Time Course Evaluations
The time course data demonstrate the transient changes produced by single incongruent events (Fig 3). The temporally dispersed activation of areas represent differences produced by incongruent and congruent stimuli in perception of visual stimuli (word and color), word–color form interpretation, selective attention, selection of response, and generation of response (color naming/word reading). Since we obtain images by measuring differences in activation between congruent and incongruent stimulus trials, we do not expect significant additional activation in the primary effects of visual excitation and form perception, in primary motor effects of word generation, or from differences in automatic responses such as word reading. The activation maps should thus reflect changes of brain activation across time related to the selection of the stimulus, the execution of the appropriate response, the monitoring of task performance, and the suppression of inappropriate responses (error correction). Our data demonstrate differential time course patterns between the ACG and frontal activations.
The event-related Stroop results show that different activated regions can be dissociated temporally. The differential onset and offset of activation supports the idea that differential information processing occurs in distributed brain regions in the Stroop task. Potentially, the temporal information from event-related fMRI studies can help us learn more about the differential timing of regional brain activations during a cognitive task, although the physiological basis for different timings remains unclear. For example, patterns of temporal activity may be used to assess the temporal relationships between regions and to provide information on functional connectivity among brain regions. Preliminary results using such data with a larger sample of subjects will be presented in a subsequent report.
Comparison with the Oddball Effect