ABSTRACT
Studies of patients with brain lesions have provided the foundations of our knowledge about the biological organisation of human memory. Lesions have produced dramatic and often unexpected mnemonic deficits that provide clues about which brain regions are necessary for which memory processes. The behaviour of memory-impaired patients with brain lesions, however, does not delineate what process the injured tissue subserves. The behaviour reflects what uninjured brain regions can accomplish after the lesion. In addition, naturally occurring brain lesions often impair multiple brain systems, either by direct insult or by disconnection of interactive brain regions. It is therefore difficult to determine which defect is the consequence of which part of a lesion. Despite that, lesion studies continue to provide new evidence-functional neuroimaging studies using positron emission tomography (PET) or functional magnetic resonance imaging (fMRI) now permit the visualisation of memory processes in the healthy brain. The goal of some of this work has been to “map” the brain in the sense of
assigning specific function to structures by selectively activating or deactivating them while people perform various tasks. It is important to acknowledge that what is measured is not neuronal activity but local haemodynamic changes such as blood flow, in the case of PET, and blood oxygenation in the case of fMRI.
