Academic journal article Cognitive, Affective and Behavioral Neuroscience

Selective Tuning of the Right Inferior Frontal Gyrus during Target Detection

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Selective Tuning of the Right Inferior Frontal Gyrus during Target Detection

Article excerpt

In the human brain, a network of frontal and parietal regions is commonly recruited during tasks that demand the deliberate, focused control of thought and action. Previously, using a simple target detection task, we reported striking differences in the selectivity of the BOLD response in anatomically distinct subregions of this network. In particular, it was observed that the right inferior frontal gyrus (IFG) followed a tightly tuned function, selectively responding only to the current target object. Here, we examine this functional specialization further, using adapted versions of our original task. Our results demonstrate that the response of the right IFG to targets is a strong and replicable phenomenon. It occurs under increased attentional load, when targets and distractors are equally frequent, and when controlling for inhibitory processes. These findings support the hypothesis that the right IFG responds selectively to those items that are of the most relevance to the currently intended task schema.

In a recent article, we used event-related fMRI to compare the neural responses in distinct subregions of the frontal and parietal cortices during a simple target detection task (Hampshire, Duncan, & Owen, 2007). Participants were initially presented with a target object: a face, building, abstract shape, or line figure. Subsequently, they monitored sequences of distractor objects for occasional presentation of the target. We reported striking differences in selectivity of the BOLD response in different frontoparietal regions. Whereas the more ventral and posterior extent of the lateral prefrontal cortex (inferior frontal gyrus, or IFG) responded selectively only to the current target object, more dorsal and anterior portions (middle frontal gyrus, or MFG) and the inferior parietal cortex (IPC) were more active during the presentation of both targets and distractors from the same category as the target. A lateralization effect was also evident, favoring heightened BOLD response to targets in the right hemisphere. Our results suggested that within the frontoparietal cortex, the right IFG responds particularly selectively when the attended input matches the current focus of intended action (Owen & Hampshire, in press).

More broadly, evidence from a range of sources has suggested that there is an adaptable global system for working memory and attention, distributed across a network of frontal and parietal brain regions. This global attentional network appears to underlie the flexibility of human behavior by enabling us to deliberately and selectively focus our attention on currently relevant information (Duncan, 2001, 2006; Miller & Cohen, 2001). In support of this hypothesis, it has been reported that, within the human brain, a consistent set of frontal and parietal regions is commonly recruited under a broad range of cognitive demands (Braver, Reynolds, & Donaldson, 2003; D'Esposito, Postle, Ballard, & Lease, 1999; Dove, Pollmann, Schubert, Wiggins, & von Cramon, 2000; Dreher, Koechlin, Ali, & Grafman, 2002; Hampshire & Owen, 2006; Kimberg, Aguirre, & D'Esposito, 2000; Sohn, Ursu, Anderson, Stenger, & Carter, 2000). Research using single unit recording also supports this hypothesis, with neurons within the monkey lateral prefrontal cortex rapidly adapting to respond to a broad range of task-relevant information yet becoming unresponsive to that same information when the task demands change (Everling, Tinsley, Gaffan, & Duncan, 2002; Freedman, Riesenhuber, Poggio, & Miller, 2001; Miller & Cohen, 2001).

Although the existence of a frontoparietal network for coding of task-relevant information is now widely accepted, the contributions made by the anatomically distinct subregions of this network remain controversial. Of particular relevance to the present study are several influential models that propose that the lateral prefrontal cortex is functionally organized along an inferior- superior (or ventral-dorsal) axis. …

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