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Located in the center of the brain, within the basal ganglia, is a structure called the lentiform nucleus, which consists of small groups of brain cells called neurons. Sometimes, this structure is referred to as the lenticular nucleus. It includes two components — the globus pallidus and the putamen — and assists the cerebellum in coordinating small, precise muscle movements.
The globus pallidus seems to play a role in maintaining muscle tone throughout the body. Damage to this region can result in a condition known as dystonia, where muscles can lose their tone and have difficulties executing commands sent to them from the brain. Studies using a technique called deep-brain stimulation, which uses surgery to allow for electrical stimulation of the globus pallidus, has shown some ability to reverse this damage. Patients undergoing this procedure showed improvement in muscle movement in the head, face, and trunk, and did not experience further muscle degeneration. This study demonstrates the importance of this structure in regulating muscle conditions and movements for a large part of the body.
The other structure that comprises part of the lentiform nucleus, the putamen, also serves to coordinate a wide range of movement-related functions. Many brain structures have nerve connections to the area, which contribute to these functions. Studies have shown that cells in the putamen help to determine the direction of muscle movements, particularly in the limbs. These particular cells seem to be more involved in coordinating the purpose of movements, rather than activating individual muscles to carry out these movements.
Other studies have revealed additional roles of the cells in the putamen. Procedural memory, which governs the memorization of muscle activities to perform tasks, is another important function of this structure. Injections of a drug that temporarily inhibits neuronal activity was found to cause difficulties in memorizing button-pushing tasks in a study involving monkeys. Some repetition of learned movements that occurs during Parkinson's disease is thought to be related to damage to the region, as well.
Learning that occurs from unconscious integration of stimuli into memory is another role of the lentiform nucleus. Damage to parts of the putamen can cause difficulties in tasks that require the acquisition of knowledge from repeated tasks. These individuals are still able to learn by consciously memorizing certain rules related to the task, however, showing that declarative memory involving facts and conscious studying is not affected.
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