Unlike the thalamus, which has broad reciprocal connectivity, cortical projections with the putamen are afferent, thus sending information as opposed to receiving it. Cortical communication is accomplished via multi-fiber pathways as outlined previously (i.e. via other subcortical structures). Dopamine Dopamine is a neurotransmitter that has a dominant role in the putamen, most of it is supplied from the substantia nigra. When a cell body of a neuron (in the putamen or caudate nuclei) fires an action potential, dopamine is released from the presynaptic terminal. Since projections from the putamen and caudate nuclei modulate the dendrites of the substantia nigra, the dopamine influences the substantia nigra, which affects motor planning. This same mechanism is involved in drug addiction. In order to control the amount of dopamine in the synaptic cleft, and the amount of dopamine binding to post synaptic terminals, presynaptic dopaminergic neurons function to reuptake the excess dopamine. Other neurotransmitters The putamen also plays a role in modulation of other neurotransmitters. It releases GABA, enkephalin, substance P, and acetylcholine. It receives serotonin and glutamate. Function: motor skills The putamen is interconnected with many other structures, and works in conjunction with them to influence many types of motor behaviors. These include motor planning, learning, and execution, motor preparation, specifying amplitudes of movement, and movement sequences. Some neurologists hypothesize that the putamen also plays a role in the selection of movement (e.g. Tourette syndrome) and the "automatic" performance of previously learned movements (e.g. Parkinson's disease). In one study it was found that the putamen controls limb movement. The goal of this study was to determine whether particular cell activity in the putamen of primates was related to the direction of limb movement or to the underlying pattern of muscular activity. Two monkeys were trained to perform tasks that involved the movement of loads. The tasks were created so that movement could be distinguished from muscle activity. Neurons in the putamen were selected for monitoring only if they were related both to the task and to arm movements outside the task. It was shown that 50% of the neurons that were monitored were related to the direction of movement, independent of the load. Another study was done to investigate movement extent and speed using PET mapping of regional cerebral blood flow in 13 humans. Movement tasks were performed with a joystick-controlled cursor. Statistical tests were done to calculate the extent of movements and