Grid cells in the medial entorhinal cortex (MEC) encode location through firing fields that form grid-like maps of the environment. At the same time network activity in the MEC is dominated by oscillations in the theta (4-12 Hz) and gamma (30-100 Hz) bands. The relationship between oscillatory activity and grid firing is not known. Our recent experimental data established that feedback inhibition between excitatory stellate cells and inhibitory fast spiking interneurons dominates the synaptic connectivity in layer II of the MEC. To determine if this circuit is sufficient to explain both the network oscillations and grid firing fields, we constructed a network of model stellate cells and interneurons. In this model, stellate cells connect exclusively to interneurons, while interneurons contact only stellate cells. We show that external excitatory conductances can drive the network into an attractor state. Feedback inhibition onto the model stellate cells has a synchronizing effect. Synaptic input to both populations of neurons is synchronized in the gamma frequency range (30 - 100 Hz). When coupled with a theta modulated external drive (8 Hz), we observed network synchronization during the trough of the theta signal only. When the borders of the network are connected with a twisted torus topology (Guanella et al. 2007) and velocity modulated inputs are applied to the circuit, excitatory neurons in the circuit generate grid-like firing fields. Due to limited stability of the attractor, the grid fields were blurred. However, it was possible to obtain stable grid fields by including a place cell resetting mechanism as an additional input to the network (Guanella et al. 2007). These results demonstrated that the same local circuit architecture - feedback inhibition - supports emergence of attractor states and nested gamma oscillations. This has implications for mechanisms of both formation of grid-like receptive fields as well as population coding and information transmission between brain areas.
|Journal||Frontiers in Computational Neuroscience|
|Publication status||Published - 2012|
|Event||The Bernstein Conference on Computational Neuroscience 2012 - Klinkum rechts der Isar, Munich, Munich, Germany|
Duration: 12 Sep 2012 → 14 Sep 2012