basal ganglia, whereas the other half express dopamine D2 receptors that project indirectly to the substantia nigra via the globus pallidus and subthalamic nucleus to form the indirect pathway of the basal ganglia. The remaining 5% of cells are interneurons that are either cholinergic neurons or one of several types of GABAergic neurons. The axons and dendrites of these interneurons stay within the striatum. The caudate nucleus and putamen receive excitatory information from all areas of the cerebral cortex. These glutamatergic inputs are generally topographically arranged such that the putamen takes information largely from the sensorimotor cortex, whereas the caudate nucleus obtains information largely from the association cortex. In addition, the dorsal striatum receives excitatory inputs from other brain structures like the thalamus, and minor excitatory inputs from the hippocampus and amygdala. The dorsal striatum contains neurochemically defined compartments called striosomes (also known as patches) that exhibit dense μ-opioid receptor staining embedded within a matrix compartment that contains higher acetylcholinesterase and calbindin-D28K. The dopaminergic axon terminals of the nigrostriatal pathway synapse onto GABAergic MSNs in the dorsal striatum. They form synapses on the cell body and dendritic shaft regions but mostly on the necks of dendritic spines that also receive glutamatergic input to the heads of the same dendritic spines. Function The main function of the nigrostriatal pathway is to influence voluntary movement through basal ganglia motor loops. Along with the mesolimbic and mesocortical dopaminergic pathways, the nigrostriatal dopamine pathway can also influence other brain functions, including cognition, reward, and addiction. Nigrostriatal dopaminergic neurons exhibit tonic and phasic patterns of neuronal firing activity. This can lead to different patterns of dopamine release from the axon terminals in the dorsal striatum and also from the cell body (soma) and dendrites in the SNc and SNr. As well as releasing dopamine, some axons in the nigrostriatal pathway can also co-release GABA. The nigrostriatal pathway influences movement through two pathways, the direct pathway of movement and the indirect pathway of movement. Direct pathway of movement The direct pathway is involved in facilitation of wanted movements. The projections from dopamine D1 receptors containing medium spiny neurons in the caudate nucleus and putamen synapse onto tonically active GABAergic cells in the substantia nigra pars reticulata and the internal segment of the globus pallidus (GPi), which then project to the thalamus. Because the striatonigral / striatoentopeduncular and nigrothalamic pathways are inhibitory, activation of the direct pathway