Download or read book Development of Spatial Memory in the Entorhinal Cortex Through Neural Mechanisms of Self-organization written by Himanshu K. Mhatre and published by . This book was released on 2011 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: How does the brain learn to navigate in the world? How do maps develop that can represent the large spaces in which animals navigate? Grid cells in the dorsal segment of the medial entorhinal cortex (dMEC) show remarkable hexagonal activity patterns as a rat navigates an open field. Furthermore, there exists a gradient of spatial scales along the dorsoventral axis of the dMEC, with neighboring cells sharing the same spatial scale but having offset spatial phases while maintaining the same orientation. Past studies have suggested multiple mechanisms explaining how grid cells firing fields can develop hexagonal structure. The GRIDSmap model that is introduced in this thesis contributes to an understanding of how such hexagonal structures may be learned as an animal navigates through the world. In particular, the GRIDSmap model shows how hexagonal firing fields may be learned by a self-organizing map whose inputs come from multiple one-dimensional small-scale stripe cells that integrate linear velocity signals in different directions, and whose learned categories are grid cells in layer II of dMEC. GRIDSmap cells learn this hexagonal structure from a simple trigonometric property of space that is manifested in the most frequent co-occurrences of stripe cell firing. The GRIDSmap habituative dynamics that control map learning also generate membrane potential oscillations. Faster (slower) oscillations lead to learning of smaller (larger) grid scales, consistent with experimentally observed oscillations in dMEC layer II stellate cells. Such multiple scales of grid cells can induce learning of hippocampal place cell firing fields that represent much larger scales; namely, the least common multiple of the grid cell scales. This hierarchy of entorhinal and hippocampal maps clarifies how path integration signals may give rise to place fields capable of representing the large spaces that animals can successfully navigate.