"Our brain can construct language, music and mathematics, but the same brain also lets us develop habits of thought and action. These semi-automatic routines free us to think and to attend to the world. Getting the right balance of what we do with conscious effort and what we do seemingly effortlessly by habit is part of the role of the basal ganglia, deep structures in the forebrain that interact with the neocortex above. The striatum, the main input structure of the basal ganglia, is responsible for much of what we call habit learning. Moreover, the striatum is centrally implicated in human neurologic and neuropsychiatric disorders. These range from problems that affect the motor system, as in Parkinson’s disease, to problems that affect cognition and emotion and action control, as in obsessive-compulsive disorder, Tourette syndrome, depression and states of addiction. Imbalances in neurotransmitters in the striatum are now known to be important both for the normal functions of cortico-basal ganglia circuits and for the development of disordered functions in basal ganglia-based disorders.
This image illustrates a thin slice through the striatum of the human brain stained with a molecular stain that shows in white the distribution of one of the most important neurotransmitter systems in the basal ganglia, acetylcholine. Within the large white zones there are small gray zones of lower cholinergic staining. These are the striosomes (striatal bodies) that are thought to function in integrating emotional and cognitive signals with sensorimotor signals in the striatum. It is now thought that a balance between the striosomes and the extrastriosomal matrix is critically important in the balance between repeating the same action or choosing another action, and that disruption of this balance may contribute to dysfunction in basal-ganglia based neurologic and neuropsychiatric disorders. The jet black zone that cuts into the white-stained striatum is not the striatum, but the large bundle of fibers that interconnect the neocortex with the striatum and other sites. Striosomes were first identified in the human brain in 1978 by the Graybiel Laboratory at MIT.
MIT is a cauldron of discovery in many fields, and in recent years MIT has become a leader in the new field of neuroscience. The goal of this field is to understand brain and mind at levels ranging from the molecular to the cognitive, and to use this knowledge in translational work to help individuals with brain disorders. This image illustrates a neurochemical organization of the human forebrain that was discovered at MIT and that is increasingly being found important in the analysis of the brain in neurologic and neuropsychiatric conditions.
The image comes from Graybiel, A.M. (1984) Neurochemically specified subsystems in the basal ganglia. In: Functions of the basal ganglia, D. Evered and M. O'Connor, Eds. London: Pitman, pp. 114-149.