Decoding the Direction of Movements from Interneuron and Projection Cell Populations in the Basal Ganglia

Neuromotor prostheses (NMPs) seek to replace motor functions in paralyzed humans by controlling external devices directly from recording contacts placed within the brain (in effect, bypassing the damaged neural tissue). Studies to date have focused on cortical areas for NMP control, but deeper brain structures have also been implicated in generating motor commands. Recent studies combining non-invasive brain computer interface (BCI) experiments with functional brain imaging have revealed that the hemodynamic response related to activity of the Basal Ganglia (BG) increases significantly during BCI control. The BG has long been theorized to be involved in the selection of motor actions in the neocortex, and may be an ideal location for a discrete state NMP. In this report, we investigate the directional information contained in the firing rates of cells within the nuclei of the BG. Four Long-Evans rats performed a directional nose poke task while action potentials were recorded from 21 drivable tetrodes. Our preliminary analysis has identified 16 candidate interneurons and 8 primary cells from properties of the extracellular waveforms, and has determined the amount of directional information in each cell. Using an unsupervised classification decoder of the firing rates in the BG, we could predict the animal's movement direction correctly in >80% of the trials. We further analyzed the cell ensemble decoding and found that the proposed interneuron's directional information peaked ~100-175ms before the projection cells. The fast spiking interneurons of the striatum may be an important control source for NMPs as these cells are thought to play a large role in the selection of actions.