Imaging studies of memory and attention

Attention mechanisms can be broken down into several components, including the modulation of early sensory cortex as a result of attention, the direction of attention modulation (attentional template), and the selection of responses. Objects can be selected on the basis of their component features or their location. Both mechanisms produce robust modulations in specialized regions of extrastriate visual cortex (e.g., color or motion-related regions) and in the parietal lobe, respectively. The neutral correlates for the attentional template remain unknown. Candidates include working memory circuits in frontal lobe and selective attention circuits that include the anterior cingulate. Regions of attentional template, response selection, and working memory may, in fact, overlap, making such distinctions difficult. The anterior cingulate may, alternatively, be more involved in the selection of responses when several options are available. Attentional mechanisms may also work across cognitive systems, with decreased activity in irrelevant sensory modalities, such as auditory or somatosensory cortex decreases during a visual task. The degree of this modulation may be influenced by unknown variables. In both memory and attention systems, imaging studies have shown that many regions of brain are active, with some increasing, and others decreasing during various tasks. Imaging studies offer the opportunity to understand the function of many 'silent' areas of brain, such as prefrontal or cingulate cortex. Understanding the function of these areas will be of obvious clinical importance to the neuro-surgeon.