Topography of cognition: parallel distributed networks in primate association cortex.

The association cortices, those regions interposed between the primary sensory and primary motor areas, are thought to mediate a variety of cognitive functions. Among these, the prefrontal cortex has traditionally been considered the least understood and most complex. The only point that seems to marshall agreement among basic neuroscientists is that prefrontal functions and operations, acknowledged to be important in human behavior, are less accessible to analysis than are many other areas of the cortex. One reason for this perception may be the lack of an agreed upon anatomical blueprint that firmly establishes the relationship between prefrontal cortex and other, better understood, parts of the brain. However, this circumstance has changed radically in the last decade, and the structure and functions of the frontal lobes, particularly the prefrontal "silent" portion, which have intrigued investigators since the last century (Ferrier 1886, Bianchi 1895, Franz 1907), have recently again become the subject of intense interest (for reviews, see Damasio 1979, Fuster 1980, Goldman-Rakic 1984, 1987, Milner et al 1985, Mesulam 1986, Ingvar 1983, Stuss & Benson 1984). The availability of solid new findings in experimental animals and human patients and the promise of further discoveries are undoubtedly the basis of this renewed interest. Several extraordinarily influential papers paved the way for the modern era of frontal lobe research. Without a doubt, anatomical studies of pre­ frontal cortex were stimulated by Nauta's 1971 paper on "The Problem of the Frontal Lobe: A Reinterpretation." This review made an indelible impression both for its eloquence and fundamental validity, suggesting as