Encoding and the frontal lobes: a dissociation between retrograde and anterograde memories

Recent functional neuroimaging studies have suggested that different neural substrates within the frontal lobes are associated with memory encoding, retrieval and monitoring. If this is the case, then it should be possible to find frontal patients with selective deficits to these processes. However, most laboratory based memory tests (e.g. Wechsler Memory Scale) require a combination of all these processes making it hard to find clear dissociations between patients. Using tests of everyday memory, this study documents a clear dissociation between a frontal patient's (JB) impaired ability to retrieve events from the anterograde period relative to spared ability to retrieve events from the retrograde period. This is consistent with specific disruption to frontal mechanisms associated with encoding which disrupts the formation of new episodic memories. The defective mechanism may be related to more general aspects of cognitive processing (e.g. selection demands), but it is unlikely to reflect damage to working memory (as assessed by the n-back task) as there is a clear dissociation between spared performance on this task and impaired performance on a comparable episodic recognition memory task.