London have succeeded in untangling some of the complex neural pathways in our brain that enable us to speak.

The findings, published in the Journal of Neuroscience, improve scientists’ understanding of how speech is organised in the brain. The disruption to these pathways may help explain difficulties in patients with stroke who have impaired speech and it is hoped that this knowledge could in the future lead to improved treatments.

Each year, more than 150,000 people in the UK suffer a stroke, which occurs when part of the blood supply to the brain is cut off through a blood vessel blockage or a bleed in the brain. Around a third of stroke patients will be left with problems with speech and language, known as aphasia.

Using MRI scanning techniques, researchers examined a cohort of 24 healthy volunteers to identify activity in different brain networks when a person is speaking and examine how these networks work together to enable speech.

The study isolated particular networks primarily responsible for speech, but also identified other, overlapping general brain networks which are activated or suppressed during the speech process. By examining how these networks are organised in the healthy brain, the researchers believe they can have a better understanding of how they are damaged in stroke patients who have difficulty in talking and ultimately improve the function of these networks – through drugs or therapy – to help the patient improve their speech.

Dr Fatemeh Geranmayeh, a Wellcome Trust Clinical Research Fellow from the Department of Medicine at Imperial, who led the study, explained: “To be able to help stroke patients with aphasia, we first need a clearer understanding of how speech is organised in the healthy brain. We know that speech results from a complex series of events: we first have to formulate a message in our minds; access our repertoire of words to convey a meaning; put these words into the correct order, and then articulate them. At the same time, we have to pay attention to what we are saying, monitor speech errors, and modulate what we say depending on how the message is being perceived.

“All these are done through a number of widely distributed and complex brain networks, that simultaneously mediate speech function and other general cognitive brain functions, some of which activate whilst others are suppressed, in order to carry out the task of speaking. To further complicate the picture, these networks interlock and overlap in certain areas of the brain making them difficult to detect."

A cohort of patients with stroke-related speech problems has already been recruited to the next phase of the study that aims to investigate the disruption of these networks in patients. It is hoped that, ultimately, the research will lead to improvements in therapies for people with language disorders, particularly as a result of a stroke.

“It seems likely that successful rehabilitative therapies should aim to improve not only the networks that are directly responsible for speech function, but also in other more general cognitive brain networks,” added Dr Geranmayeh.

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Reference: ‘Overlapping Networks Engaged during Spoken Language Production and its Cognitive Control’, Journal of Neuroscience, Fatemeh Geranmayeh, Richard J.S. Wise,  Amrish Mehta, and Robert Leech, . This is a free access article, available at: http://www.jneurosci.org/content/34/26/8728.abstract?etoc