Antidepressive Agents--therapeutic use Antipsychotic Agents--therapeutic use Basal Ganglia--drug effects Cannabinoids--therapeutic use Cholinesterase Inhibitors--therapeutic use Excitatory Amino Acid Antagonists--therapeutic use GABA Agonists--therapeutic use Humans Huntington Disease--drug therapy Neuroprotective Agents--therapeutic use Tetrabenazine--therapeutic use