Developmental amnesia: Dissociations in long term memory

Our initial studies in children with bilateral damage to the hippocampus arising from hypoxia/ischaemia revealed a pronounced dissociation between episodic memory, which is markedly impaired, and semantic memory, which is relatively preserved.  We labeled the syndrome 'developmental amnesia' in order to differentiate it from the more global anterograde amnesia usually seen after bilateral medial temporal lobe damage incurred in adulthood.  A series of follow-up studies will be reported to examine some of the variables leading to the developmental syndrome and to investigate further some of its defining features. The findings indicate that the syndrome is directly related to the extent of bilateral hippocampal pathology but is independent of the age during childhood when this damage occurs. The resulting form of amnesia is characterized by a dissociation not only between the episodic and semantic components of cognitive memory but also between recall, which is severely affected, and recognition, which remains relatively intact.  Behavioural, electrophysiological, and functional neuroimaging findings in one of the patients (Jon) lead to the proposal that developmental amnesia occurs when the neural mechanism underpinning the mnemonic process of 'recollection', as contrasted with 'familiarity', is selectively compromised.