Exploring Cortical Attentional System by Using fMRI during a Continuous Perfomance Test

Functional magnetic resonance imaging (fMRI) was performed in eight healthy subjects to identify the localization, magnitude, and volume extent of activation in brain regions that are involved in blood oxygen level-dependent (BOLD) response during the performance of Conners' Continuous Performance Test (CPT). An extensive brain network was activated during the task including frontal, temporal, and occipital cortical areas and left cerebellum. The more activated cluster in terms of volume extent and magnitude was located in the right anterior cingulate cortex (ACC). Analyzing the dynamic trend of the activation in the identified areas during the entire duration of the sustained attention test, we found a progressive decreasing of BOLD response probably due to a habituation effect without any deterioration of the performances. The observed brain network is consistent with existing models of visual object processing and attentional control and may serve as a basis for fMRI studies in clinical populations with neuropsychological deficits in Conners' CPT performance. 1. Introduction Sustained attention is defined as the ability to maintain a high vigilance level for a long time, allowing the subject to respond against presentation of infrequent and unpredictable events. One of the most widely used neuropsychological tests for the study of sustained attention is the Conners' Continuous Performance Test (CPT) [1]. The Conners’ CPT is derived from the original CPT of Rosvold [2], which was developed to assess vigilance. In the Rosvold CPT, the stimuli are letters which are presented visually one at a time, at a fixed rate and the subject's task is to respond whenever the letter representing the target stimulus appears and to inhibit a response when any other letter appears. The letter chosen as target stimulus is typically X and the Rosenov test is therefore, also known as the “X-CPT.” Several neuropsychological tests are derived from the X-CPT and the fundamental paradigm on which all these are based is the serial presentation of target and nontarget stimuli and the subject's task is to respond or inhibit response to infrequent visual target stimuli. In Conners' CPT, also known as “not-X-CPT”, the target stimuli are the letters X like in the Rosvold’s test, but the subject’s task is to respond to nontarget stimuli and to inhibit response to target stimuli [3]. Although the Conners CPT is designed to evaluate attention; it has been shown that task performance relies on diverse motor, sensory, and cognitive functions (e.g., maintenance of task instructions,