With the ageing population comes an increase in dementia and memory-related disorders. Investigations of memory formation can facilitate insights into more effective treatments for this growing problem. Deep brain stimulation (DBS), the delivery of electrical stimulation to modulate brain activity, presents an exciting opportunity to investigate mechanisms of memory formation and potentially alleviate memory loss. One critical question with regards to DBS is when and where to stimulate.

Treatment for individuals with epilepsy who require resection surgery usually involves the implantation of electrodes in mesial temporal lobe structures (MTL), locations known to be involved in memory formation. This provides a unique opportunity for researchers, in a controlled setting, to record and stimulate the brain to investigate memory formation. Episodic memory, our recollection of personal experiences, can be tested through visual cues (presenting a stimulus and saccadic eye movements (SEM) during memory task). We used a model of how the brain can separate encoding and retrieval states to inspire our approach to try and optimize DBS timing delivery. Our objectives were to 1. Determine which visual stimulus is most relevant for timing stimulation, and 2. Determine the effects of such stimulation.

In this thesis, we identified that eye movement in response to a visual stimulus is a more appropriate timing cue than image presentation. In fact, through work with single-unit activity, we found inhibition of activity during the SEM. Our results suggest the SEM in MTL results from an internally generated movement not previously probed in mnemonic structures. Finally, we were able to investigate the effects of contingent stimulation on the SEM. This stimulation resulted in memory impairment. By customizing stimulation delivery contingent on an individual’s timing of the electrophysiological response post saccade, we saw no difference in memory performance between stimulation and no stimulation We successfully established eye movements as an important timing mechanism in MTL structures. Furthermore, stimulation contingent on eye movements can modify memory. These contributions support the potential to look at eye movements as a window on stimulation for investigating, modifying, and hopefully improving memory formation.