Spatial cognition is one of the fundamental cognitive abilities necessary for mammals to survive in the environments. The hippocampus of the mammalian brain is considered to be the neural substrate of a cognitive map. But how do mammals build such cognitive maps is still elusive. The recent discovery of grid cells in the medial entorhinal cortex (MEC) of rodents, bats as well as humans suggests that the MEC provides key inputs for the hippocampus, by integrating movement information and landmark information. Each grid cell fires strongly when the animal enters locations that define the vertices of a triangle grid. Some of the grid cells show grid firing patterns only when the animal runs along particular directions.

In this talk, I will present an attractor network model that accounts for the conjunctive position-by-velocity selectivity of grid cells. We propose that grid cells collectively represent arbitrary conjunctions of positions and movements of the animal. Due to asymmetric recurrent connections, the network has grid patterns as states that are able to move intrinsically with all possible directions and speeds. A velocity-tuned input will activate a subset of the population that prefers similar movements, and the pattern in the network moves with a velocity proportional to the movement of the animal in physical space, up to a fixed rotation. Thus the network 'imagines' the movement of the animal, and produces single-cell grid firing responses in space with different degrees of head-direction selectivity. We propose testable predictions for new experiments to verify our model.

Bio. of Dr. Bailu Si: Dr. Bailu Si finished his first degree in computer science. Later he became interested in vision and pursued a PhD in theoretical neurophysics in the University of Bremen, Germany. After his PhD study, he held postdoctoral researcher positions first in the International School for Advanced Studies in Italy, and later in the Weizmann Institute of Science in Israel. Since December 2013, he is a group leader in the Shenyang Institute of Automation, CAS. In recent years, he investigates theoretical questions of spatial cognition and action selection in uncertain environments.