Away from Discrete Areas Arranged in Hierarchies

The following properties of cortical organization are now nearly universally accepted: 1. The cerebral cortex is divisible into more or less sep-arate areas, each of which tends to emphasize a dif-ferent type of information. 2. Some areas contain an internal, finer organization of the relevant information such as a retinotopic map of the visual world or a somatotopic map of the body. 3. Cortical areas do not function as separate modules but rather are organized into large, densely intercon-nected networks that function together, such as the network of extrastriate visual areas or the network of motor areas. 4. Within these larger networks of areas, some areas are hierarchically above other areas, processing informa-tion that is more abstract and more removed from the sensory or motor devices of the periphery. This view of cortical organization, based largely on the visual system of primates (e.g., Felleman and Van Essen 1991; Kaas and Garraghty 1991), is more or less accurate but may be incomplete. It fits the lower levels of visual processing, but the higher levels of visual pro-cessing may not fit neatly into the concept of separate areas (e.g., Haxby and others 2001). The situation becomes even more problematical in the cortical motor system. Published maps of the motor sys-tem (see Fig. 1) resemble maps of the visual system, with a topographically organized primary area that is linked to the periphery and a range of higher-order areas that are assigned functions such as “planning ” and “sequencing