Control functions of the frontal lobes. Modularity of the central-supervisory system?

Lesions of the prefrontal cortex result in a wide variety of neuropsychological disorders. Despite recent advances, the executive processes and their functional architecture remain poorly specified. This study assessed control processes operating in novel, conflicting and combined tasks in patients with lesion of the prefrontal or posterior cortices. Experiments used two-choice reaction time tests with similar perceptuo-motor and decision processes. It mainly showed (1) impaired short term memory in posterior patients, and (2) impairment of response inhibition and tasks combination in some frontal patients. Selective deficits with double dissociations were evidenced on novel, conflicting and combined tasks. This study provides additional evidence for the prominent role of the frontal lobes in control processes. The demonstration of selective deficits of specific control processes suggests that executive functions depend on multiple separable control processes, and that their operations can be specified in cognitive terms.