Psychiatry: Attention

Attention

In view of what is known about the role of the prefrontal cortex, it is readily apparent that the primary role of this brain region involves the integration and modulation of cognitive function-ing. Given the onerous task of managing vast amounts of incom-ing and outgoing information, it stands to reason that attentional abilities are of great importance to frontal lobe functioning.

The area of attention as it relates to the frontal lobes has pro-vided a rich field of study. Like many of the other general areas of cognition (e.g., memory, language), attention represents a vast and complex phenomenon. This is, in part, due to the many facets of at-tention itself. Underlying all cognitive activity, there must be some tonic form of activation that provides the background in which all other cortical activity occurs. Luria (1973a) referred to this capac-ity as his first functional brain area and noted that the reticular activating system in the brain stem provided the core structure sub-serving brain activation. In general, this is referred to as alertness or wakefulness. However, one’s ability to pay attention to specific stimuli is thought to be subserved by higher cortical areas, includ-ing the prefrontal cortex. The psychological process of attention can broadly be defined in terms of divided, focused and sustained abilities. Divided attention occurs when multiple stimuli are at-tended to simultaneously. We can often find ourselves participating in divided attention tasks at parties when we tune into two different conversations at one time. Focused attention refers to the ability to inhibit irrelevant stimuli in the service of attending to a particular stimulus. Often this type of attention requires one to inhibit auto-matic responses that conflict with the task at hand. Sustained atten-tion requires the ability to maintain attention over time.

As suggested earlier, Mesulam (1990) has proposed a neurocognitive network of attention involving a number of neural circuits participating in PDP. According to this model, interactive, multifocal neural pathways that are both localized and distributed give rise to multiple possibilities and flexibility with respect to attentional behavior. Much of this model is based on neglect be-havior, which can be separated into perceptual, motor and limbic components. In general, the perceptual component refers to the di-minished awareness that a sensory event has occurred within the neglected field, the motor component refers to the diminution or ab-sence of exploratory behaviors, and the limbic component refers to a devaluation or amotivation of the neglected hemispace. Accord-ing to Mesulam, neglect behavior in both humans and monkeys consistently follows lesions to one of three areas: the dorsolateral parietal cortex, the dorsolateral premotor–prefrontal cortex and the cingulate gyrus. These three areas provide local networks that provide the basis for a large-scale neural model of attention. Each local network or component participates in mapping the environ-ment in slightly different ways. For example, in the case of visual hemineglect, Mesulam suggested that the posterior parietal cortex provides sensory (visual) awareness, the prefrontal area provides a map of exploratory movements (i.e., eye movements), and the cin-gulate gyrus provides a map for assigning value to the spatial co-ordinates. Within these areas, specific cytoarchitectonic structures interact through extensive reciprocal and monosynaptic connec-tions. In the area of the dorsolateral prefrontal cortex, the frontal eye fields (Brodmann’s area 8) play a critical role in directed attention. Although lesions in other brain regions, such as subcortical struc-tures, are known to cause neglect, these areas have been found to connect to at least two of the three central components.