Chapter 51: recovery of function: redundancy and vicariation theories.

Redundancy and vicariation theories were employed by 19th-century practitioners and animal researchers to account for what seemed to be sparing and recovery of function after brain damage. Those individuals believing in redundancy maintained that there are duplicate or back-up areas that can mediate a function after brain damage, such as the homologous region on the opposite side of the brain. In contrast, vicariation theorists argued that brain areas with different functions could sometimes assume or "take over" the functions of injured areas. This chapter looks at the history and early evidence for these two different views, and how theorizing changed as more was learned about cortical localization of function. It reveals that there were subtle variations on these basic themes and that certain factors, such as age at the time of brain injury, were often brought into the equation. With limited knowledge and inadequate methodologies, the debates about recovery of function that flared up during the late-19th century would not be quickly or easily rectified.