Recovering the power of speech | Action Medical Research

Touching Lives - March 2005

Recovering the power of speech

Some people find that their speech or understanding improves spontaneously, but many more face an uphill struggle, and some never recover, even with therapy. Nobody knows why some people make progress and some people do not. There are no drugs to improve the chances of recovery, and no-one knows if current speech therapy techniques actually work, or, if they do, why.

Into the unknown

While the brain itself has been increasingly mapped over the last few years, there are many unknowns as far as the working connections between different parts of the brain are concerned.

^We’ve known for a long time that different parts of the brain do different things, but our levels of knowledge about those different parts is variable.^ One of the areas we know very little about is how the brain creates and uses language systems but this Action Medical Research project could change that.

Dr Jane Warren received a grant of over £90,000 in 2003 to study changes in speech processing in the brains of stroke sufferers. Based at Imperial College London, Dr Warren is using Positron Emission Tomography (PET) scans and Magnetic Resonance Imaging (MRI) scans to identify areas of the brain responsible for processing and understanding speech — and the findings so far are very promising.

Back to basics

Enquiring into the way the brain creates and uses language systems also means analysing the very nature and function of language itself.

Language starts by imitation. Small children repeat what they hear back to the outside world to see what reaction they get. With practise, they learn to control the production of sound, and the brain gradually learns to chop up the stream of sound it hears into meaningful chunks and combine the chunks to make sense. Conversely, the discovery of meaning allows the process to go into reverse, to convert brain impulses into sounds that make sense through talking. It’s probably the most difficult thing a human being learns, and yet most children have acquired the basic skill by the age of four or five.

^Dr Warren is studying exactly what is going on inside the brain as stroke sufferers struggle to re-establish means of communication.^ For example, the front left hand side of the temporal lobe seems to be concerned with finding meaning while the right hand side is more concerned with inflection or pitch. This side can work out who is speaking, the emotional content of what is being said and whether a question is being asked.

Australian-born Dr Warren is a passionate enthusiast for what she does. “Every stroke is different, the problems are different. The challenge is to find ways to meet each person’s individual needs.”

When a stroke occurs, the blood supply to part of the brain is blocked, and, as a result, doesn’t get any oxygen or nutrients and dies. The dead part scars over, and this can be seen in brain scans.

Brain scans can also take snapshots of how the brain is working, by measuring changes in the blood flow around the brain.When a particular area of the brain is working harder, the blood flow to that part increases, and can be measured with PET or MRI scans.These scans show, for example, which parts of the brain are working hardest when someone is listening to speech.

When an area of brain has been damaged by a stroke, the nerve cells no longer function properly, so there’s no rise in blood flow. Dr Warren is comparing what happens in healthy brains with the patterns that show up in stroke sufferers, first to get an idea of how the brain has been impaired, and then by looking at the behaviour of the patient she can understand which parts of the brain are responsible for what.

The right connections

Beyond that, with a series of snapshots over time Dr Warren can observe how the brain compensates for this dead tissue by making other parts work harder, by re-routing circuits and therefore functions and by switching from one side of the brain to the other. Though the damaged cells themselves can never be repaired, the brain has a remarkable range of alternative strategies to resume normal service.

By monitoring what the brain does during the process of repair or compensation, Dr Warren hopes to lay down a scientific framework for future therapies which can support the process, either through drugs or behavioural therapy. She describes present treatments as “just pot luck”.

Stroke often affects the rear part of the brain which links what people hear to what they say. When this part of the brain dies, one of the effects is that sufferers lose the ability to differentiate sound. They can’t monitor their speech, and so they have difficulty speaking coherently, even if the brain is sending out messages and the speaker is convinced they are making sense.This is just one of the many intense frustrations which aphasia sufferers experience.

Further findings

There are several key brain areas known to be involved in language and part of Dr Warren’s research has involved looking at how these brain areas are connected to one another and work together. Located in the left side of the brain in almost all right-handed people, areas in the temporal lobe are involved in decoding the meaning of the sounds we hear, including speech. Areas in the frontal lobes act as a sort of control centre, directing how hard other brain regions work.

Dr Warren has found that there are several circuits linking different parts of the temporal lobes with the control centres in the frontal lobes. ^Whether or not these circuits are damaged by a stroke is likely to be a big factor in determining how well a stroke sufferer recovers language function.^

As with so much in science, the more you look into it the more there is to discover, because although it’s mainly the left side of the brain that is concerned with language, there is also a thick bundle of nerve fibres that enable the left and right sides of the brain to talk to each other.

Another of the findings to come out of Dr Warren’s research so far is that this communication between the left and right sides of the brain can be affected by stroke. In fact, the better the left and right sides of the brain are cooperating, the better a stroke sufferer is able to understand spoken language after a stroke.

“This is a really exciting result”, says Jane. “It gives us something to aim for with treatments for aphasia. If we can find a way to get the left and right sides of the brain cooperating with one another better after a stroke, we could improve the chances of recovery for people who have speech comprehension problems after a stroke.”

Dr Warren is recruiting forty volunteers with no brain impairment, and twenty or more stroke sufferers. Not all stroke sufferers are able to take part in the study. She says “They mustn’t be too language-impaired, so they understand what consent is being asked of them, and can give it. There are many people who can’t tolerate the scanner, or who don’t understand what’s going on.”

In addition, they are being asked to help with the research at a time soon after they have been taken ill, and many, understandably, don’t want to make the commitment. “But the volunteers we have had have been fantastic, they’ve given endless time and trouble.”

The healthy volunteers are given a simulation of what language sounds like to stroke sufferers. Tape recordings can be distorted to the point of becoming incomprehensible, but the brain can still try and find ways of extracting meaning from the sound. Dr Warren will be looking for changes in the brain which accompany this “unscrambling” process.

^Understanding the way the brain creates and uses language systems will also have possible implications for therapies in other diseases.^

“We all have those moments when we’re lost for words,” says Jane. “And as we get older we find increasing numbers of occasions when we say, ‘It’s on the tip of my tongue…’. It’s called having a ‘senior moment’, isn’t it? What’s happening is part of a continuum which happens to all of us. At the extreme end are senile dementia and Alzheimer’s. I hope my research will help to pin down what is normal and what is abnormal.

“I think it will have huge implications for actual treatments. And that’s what I like, the combination of theory and research with hands-on clinical work which can improve people’s lives.”

Dr Warren is part of our Research Training Fellowship (RTF) scheme, which gives the country’s brightest young doctors and scientists a valuable boost to start their research careers. Action Medical Research is awarding further RTF grants later in the year — look out for a full report in Touching Lives.

Grateful thanks to Barnwood House Trust for supporting this grant.

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