Monday, March 22, 2010
Accessibility Level: Intermediate/Advanced
Today we’re again looking at the theme of increasing specialization in the brain over development. Rather than specialization in terms of spatial extent, as touched on in Brown 2004, Cerebral Cortex, this paper’s finding suggests specialization in processing of sensory modalities.
Church and colleagues tested children (age 7-10) and adults (18-35) in a word generation task. During the experiment they read words off a screen and repeated words presented aurally. Like the two papers previously discussed here by this group, the authors matched for behavior between children and adults.
They authors report several findings.
1. First, most brain regions did not change in activation over time. In well known language areas like the inferior frontal gyrus and superior temporal gyrus, the authors found no difference between children and adults. Also, they found no differences in lateralization (how much one side of the brain was favored over another) between children and adults.
2. The regions that differed between the two groups were mainly extrastriate visual regions, and all regions with differences had greater activation for children than adults. Unlike the Brown 2005 paper, where some frontal regions were found to have greater activation in adults, this paper found no such regions. This could be due to the different task (word generation vs. reading/repeating), or variation in the participant pools of the two the studies.
3. In several visual regions, including a cluster very close to the visual word form area, adults had more activation to the visual presentation than to auditory presentation, while children had similar activation to the two modalities. This suggests that these areas might be more specialized for the visual modality in adults. In other words, the region gets “tuned” to the visual modality as the children mature (However, the interaction between modality and age was not statistically significant). The authors propose several possible mechanisms responsible for this modality tuning difference. Perhaps the kids are using a different strategy, visualizing more during the auditory task. Or perhaps their brains are just organized differently.
Together with the Brown 2004 paper, this paper presents an interesting story about increasing specialization and efficiency in the maturing brain, in which the immature brain starts out with relatively nonspecialized brain regions and recruits more brain regions to accomplish the tasks at hand. Then, maturation and expertise result in more specialization, finer tuning, and fewer recruited regions.
Church JA, Coalson RS, Lugar HM, Petersen SE, & Schlaggar BL (2008). A developmental fMRI study of reading and repetition reveals changes in phonological and visual mechanisms over age. Cerebral cortex (New York, N.Y. : 1991), 18 (9), 2054-65 PMID: 18245043