Basal ganglia circuitry tested

It is often said that the circuit of the basal ganglia is just a convenient way to summarise the motor deficits but there is no proof that is real. A way to demonstrate its features would be to be able to make changes that are correlated with motor behaviour. This has been done in mice (Kravitz et al., 2010). The authors combined two techniques: expression of genes specific for direct or indirect pathway medium spiny neurones and stimulation of neurones using  light. After the standard controls (the genetic modifications do not alter the physiology of medium-spiny neurones etc.), they go for the optostimulation. Selective activation of the direct pathway increases ambulation, activation of the indirect pathway induces freezing. All of these done in vivo.
This paper should be mandatory reading for neuroscience students.