Illustrating cerebral function: the iconography of arrows

For over a century the arrow has appeared in illustrations of cerebral func tion, yet the implications of using such symbols have not been previously c onsidered. This review seeks to outline the nature, evolution, applications and limitations of this deceptively simple graphic device when it is used to picture functions of the brain. The arrow is found to have been used in several different ways: as a means of endowing anatomical structures with functional properties; as a method o f displaying neural function either in free-standing form or in a structura l or spatial framework; as a device for correlating functional data with un derlying brain topography; and as a technique for linking functions of the brain with the world outside and with various philosophical concepts. For many of these uses the essential feature of the arrow is its directiona l characteristic. In contrast to the line, it is direction that enables the arrow to display information about time, which in turn can be exploited to depict functional rather than structural data. However, the use of the arrow is fraught with difficulties. It is often unc lear whether an arrow has been used to illustrate fact, hypothesis, impress ion or possibility, or merely to provide a decorative flourish. Furthermore , the powerful symbolic nature of the arrow can so easily confer a spurious validity on the conjectural. Increasingly now there are insuperable difficulties when attempting to illu strate complex mechanisms of brain function. In the iconography of cerebral function, therefore, arrows with all their ambiguities may in certain circ umstances become superseded by more non-representational symbols such as th e abstract devices of the computational neuroscientist.