The basal ganglia, interconnected brain areas within the cerebral cortex, were originally thought to involve motor control. These nuclei have since been proven to affect learning and focus, form good and bad habits, and contribute to addictive disorders. The inhibitory neurotransmitter GABA plays the most important role in the basal ganglia.
The largest nuclei group, the corpus striatum, includes the caudate nucleus, putamen, globus pallidus, and nucleus accumbens. The caudate sends messages to the frontal lobe (particularly the orbital cortex), and seems responsible for informing us that something is wrong and needs correction. An overactive caudate may result in obsessive compulsive disorder (OCD).
Problems with Overactive Basal Ganglia
“Disturbances involving the neural circuits between the cortex and basal ganglia, similar to those found in patients with OCD, may also be present in anorexic patients,” says Dr. Paolo Cavedini, a psychiatrist in Milan. A recent positron emission tomography (PET) study showed overactive dopamine receptors in the basal ganglia of anorexic patients. Such overactivity may result in obsessive feelings about food as well as rewardlike releases from the neurotransmitter dopamine during starving behaviors. Dopamine surges may perpetuate those behaviors into habit.
Effects of Inactive Caudate
If the caudate is inactive, various disorders such as ADD, ADHD, schizophrenia aspects, depression, and lethargy may result. Caudate nucleus damage may result in PAP (or Athymhormic) syndrome, wherein one experiences an ususual lack of motivation. One extreme example is non-motivation to save one’s own life!
Putamen and Basal Ganglia
The putamen, under and behind the front of the caudate, appears to affect automatic behaviors such as driving or bike riding. Problems in this area may result in Tourette’s symptoms. The globus pallidus receives inputs from the caudate and putamen and provides outputs to the substantia nigra. The accumbens receives signals from the prefrontal cortex and returns them via the globus pallidus. The pars compacta in the substantia nigra uses dopamine neurons to signal the striatum, which may involve reward circuits. The pars reticulata controls eye movements and may affect Parkinson’s and epilepsy. Huntington’s disease, cerebral palsy, dystonia, and hemiballismus (uncontrollable movement on one side of the body) are thought to be other conditions of this dysfunction.
Treatment for Basal Ganglia Dysfunction
While basal ganglia dysfunction can have severe consequences, treatment plans offer hope to those who suffer from such disorders. Several methods have been effective.
Gene therapy, in its infancy but promising, replaces diseased phenotypes with new genetic material. This treatment appears viable for neurodegenerative disorders. One example is implanting genetically modified cells that convert to dopamine.
Lesioning destroys neuronal cells in a particular area. Ablation can be likened to removing a faulty piece of a circuit. When this occurs, the healthy area of the circuit functions normally.
Deep brain stimulation inserts electrodes that emit high-frequency stimulation to the implanted areas in the brain’s sensorimotor area. Adjusting stimulation protocols, thereby altering the activity of basal ganglia circuits, lends this treatment to a variety of disorders.