Testing the importance of the retrosplenial navigation system: lesion size but not strain matters: a reply to Harker and Whishaw.

In their review on the retrosplenial cortex Harker and Whishaw [Neurosci Biobehav Rev, 2004] claim that there is continued disagreement over the importance of this region for navigation. They argue that discrepancies in the published effects of retrosplenial lesions reflect two principal variables, choice of rat strain and choice of spatial task. In this reply, evidence is provided showing that Harker and Whishaw [Neurosci Biobehav Rev, 2004] have created a misleading impression and, in fact, there is a clear consensus that the rat retrosplenial cortex is necessary for navigation. Likewise, there is no dispute that the effects of retrosplenial lesions will differ for different tests of spatial learning. While Harker and Whishaw [Neurosci Biobehav Rev, 2004] also conclude that choice of rat strain has a critical impact on whether a lesion-induced deficit is found, a comprehensive review of the published data shows no systematic strain difference. There is, however, growing evidence that when interpreting the effects of retrosplenial lesions, account should be given of the lesion method and its interaction with lesion size.