Interneuro Plasticity During Spatial Learning

The hippocampus is a brain region, which is important for learning and memory formation. Neurons in the hippocampus form complex neuronal circuits in which the activity of excitatory cells is governed by many anatomically-different inhibitory cell types. The majority of hippocampal excitatory cells encode spatial information: they are active in specific areas of the surrounding environment with each cell being active in different locations. These cells, also referred to as place cells, play important roles for spatial learning because the cognitive map formed by them helps animals to reach desired locations of an environment. When animals have to learn new target locations that they need to reach, the cognitive map and the coding properties of place cells change with learning. Surprisingly, such reorganisation of the coding of excitatory place cells also involves changes in inhibitory cells. Inhibitory cells also alter their activity during spatial learning and the strength of the input they receive from excitatory cells also change. The aim of this research proposal is to understand the behavioural conditions which are accompanied by input changes to inhibitory cells and to examine whether different types of inhibitory cells behave differently during new spatial memory formation. Moreover, we will probe the role of such changes in spatial memory formation, which requires updates of the cognitive map and place cell coding. Overall this work aims at improving our understanding of the circuit-wide changes that enable spatial memory formation.

The hippocampus is a brain area, which is important for spatial memories. Hippocampal principal cells encode space by firing in a location-dependent manner. Together these place cells form an allocentric map representation of space. New maps can be formed in novel environments or as a result of spatial learning. This new map formation is accompanied by plastic changes of pyramidal cell-interneuron connections. Here, combined in vivo electrophysiology and optogenetic approaches were used to test plastic changes on interneurons and the role of interneurons in circuit function. In these experiments, the use of optogenetic techniques enabled us to differentiate specific interneuron types. Overall our work showed that with our optogenetic manipulation, we can induce plastic changes in interneuron circuits. Furthermore, we demonstrated that interneurons are involved in regulating the expression of complex cellular network activity patterns.