Abstract
In recent years, the concept of working memory has gained popularity in many fields of cognitive neuroscience. Working memory refers to a brain system that provides temporary storage and manipulation of information necessary for complex cognitive tasks. The system consists of two slave systems (the phonological loop and the visuospatial sketchpad) and the central executive. The central executive is a kind of a control center to select and/or integrate information provided by these two slave systems and is a vehicle of decision for appropriate motor behavior or judgment. Recently, I had an opportunity to see a patient with bilateral frontal lobe infarcts with a symptom that has not yet been documented in the literature. He complained a severe difficulty in making a phone call. On examination, he demonstrated extreme difficulty in pointing to a series of numbers, although he had normal vision, normal motor and sensory functions, fair auditory memory for numbers and memory for spatial span. Based on a number of tests, I concluded that the patient's principal disorder was difficulty in converting one mode of information into another mode of information. The present patient's symptom mentioned above can be best explained in terms of a working memory paradigm. Although individual modal systems, or slave systems, retained nearly normal function, simultaneous holding of heteromodal information and its modal transformation in the central executive system seemed to have been at fault. The function of central executive may be related to the prefrontal regions.
