Publications from 2005

Bitan T, Booth JR, Choy J, Burman DD, Gitelman DR & Mesulam MM (2005) Shifts of effective connectivity within a language network during rhyming and spelling. Journal of Neuroscience, 25, 5397-5403. [pdf]

We used fMRI to examine task-specific modulations of effective connectivity within a left hemisphere language network during spelling and rhyming judgments on visually presented words. We identified sites showing task specific activations for rhyming in the lateral temporal cortex (LTC), and for spelling in the intraparietal sulcus (IPS). The inferior frontal (IFG) and fusiform gyri (FG) were engaged by both tasks. Dynamic causal modeling showed that each task preferentially strengthened modulatory influences converging upon its task specific site (LTC for rhyming, IPS for spelling). These remarkably selective and symmetrical findings demonstrate that the nature of the behavioral task dynamically shifts the locus of integration (or convergence) to the network component specialized for that task. Furthermore, they suggest that the role of the task-selective areas is to provide a differential synthesis of incoming information rather than providing differential control signals influencing the activity of other network components. Our findings also showed that switching tasks led to changes in the target area influenced by the IFG, suggesting that the IFG may play a pivotal role in setting the cognitive context for each task. We propose that task-dependent shifts in effective connectivity are likely to be mediated through top-down modulations from the IFG to the task-selective regions, in a way that differentially enhances their sensitivity to incoming word-form information.

Booth JR & Burman DD (2005). Using neuro-imaging to test developmental models of reading acquisition. In H Catts & A Kamhi (Eds), The Connections Between Language and Reading Disabilities. Lawrence Erlbaum Associates: Mahwah, NJ. [pdf]

This chapter presented a series of experiments that examined developmental differences in the neuro-cognitive network for lexical processing in either the visual or auditory modality. The lexical tasks involved spelling, rhyming or meaning judgments that tapped into orthographic, phonological and semantic representations. In general, our research suggests that there is a developmental shift from an early reliance on semantics to a later reliance on orthographic and phonologic representations for rapid word recognition. The first main finding was that children, but not adults, showed activation in the middle temporal gyrus during the spelling and rhyming tasks in both modalities. Because previous research has implicated this region in meaning-based processing, our results suggest a greater reliance on semantics in children during lexical processing. The second main finding was that adults, but not children, showed activation in the fusiform gyrus during the auditory tasks. Because the fusiform gyrus has been implicated in orthographic processing, our results suggest greater interactive processing between phonology and orthography for the adults. The third main finding was that adults, but not children, showed greater activation during the cross-modal as compared to the intra-modal lexical tasks in the neuro-cognitive networks involved in mapping between orthographic and phonological representations. The visual rhyming task, which required conversion from orthography to phonology, produced activation for adults in the supramarginal/angular gyrus and in the superior temporal gyrus. The auditory spelling task, which required conversion from phonology to orthography, produced activation for adults in the supramarginal/angular gyrus and in the fusiform gyrus. These developmental results are consistent with developmental models of reading and spelling that postulate single- rather than dual-routes for converting between representational systems. Our research shows how behavioral and brain activation measures can be used in conjunction to test developmental models of reading acquisition.

Booth JR, Burman DD, Meyer JR, Zhang L, Trommer B, Davenport N, Li W, Parrish TR, Gitelman DR & Mesulam MM (2005). Larger deficits in brain networks for response inhibition than for visual selective attention in attention deficit hyperactivity disorder (ADHD). Journal of Child Psychology and Psychiatry, 46, 94-111. [pdf]

Brain activation differences between 12 control and 12 attention deficit hyperactivity disorder (ADHD) children (9 to 12-year-olds) were examined on two cognitive tasks during functional magnetic resonance imaging (fMRI). Visual selective attention was measured with the visual search of a conjunction target (red triangle) in a field of distracters and response inhibition was measured with a go no-go task. There were limited group differences in the selective attention task with control children showing significantly greater intensity of activation in a small area of the superior parietal lobule region of interest. There were large group differences in the response inhibition task with control children showing significantly greater intensity of activation in fronto-striatal regions of interest including the inferior, middle, superior and medial frontal gyri as well as the caudate nucleus and globus pallidus. The widespread hypoactivity for the ADHD children on the go no-go task is consistent with the hypothesis that response inhibition is a central deficit in attention deficit hyperactivity disorder.