Weaker top-down modulation from the left inferior frontal gyrus in children

Abstract

Previous studies have shown that developmental changes in the structure and function of prefrontal regions can continue throughout childhood and adolescence. Our recent results suggested a role for the left inferior frontal cortex in modulating task-dependent shifts in effective connectivity when adults focus on orthographic versus phonological aspects of presented words. Specifically, the top-down influence of the inferior frontal cortex determined whether incoming word-form information from the fusiform gyrus would have a greater impact on the parietal areas involved in orthographic processing or temporal areas involved in phonological processing (Bitan, T., Booth, J.R., Choy, J., Burman, D.D., Gitelman, D.R. and Mesulam, M.-M., 2005. Shifts of Effective Connectivity within a Language Network during Rhyming and Spelling. J. Neurosci. 25, 5397-5403.). In the current study, we find that children displayed an identical pattern of task-dependent functional activations within this network. In comparison to adults, however, children had significantly weaker top-down modulatory influences emanating from the inferior frontal area. Adult language processing may thus involve greater top-down cognitive control compared to children, resulting in less interference from task-irrelevant information.

Fig. 1

Regions included in the effective connectivity analysis. (A) Group activation for the spelling and rhyming tasks compared to their mean. FG—fusiform gyrus, LTC—lateral temporal cortex, IFG—inferior frontal gyrus, IPS—intraparietal sulcus. (B) Centers of ROIs in individual subjects. Purple—IFG, Orange—FG, Yellow—LTC, Blue—IPS.

Fig. 2

Modulatory effects of the tasks. Effects of the spelling and rhyming tasks in children (A, B respectively) and in adults (C, D respectively) are presented. The average effects across individuals are displayed, with significant effects in black, and non-significant effect in grey. Pairs of effects that are significantly different are indicated by * (and connected by a dotted arc in distant pairs) with the stronger effect indicated in bold. For example, in panel A, the dotted arc on the right indicates that the fusiform area had a significantly greater influence on the IPS than on the LTC in the spelling task.

Fig. 3

Modulatory effects that are stronger in adults compared to children.