Disordered integration of heteromodal short-term cognitive operations: A breakdown of working memory

We report a patient with bilateral frontal lobe infarcts with a symptom that has not yet been documented in the literature. He complained of 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, we concluded that the patient's principal disorder was difficulty in converting one mode of information into another mode of information. This unexpected symptom 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.