In PD, because of the loss of the dopaminergic nigrostriatal connection, the basal ganglia neurons, including the STN, fire by low-frequency oscillatory bursts and fire in synchrony. Under normal conditions, the basal ganglia neurons fire irregularly. The reciprocal pallido-subthalamic connection can be mimicked in vitro and is capable of burst firing. This pattern can be influenced by co-cultures of striatum and cortex (Plenz and Kitai 1999). The observed bursting activity was unaccompanied by synchronous activity in STN slice preparations after the addition of glutamate, dopamine, GABA, or muscarine receptor agonists and/or antagonists. Therefore, synchrony of STN activity in the parkinsonian state is dependent on its extrinsic connections (Wilson et al. 2004). Dissociation of central nervous system areas of P1 (day 1 postnatal) rat pups makes it possible to culture these neurons in a chemically defined medium (Heida 2003). By placing these cultures on MEAs, their spontaneous electrical activity can be recorded. By using polyethylenimine as substrate, a seemingly monolayered network can be created in culture on the MEA (see Rutten et al. 2001 for an overview).