A Computational Model of the Hippocampus

Exhibitor: Catherine Geraghty

Supervisor: Janet Wiles

Research Group: Complex and Intelligent Systems

Industry Sector: Scientific / Research Services

The aim of the project was to create a simplified computational model of the hippocampal formation. This simplified model was found to have comparable functionality to other more complex models. The simplified model was used to answer two questions: how many patterns could the model recall before degradation occurred and to what accuracy could the network recall input patterns given partial input? After the point of degradation was determined and the accuracy of reconstruction from partial input was measured, each component of the model was then ‘lesioned’. The structures were ‘lesioned’ to gain insight into their behaviour. The project found that the hippocampus model degraded as more input patterns were presented. A recency effect was also found where the most recently presented patterns were remembered better. Results from lesioning the DG, CA1 and CA3 gave some insight into the possible function of each structure. It was also found that the network was able to reconstruct whole patterns from 50% of the original, to an acceptable accuracy.

Memory is an abstract concept that can be defined as the ability to remember the past in both a defining and unifying way (Squire & Kandel, 1999). There are two major brain structures involved in human memory: the cerebral cortex and the hippocampus. The hippocampus is considered crucial for unifying memories while the cortex is responsible for storing the memories (Rosenzweig, Leiman, Breedlove, 1999).

Research has found that the hippocampus is necessary for the formation of new memories, in particular declarative memories (Rosenzweig, Breedlove & Leiman, 2002). There are two types of human memory; declarative/explicit and procedural/implicit (Matlin, 1995). Procedural memory is concerned with the particular processes used in learning and these are often implicit or unconscious. This type of memory still remains intact in patients with hippocampal amnesia (Cohen & Eichenbaum, 1993). Declarative memory on the other hand is concerned with the accumulation of facts and data from learning experiences and is explicit or conscious (Cohen & Eichenbaum, 1993). Declarative memory is severely damaged in patients with hippocampal lesions (Cohen & Eichenbaum, 1993). These findings show that the hippocampus is vital for the creation of declarative memories.

Thesis Document (PDF)