By studying patients suffering from semantic dementia and by carrying out transient impairment of healthy individuals, Professor Lambon-Ralph of the University of Manchester has located a specific part of the brain involved in retaining meanings and revealed the huge impact on the lives of individuals for whom this goes wrong.
While most of us take our ability to understand the world around us for granted, others are not so lucky. Some people who have suffered brain damage in a specific part of their brain, be it from stroke, dementia, infection or head injury, suffer from a breakdown in the storage of meanings. This leads to major disabilities and a compromised ability to work, play and communicate.
“Conceptual knowledge or semantic memory refers to our store of meanings for words, objects, people and so on. It is the way our brain gives meaning to all the sensory experience in our lives. It is also at the heart of communication and language,” Professor Lambon-Ralph explains.
“We have used multiple, intersecting methods to answer the question of how the brain comes to store meanings and concepts. These include the study of patients with a particular type of dementia, brain imaging methods and transcranial magnetic stimulation (TMS) – a technique that uses a magnetic coil to ‘tire-out’ a small area of the brain.”
Professor Lambon-Ralph will present his findings as part of the BA Charles Darwin Award Lecture – ‘The case of the four-legged duck: investigations of concepts and meaning’ at the BA Festival of Science – taking place in Norwich from 2-9 September and bringing together over 300 of the UK’s top scientists and engineers to discuss the latest scientific developments with the public.
Patients with semantic dementia suffer gradual loss of tissue from part of the brain known as the anterior temporal lobe, resulting in a progressive breakdown of concepts. “Concepts are not deleted as whole entities but, instead, they gradually degrade,” says Professor Lambon-Ralph. “This means that similar concepts become increasingly difficult for the patients to tell apart and they begin to confuse one concept with another.”
“Patients show this pattern, irrespective of which type of input is probed – thus they show poor understanding of spoken words, written words, pictures, smells, sounds and touch. This indicates that our meanings are stored in abstract form and serve all the different forms of verbal and sensory input. The same problems are exhibited when the patients try to express this knowledge – they substitute a related name (for example “duck” becomes “chicken” or “cat”) and sometimes produce striking drawings in which concepts seem to merge together, mixing up information about birds and animals to produce four-legged ducks.”
Using a special form of brain imaging, Professor Lambon-Ralph has shown that the temporal lobe damaged in dementia patients is widely connected to the rest of the brain.
“We have used computer/mathematical models to mimic the functioning of this area and its brain connections, and thus show how concepts are formed. It does this by bringing together information from all the different senses and distilling this into a unified store,” he explains.
By using TMS to temporarily fatigue the temporal lobe of healthy patients, Professor Lambon-Ralph has been able to mimic the symptoms of semantic dementia patients. Although the effects are not as marked as in sufferers, it has allowed him to isolate a key location of concept storage in the brain.
The opportunity to present a popular and prestigious BA award lecture at the Festival of Science is offered to five outstanding communicators each year. The award lectures aim to promote open and informed discussion on issues involving science and actively encourage young scientists to explore the social aspects of their research, providing them with reward and recognition for doing so.
In addition to lectures and debates at the University of East Anglia, the Festival will also feature a host of events throughout Norwich as part of the Science in the City programme.
This year’s Festival is supported by the University of East Anglia, the East of England Development Agency and Microsoft Research. The Press Centre is sponsored by AstraZeneca.
Lisa Hendry | alfa
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