Episodic memories in humans

Try to remember your last birthday party. What comes to your mind might include the guests arriving at the door, a good meal by the dinner table and the opening of presents in the living room, i.e. a recollection of a sequence of events that took place in specific locations (episodic memories). One of the most challenging goals of neuroscience is to understand how electrical activity in the brain facilitates the formation of memories of unique, non-repeating events (one-shot encoding), and how these memories can be mentally re-experienced.


How can we assess episodic memory functions? A large proportion of studies of memory uses animal models are used to study how neural activity relates to such memory processes. In these types of experiments, brain activity is measured while animals are performing behavioral assays that allow for the robust readout of memory performance. Despite significantly contributing to our understanding of the neural processes underlying memory formation and retrieval, this approach has inherent limitations. Re-experiencing the past is an inherently subjective process that in its entirety cannot be studied through behavioral readouts alone. In contrast to studies in animals, humans have the unique ability to describe what they are experiencing, thinking, and remembering on a moment-to-moment basis. This is the reason why a complete understanding of the neural mechanisms underlying the subjective re-experience of the past affords both the tools used in behavioral animal research as well as the rich reports that can be obtained in humans.

How will we study the relationship between neural activity and memory processes in humans? We will use electrodes placed (for clinical reasons) in the medial temporal lobe of patients with epilepsy to record neural activity during memory formation and recall. Electrodes placed within brain tissue make it possible to measure neural activity on a single neuron level. We aim to relate the measured activity directly to the reported subjective experience of an episodic memory.

Our vision is to progress our understanding on how the human brain acquires, organizes, and retrieves episodic memories. Since the human brain is the most complex biological system we know, this is a crucial step as one of the main goals of neuroscience is to understand how the brain performs higher cognitive functions, and ultimately how these functions are disturbed in cognitive disorders. For several reasons our approach is vital to translate animal findings and insights into an enhanced description of the mechanisms underlying cognitive functions in humans. First, we will test whether the hypotheses that have emerged from animal studies can account for psychological phenomena in humans. Second, we will record neural activity in the area first affected in the progression of Alzheimer’s disease. For this reason the project can potentially contribute to the development of more appropriate animal models for human brain diseases. In the future, such knowledge may increase the likelihood of finding a treatment that can stop or prevent the development of memory disorders.

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