The role of intra-striatal synaptic interactions for shaping cortico-striatal network dynamics

The basal ganglia consist of several interconnected subcortical nuclei that are supposedly involved in many motor and cognitive functions. The striatum, the input stage of the basal ganglia, is a major recipient of massive glutamatergic inputs from the cerebral cortex and thalamus. Medium spiny neurons (MSNs) dominate in the striatum (up to 95% in rodents). They are inhibitory (GABAergic) and have membrane properties that give them a high threshold for activation [1]. MSNs interact with each other through weak recurrent inhibitory synapses and with low connection probability [2]. Fast-spiking GABAergic interneurons (FSNs) can delay or prevent the emission of an action potential in MSNs [3]. FSNs receive convergent inputs from a wider range of distinct cortical regions compared to nearby MSNs, and despite the fact that they are relatively sparse elements (1-2%) it seems that they have very prominent role in shaping the output of the striatum [4].

Neuronal avalanches are a type of spontaneous activity first observed in vitro by recording local field potentials in cortical neural networks using slices of rat cortex as well as cultured networks [5]. Propagation of spontaneous activity is balanced and shows a branching parameter close to 1. In addition, the number of electrodes driven over threshold during activity is distributed approximately like a power law with an exponent of -3/2 for event sizes suggesting a critical dynamics [5]. Neural avalanches have been shown to provide: optimal information transmission [5, 6], maximal information capacity [6] and maximal dynamic range [7].

We are studying simultaneously striatal and cortical activity in vitro. Preliminary results show that neuronal avalanches in cortex induce activity clusters in striatum whose size distribution can be approximated by a steeper power law than observed in cortex. Based on this we have developed network models in order to determine the impact of different striatal neurons on the more negative exponent. In particular, we are investigating whether FS or MS neurons have any roles in shaping the striatal dynamics.

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