Four-legged ducks help decipher brain function
September 2006
A team in the School of Psychological Sciences led by Professor Matt Lambon Ralph has identified the part of the brain that forms and processes concepts.
Professor Lambon Ralph’s recent British Association for the Advancement of Science’s Charles Darwin Award Lecture, ‘Investigations of concepts and meaning: the case of the four-legged duck’, described how his team used brain scans and neuropsychological investigations from people suffering from semantic dementia to discover that the brain’s temporal pole seems to be critical in encoding concepts and storing meaning.
Although patients with damage to this area are able to carry out other aspects of forms of higher mental activity, they gradually lose the knowledge that underpins concepts.
Four-legged duck
This can be seen in a variety of different verbal and non-verbal tasks: one patient for example was only able to draw an accurate picture of a duck when shown a photograph of one, and sketched a hybrid, four-legged creature within a minute of it being removed.
“It’s not that these patients know what a duck is one minute and don’t the next,” Professor Lambon Ralph said, “but to reproduce a picture at a later time we need to use our conceptual knowledge. In this case, the underlying concepts of birds and animals had become so fuzzy that they had become confused. Patients at this stage also make similar mistakes when naming birds, calling them ‘cat’ or ‘dog’.”
Slower brain activity
By artificially slowing down the temporal pole’s activities in volunteers with normal brains, using a technique called transcranial magnetic stimulation (TMS) which uses magnetic pulses to temporarily exhaust the temporal pole, the team demonstrated a slowing-down of about 10% when people were asked to make judgements of meaning. “This really reinforced the idea that the temporal lobe is where these concepts are encoded,” Professor Lambon Ralph said. “The process had previously thought to be linked to an area further back in the temporal lobe.”
The team is now working with therapists to see if a form of speech training for patients could help counter temporal lobe damage.
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