Theta Oscillations and Recognition Memory in Young and Older Adults

Abstract

A dual-process theory postulates that familiarity and recollection are the two distinct components of recognition memory. The Aggleton and Brown (1999) model predicts that these two retrieval processes are supported by dissociable temporal-thalamic systems, where the hippocampal–anterior thalamic (AT) and perirhinal-medial dorsal (MD) axes are responsible for recollection and familiarity, respectively. It has been suggested that recollection is selectively impaired with normal ageing, while familiarity remains relatively unaffected. By adopting a technique measuring the relative involvement of different corticolimbic circuits in mnemonic tasks (Kirk & Mackay, 2003), we examined 4-7 Hz theta EEG activity associated with familiarity and recollection separately, in combination with an examination of the effect of normal ageing on recognition memory. During the experiment, subjects participated in two different mnemonic tasks, each reliant on familiarity judgement and episodic recollection, respectively. The results indicated that familiarity and recollection were distinct from one another in terms of theta-synchronised time course and underlying neural sources. It was found that familiarity was a fast-acting and parietal lobe-dependent process, whereas recollection was found to be a slower and frontal lobe-dependent process. Although we did not find direct evidence for the hippocampal-AT network proposed by Aggleton and Brown (1999), the results of the current study partially support the perirhinal- MD network by showing an involvement of the perirhinal cortical regions during the familiarity judgement task. The young and old groups exhibited similar theta activity patterns as well as behavioural performance level in both task conditions, indicating that neither component of recognition memory was impaired in the older subjects. Intact recollection in the old group may be explained in terms of a ‘compensatory mechanism’, which was observed as increased theta power over the prefrontal cortex. Overall, the present data support dual-process models of recognition memory and suggest that recognition memory is not affected by normal ageing.