THE ROLE OF ATTENTION IN COGNITIVE DISABILITIES Marie T. Banich Dept. of Psychology, University of Colorado at Boulder Dept. of Psychiatry, University of Colorado Health Sciences Center To examine this issue further, we performed another study (Milham et al, in press b). We reasoned that if this area is specific to response selection, it should only be active when the word provides conflicting information about a response, but should be impervious to conflict at other levels, such as meaning. Furthermore, it should exhibit no difference in activity between neutral words and incongruent color words that don’t name a possible response (called incongruent response ineligible trials). Introduction What is attention? The focus of our laboratory is to utilize modern brain-imaging techniques to understand the neural systems that control attention. Although there is no single generally agreed upon definition of attention, all models invoke the idea of selection. Since the brain receives and must process much more information than it can handle at one time, there must be a way to select the information that is critical for task performance. This selection can occur at multiple stages of processing - with regards to incoming sensory information, with regards to information that must be “kept in mind”, and with regards to the possible responses. The ability to control attention is a basic process that must occur for any mental function to occur successfully. For example, recognizing an object requires selecting the relevant visual features while disregarding others, remembering a story requires selecting the critical themes and disregarding extraneous details, and so forth. The role of attention in cognitive disability Given its central role in most mental functions, it is not surprising that attentional problems are commonly observed in learning disabilities and occur as a consequence of brain injury. The importance of attentional function for cognitive disabilities is broad-ranging. In addition to being the cardinal symptom of attention deficit disorder, attentional problems occur in various types of dementia (e. g. , Morris, 1996) including the early stages of Alzheimer’s disease (e. g. , Baddeley, Bucks, & Wilcock, 2001), and are a common consequence of stroke, predicting the degree of subsequent recovery (e. g. , Paolucci et al, 2001). Attentional problems are also one of the major consequences of head injury (Cossa & Fabiani, 1999), lingering even in the case of mild head injury (e. g. , Potter, Bassett, Jory & Barrett, 2001). Rehabilitation programs for brain injury involve addressing attentional difficulties (Cicerone et al, 2000), which have been posited to be a key roadblock to independent functioning and reintegration into the community (e. g. , Chan, 2001). How is attention controlled by the brain? Given that attention is affected in a large variety of cognitive disabilities, it is not surprising that it is controlled by a network of brain structures. Hence, damage to any component can degrade performance. The brain regions typically implicated in attentional control include regions of the prefrontal cortex, the anterior cingulate, parietal regions, and sensory regions that process task-related information. These regions are shown below. Identify the ink color: Response conflict Incongruent>Neutral Color-word Spatial-word Both Dorsolateral cortex becomes active regardless of what type of information is taskrelevant In another study, we found that dorsolateral prefrontal cortex is only active when it is hard to impose an attentional set (Banich et al, 2000 b). In this study we compared performance on a color-word and color-object task. Once again we compared incongruent to neutral trials. In this study, we either had individuals pay attention to the color or the item (the word or the object). In the color-word task, it is easy to pay attention to the word, since we read relatively automatically, as compared to the color. However, the relationship is opposite in the color-object task, it is easier to pay attention to the color than the object. Color-Word Stimuli N eu tra l Color-Object Stimuli In co n gr ue nt DOOR N eutra l In co ngr ue nt B L UE Inferior prefrontal cortex Incongruent Eligible RED = Incongruent Ineligible In this study we wanted to see the timing relationships of brain regions that become active as one learns to impose attentional control (Milham et al, submitted). To do so we taught people to 100% accuracy to learn to associate a color name with a nonsense shape. “green” Attend to item (word)-EASY Attend to item (object)-HARD Incongruent>Neutral Color-Word Attend to: Color-Object Color Easy Hard We examined performance over a series of trials, dividing the session into thirds. Below is shown how well activity for cingulate and associated regions (above) and dorsolateral regions (below) is associated with greater activity on incongruent than neutral trials. 1 st third 2 nd third Item Hard Our Prior Findings A. Creating an attentional “set”: The role of the dorsolateral prefrontal cortex We have found that the dorsolateral prefrontal cortex is critical for the ability to create an attentional set - that is the ability to keep in mind what is task-relevant while ignoring that which is task-irrelevant. Such an attentional set is necessary when taskirrelevant information is distracting. A number of our studies support this assertion. First, we found that this region becomes active whenever it is hard to pay attention, regardless of what you need to pay attention to - an item’s color, its spatial relationship, and so forth. In one study, we compared variants of the Stroop task, a color-word task and a spatial-word Stroop task (Banich et al. , 2000 a). We vary attentional demands so that in the more demanding condition, the distracting information, the word, conflicts with the task-relevant information (e. g, . color or spatial relationship), while in the easier condition, it is does not. “blue” After training, we examined their response to either incongruent or neutral trials. Attend to color-EASY Easy How do we examine attention? To examine attentional control, we utilize variants of a simple but powerful task that has been referred to as the “gold standard” of attentional control, the Stroop task. In this task, individuals must pay attention to one element of the stimulus, the task-relevant dimension (e. g. color), while ignoring another dimension of the stimulus, the task-irrelevant dimension (e. g. , shape). To examine brain activity during performance of these tasks, we use functional magnetic resonance imaging (in collaboration with the Depts. of Radiology and Psychiatry at University of Colorado Health Sciences Center). Neutral C. The temporal relationship between brain regions as one learns to impose atentional control. One of the major issues of scientific debate in the field currently is exactly what roles each of these regions play in attentional control. In our laboratory, we have focused on disentangling the roles of these different regions, so that we can understand the precise way in which the brain controls attention. LOT The anterior cingulate showed the expected pattern - responding when the word names a conflicting response, but not when it does not. “yellow” Attend to color-HARD Posterior sensory cortex Anterior cingulate cortex > BLUE Eligible > Ineligible = Neutral Parietal cortex Dorsolateral prefrontal cortex No response conflict Dorsolateral prefrontal cortex becomes active when it is important to impose an attentional set, but is not activated when a process can be done relatively automatically. B. Selecting a correct response: Role of the anterior cingulate We have performed a number of studies that indicate that the anterior cingulate, in particular the posterior dorsal segment, is responsible for selecting the response that an individual makes. First, the cingulate is active when the word in the color-word Stroop task names a conflicting response, but not when the word names a congruent response or has no response value (i. e. , is neutral). Response conflict GREEN Incongruent > Congruent No response conflict > = HOUSE Neutral ORANGE Congruent Incongruent > Neutral Congruent >Neutral R L Last third The activity of four different medial frontal regions decreases with training, indicating that it becomes easier to reduce response conflict with practice. The activity of three different dorsolateral regions stays constant since an attentional set must be retained regardless of practice. Implications for Cognitive Disabilities Knowledge about how the brain regulates attentional control has important implications for: 1) understanding the nature of cognitive disabilities themselves, 2) for evaulating the efficacy of treatment programs and for 3) the design of devices that can improve the lives of individuals with attentional dysfunction. For example, our findings indicate that the design of an attentional aid should have two important attributes: a means to help the disabled person remain focused on information that is critical to performance of the task, and a means of helping them decide among the array of possible responses. Furthermore, our results suggest that as an individual becomes wellacquainted with a task, it might be possible to employ a more “streamlined” device that places less emphasis on the selection of responses. References Response conflict vs. none Cingulate activity when there is response conflict None vs. none No cingulate activity when there is no response conflict Baddeley AD, Baddeley HA, . Bucks RS, Wilcock GK. (2001). Attentional control in Alzheimer's disease. Brain. 124, 1492 -1508. Banich, M. T. , et al. (2000 a) f. MRI studies of Stroop tasks reveal unique roles of anterior and posterior brain systems in attentional selection. Journal of Cognitive Neuroscience, 12, 988 -1000. Banich, M. T. , et al. (2000 b). Prefrontal regions play a predominant role in imposing an attentional “set”: Evidence from f. MRI. Cognitive Brain Research, 10, 1 -9. Chan, RCK. (2001). Attentional deficits in patients with postconcussion symptoms: a componential perspective Brain Injury. 15(1), 71 -94. Cicerone KD, et al. . (2000). Evidence-based cognitive rehabilitation: recommendations for clinical practice. Arch Phys Med Rehabil. , 81, 1596 -1615. Cossa FM, Fabiani M. (1999). Attention in closed head injury: a critical review. Ital J Neurol Sci. 20, 145 -53. Milham, M. P. , et al. (in press). Attentional control in the aging brain: Insights from an f. MRI study of the Stroop task. Brain & Cognition. Milham, M. P. , Banich, M. T. , et al. (in press, b). The relative involvement of anterior cingulate and prefrontal cortex in attentional control depends on nature of conflict. Cognitive Brain Research. Milham, M. Banich, M. T. et al. (submitted). Practice-related effects demonstrate complementary roles of anterior cingulate and prefrontal cortices in attentional control. Psych. Sci. Paolucci S, et al. (2001). Mobility status after inpatient stroke rehabilitation: 1 -year follow-up and prognostic factors Arch Phys Med Rehabil. 82, 2 -8. Morris, R G. (Ed). (1996). In Attentional and executive dysfunction. Morris, RG. (Ed). The cognitive neuropsychology of Alzheimer-type dementia. (pp. 49 -70). New York, NY, US: Oxford University Press. Potter DD, Bassett MR, Jory SH, Barrett K. (2001). Changes in event-related potentials in a three-stimulus auditory oddball task after mild head injury. Neuropsychologia, 39, 1464 -72.
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