The Neural Cascade of Attentional Control

0004 In our complex and multifaceted world, our senses are continuously bombarded with much more information than our brains can fully process. Attention is a critical cognitive function that allows us to select for detailed analysis only the most relevant information at any given moment. The crucial nature of attention is clearly evident in the game “Where’s Waldo.” Picking out the odd, bespectacled man wearing the familiar red-and-white striped shirt and hat amidst an array of distracting objects that contain similar colors and patterns is astonishingly diffi cult. Only by directing our attention or our eyes sequentially to many different spatial locations can we eventually fi nd Waldo. However, the basic neural mechanisms that allow us to focus our attention on specifi c locations in our visual fi eld, even in uncluttered scenes, are not well understood. Previous functional neuroimaging studies have revealed a network of frontal and parietal brain regions that, along with the visual cortex, show enhanced activity during visual-spatial attention. It has been hypothesized that this frontal-parietal network controls attention by sending “top-down” signals that “bias” activity in specifi c regions of visual cortex. This biasing activity is, in turn, thought to facilitate the accurate, rapid processing of information in attended regions of space. However, these neuroimaging studies were unable to elucidate the temporal cascade of neural events associated with the control of attention—critical information for understanding how different brain regions coordinate their actions as succeeding stages of attentional control unfold. In this study, Tineke Grent-‘t-Jong and Marty Woldorff set out to discover both the timing and location of brain activations in the attentional control network that underlie our ability to direct our visual spatial attention. To do this, the authors combined two complementary methods: event-related potentials (ERPs), which measure electrical changes in the brain with scalp electrodes and thus provide very precise timing information on brain activity triggered by sensory or cognitive events, and functional magnetic resonance imaging (fMRI), which localizes event-triggered brain activations by measuring associated changes in blood fl ow. This innovative study surmounted previous obstacles to the study of attentional control by including important control conditions and by using the exact same experimental paradigm and task contrasts (comparisons of patterns of activation elicited by different tasks) for both methodologies. This multimethodological approach enabled the authors to obtain measures of cognitive brain activity with good temporal and spatial resolution and thereby gain a more complete understanding of the neural mechanisms underlying topdown attentional control. The authors used a spatial cueing paradigm in which participants kept their visual gaze directed toward the center of a computer screen. A series of 4-second trials were presented, with an instructional letter cue displayed at the beginning of each trial. On most trials, the letter cue (“L” or “R”) instructed them to covertly attend (that is, without moving their eyes) to either the lower left or the lower right portion of the screen to try to detect the possible brief appearance of a faint dot at the cued location. However, the authors included an important control condition: on some trials, the cue (“P”) instructed the subject to not orient their attention to a particular location, as no faint dot would appear during that trial. By incorporating both of these interpret-cue trials and attention-orienting trials, Grent-‘t-Jong and Woldorff were able to separate the activations related to spatial orienting from those associated with general cue processing that were not related to orienting. Both the ERP and fMRI results revealed that some activations were elicited by both the interpret cues and the attentional-orienting cues, and some were associated only with attentional orienting. More specifi cally, the ERPs showed that during the fi rst 400 ms, the attend-cue and interpretcue trials produced similar patterns of activity, which the fMRI indicated was associated with the more lateral regions of frontal and parietal cortex. After 400 ms, the response to the interpret cues quickly returned to baseline, whereas the attend cues elicited additional, widespread waves of orientingspecifi c activity that continued for hundreds of milliseconds. Moreover, the fMRI confi rmed that this orienting-related activity was associated with greater activation specifi cally in the more medial portions of the frontal and parietal cortex. These results indicate that lateral parts of the frontal-parietal network play a role in the initial general cue processing and interpretation, whereas the more medial frontal-parietal regions function more specifi cally in the subsequent orienting of spatial attention. The authors then set out to determine the relative timing of the medial frontal and parietal activations underlying this attentional-orienting process. To do this, the authors used modeling procedures to relate these orienting-specifi c regions delineated by the fMRI to the corresponding The Neural Cascade of Attentional Control