In the other pathway, the putamens' projection to the SNpc is destroyed. This causes increased firing of dopamine neurons, which synapse back on the putamen. This activates inhibitory neurons from the putamen to the GPi. Thus, the same inhibitory neurons as in the first pathway, going from the GPi to the thalamus and brainstem, are disinhibited. Again the result is excess motion.
Striatal atrophy results in hydrocephalus ex vacuo, literally meaning water-head.
Hydrocephalus is the enlargement of cerebral ventricles and thinning of cerebral substance. As the brain atrophies, space is created in the brain, and it needs to be filled with something. That something is extra cerebrospinal fluid, the liquid normally found in the ventricles. The striatum is not the only part of the brain to atrophy. Both parts of the globus pallidus, the subthalamus, and the cerebral cortex decay as well.