The hemodynamics of oddball processing during single-tone and two-tone target detection tasks

Abstract

Event-related potential (ERP) studies have shown that the neural systems engaged during performance of oddball tasks are sensitive to contextual manipulations, such as the number of stimulus classes. Some ERP components (i.e., N1) are modulated by the number of stimulus types, while others (i.e., P3) are not greatly affected. However, little is known about how these contextual manipulations affect the hemodynamics underlying oddball processing. The purpose of this study was to examine the hemodynamic correlates of target stimulus processing in single-tone (targets alone) and two-tone (targets and standard tones) auditory oddball tasks. The primary hypothesis was that processing of salient stimuli in both contextual conditions would engage the same spatially distributed cortical and subcortical networks observed in previous oddball fMRI studies. Results were consistent with this hypothesis and suggest that the brain engages many potentially useful brain regions during salient stimulus processing despite the low probability that said regions are necessary for task performance, which likely reflects a form of "adaptive reflexive processing". Results were also consistent with ERP data that shows that the N1 is larger for single-tone tasks by showing greater amplitude of hemodynamic response for single-tone targets, relative to two-tone targets, in bilateral temporal cortex and bilateral inferior lateral frontal cortex. The results are discussed as they relate to the understanding of neurocognitive function pertaining to contextual manipulations in general, and orienting processes in particular.

Figure 1

Illustration of the hemodynamic response elicited by target detection in the single-tone task. The results are thresholded at False Discovery Rate of q <.0001, corrected for multiple comparisons. The view is in neurological convention (i.e., left hemisphere is on the left).

Figure 2

Illustration of the hemodynamic response elicited by target detection in the two-tone task. The results are thresholded at False Discovery Rate of q <.0001, corrected for multiple comparisons). The view is in neurological convention (i.e., left hemisphere is on the left).

Figure 3

Illustration of the regions in which the amplitude of the hemodynamic response was larger for target detection in the single-tone task than in the two-tone task. The results are thresholded at a False Discovery rate of q <.05, corrected for multiple comparisons). The view is in neurological convention (i.e., left hemisphere is on the left).

Figure 4

Fitted hemodynamic response estimates averaged across sessions and subjects for single- and two-tone target stimuli for selected regions in prefrontal cortex, parietal lobe, basal ganglia, and cerebellum regions. Single-tone (blue) reflects target hemodynamic response amplitude relative to the implicit baseline. Two-tone (red) reflects target hemodynamic response amplitude relative to frequent nontargets.