Study maps new brain regions behind intended speech

Scientists have, for the first time, identified brain regions outside the frontal lobe involved in the intent to produce speech. The research, published in the Journal of Neural Engineering, could pave the way for using technology known as a brain computer interface (BCI) to manage Broca’s aphasia.

Broca’s aphasia is a language disorder that affects the ability to speak or write. It can be caused by damage to the frontal lobe, leaving  patients unable to say what they intend to say.  While the current go-to treatment is speech therapy, scientists at Northwestern University aim to use a BCI to convert brain signals into spoken words. The first step in this process is determining where in the brain the BCI should record from to decode someone’s intended speech.

Currently, BCI devices are only used on individuals with paralysis from amyotrophic lateral sclerosis (ALS) or stroke in the brainstem, which leaves them unable to move or communicate.

In these patients, BCIs record signals from the frontal lobe. But Broca’s aphasia, which most often affects people after a stroke or brain tumour, results from damage to the frontal lobe of the brain, where speech production and parts of language are processed. So, to help patients with Broca’s aphasia, scientists would likely need to record signals from other areas of the brain.

In the new study, Northwestern Medicine scientists have, for the first time, identified specific brain regions outside the frontal lobe — in the temporal and parietal cortices — involved in the intent to produce speech. This opens the door to using a BCI to treat Broca’s aphasia.

‘This is a small, but necessary step,’ said Dr Marc Slutzky, professor of neurology and neuroscience at Northwestern University Feinberg School of Medicine. ‘We showed that these non-frontal areas indeed contain information about someone’s intent to produce speech that allowed us to distinguish when they were going to speak versus when they’re not speaking or are just thinking about something that they don’t want to say out loud.’

These early findings will help scientists when they eventually design a BCI for patients with Broca’s aphasia to distinguish whether someone’s speech-related information is related to language production or language perception (including comprehension).

While the goal is ultimately to work with patients with aphasia, this study was in patients who did not have language deficits. The scientists recorded electrical signals from the surface of the cortex in nine patients with either epilepsy or brain tumours. The electrode arrays were either implanted in people with epilepsy as part of their seizure monitoring prior to surgery or placed on the brain temporarily in the operating room, while patients with tumours underwent awake brain surgery and mapping.
Then, patients either read words aloud from a monitor or were silent (at rest) while investigators recorded their brain signals (called electrocorticography or ECoG). The next step in this research will be to decode what these patients actually said.

‘It is critical to not be decoding the user’s thoughts that are not intended to be spoken aloud, both for that practical reason and for the ethical problems this could incur,’ Dr Slutzky said.