The role of prestimulus brain activity in long-term memory encoding

• Main Author: Gruber, M. J.
• Published: University College London (University of London) 2011
• Subjects: 616.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.625673

It has been shown that brain activity before an item can predict whether this item will later be remembered. However, the cognitive mechanisms underlying this so-called prestimulus brain activity are poorly understood. The studies in this PhD thesis addressed the role of prestimulus neural activity in long-term memory encoding and whether this activity is under voluntary control. To allow better dissociation between brain activity before and after an item, electroencephalography (EEG) was used due to its high temporal resolution. In a series of studies EEG data were analyzed in terms of Event-Related Potentials (ERPs) and oscillatory power in the theta frequency band (4-8 Hz) that plays a crucial role in memory processes. The findings demonstrate that brain activity preceding a stimulus is indeed under a person‟s control. In one experiment, ERP and frontal theta prestimulus activity before an item was only evident when participants were highly motivated to encode an upcoming item. In another experiment, ERP prestimulus activity only emerged when participants prioritized encoding over a concurrent task. These studies suggest that, at least, some prestimulus activities reflect preparatory processes that depend on the available cognitive resources. Two further experiments demonstrated that frontal prestimulus encoding-related theta power is specific to semantic encoding conditions. Finally, a series of behavioural experiments showed that memory performance does not differ depending on the opportunity to prepare during encoding. The findings of my PhD thesis suggest that (i) some prestimulus signals (i.e. frontal theta) reflect a preparatory process ahead of semantic encoding, (ii) and, most importantly, prestimulus signals (i.e. ERPs and frontal theta) reflect active preparatory processes for long-term memory formation. The results of this thesis could lead to the development of new strategies of how to improve memory, especially in clinical settings.