What Is That Word ... ?
Ever been frustrated because the word you’re looking for is eluding you?
Most of us forgive ourselves the occasional forgetfulness, but for stroke patients suffering from aphasia, the inability to find the right word can be frequent and profound. Tatiana Schnur wants to know why.
When speaking, a person must select one word from a competing set of words. A speaker who wants to mention a specific animal, for example, has to single out “dog” from “cat,” “horse” and other similar possibilities. Schnur, an assistant professor of psychology, wondered whether a particular part of the brain is necessary for resolving the competition for choosing the correct word.
She and her colleagues compared brain images from 16 healthy volunteers and 12 volunteers who suffer from aphasia, a language disorder acquired as a result of stroke. People who have aphasia frequently experience difficulty with speech. The study covered two experiments where people named a series of images and conflict between words increased as more images were named. In the first experiment, healthy speakers’ brain activations were measured using functional magnetic resonance imaging. The second experiment mapped performance deficits to lesion locations in participants with aphasia.
The researchers found that while two parts of the brain — the left inferior frontal gyrus (LIFG) and the left temporal cortex — respond to increased conflict among words competing for selection during speech, only the LIFG is necessary to resolve the competition for successful word production. The LIFG includes Broca’s area, which is responsible for aspects of speech production, language processing and language comprehension. It is of particular interest to the researchers because damage to this area may explain the hesitant, nonfluent speech exhibited by those described as Broca’s aphasics.
By looking at direct parallels between the healthy and aphasic volunteers, Schnur and colleagues coupled location in the brain with specific speech processes, and they learned that the ability of aphasic speakers to resolve competition that arises in the course of language processing does appear to depend on the integrity of the LIFG.
The study, “Localizing interference during naming: Convergent neuroimaging and neuropsychological evidence for the function of Broca’s area,” was published in the Proceedings of the National Academy of Sciences. It was funded by the National Institutes of Health.