Cortical electrophysiology of human episodic memory
Abstract/Contents
- Abstract
- In any given day, we encounter events or episodes that are more memorable (better encoded) than others. The memorability of a given event can be experimentally measured by the degree of difficulty (speed, confidence, accuracy) in which that episode is brought back to mind (retrieval). Through lesion and animal model studies we have gained a core understanding of what parts of the brain are involved in these behavioral processes. However, the temporal dynamics and cortical spatial specificity of memory encoding and retrieval mechanisms remain a debated topic in neuroscience. Furthermore, much of our knowledge comes from correlational and indirect measures of brain activity. In Chapter 2 of my work, we leveraged direct recordings from the human cortical surface to study memory processes at a spatial and temporal resolution that remains rare in humans. When participants were tasked to recognize previously presented stimuli, we observed a temporal cascade of activity in the left parietal region of the brain. The intraparietal sulcus (IPS) traverses the parietal lobe and shows greater activity for previously seen items starting ~300ms after probe onset and returns to baseline 200ms before a memory decision is made. On the other hand, a more dorsal region, the superior parietal lobe (SPL), while initially active for both old and new stimuli, remains active through the behavioral response only for new stimuli. These observed cortical temporal dynamics advance theoretical models of the different roles of these parietal regions in remembering. In Chapter 3 of my work, I focused on investigating the causal role of oscillatory activity in the cortex for memory formation. A prevalent theory posits that opposing phases of the theta rhythm should promote states of optimal encoding or retrieval. However, direct evidence for these theorized effects remains scarce. In my work, we induced the theta rhythm in the dorsal prefrontal cortex through transcranial alternating current stimulation. Employing a closed-loop protocol, to-be-learned stimuli were presented at specific phases of the stimulated theta oscillation. Memory for the presented stimuli was later probed, and we analyzed remembered and forgotten stimuli as a function of encoding stimulation phase. Consistent with the theory, we found that memory strength is modulated by phase, such that stronger memories are aligned to $225^o$ of the stimulated theta phase. The nature of the experiment establishes a causal role for theta-phase alignment in effective memory formation. Together, my work advances understanding of the electrophysiology of human episodic memory through direct cortical recordings and electrical stimulation.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2017 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Gonzalez, Alexander |
|---|---|
| Associated with | Stanford University, Department of Electrical Engineering. |
| Primary advisor | Wagner, Anthony David |
| Thesis advisor | Wagner, Anthony David |
| Thesis advisor | Ganguli, Surya, 1977- |
| Thesis advisor | Lee, Jin Hyung |
| Thesis advisor | Norcia, Anthony Matthew |
| Advisor | Ganguli, Surya, 1977- |
| Advisor | Lee, Jin Hyung |
| Advisor | Norcia, Anthony Matthew |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Alexander Gonzalez. |
|---|---|
| Note | Submitted to the Department of Electrical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2017. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2017 by Alexander Gonzalez
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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