Brain circuitry

This diagram illustrates the principle that brain circuits travel up and down the neuroaxis, from one side of the brain to the other, as well as back and forth between many different brain components at several levels within the forebrain, thalamus, hypothalamus, midbrain, medulla, cerebellum and spinal cord.
Why is it important to learn how brains are constructed?
For a brain to perform all the functions that it must do, it must: 1. Detect and locate the great variety of stimulus types, sources, and happenings in the environment; 2. Make sense of all these sensory events; 3. Respond to all these features by expressing an elaborate behavioral repertoire; and 4. Make judgments, learn, and think about all these things.
Over the last 50 years, a great number of neuronal cell groups, circuits and connections have been identified and named in the several different regions of the brain. In addition, the functions of these different nuclei and circuits have been identified. Moreover, the neuroanatomical and neurochemical mechanisms by which these circuits operated to produce and enable them to function effectively have begun to be clarified. But much remains to be done, and in the next two decades, it is estimated that modern technology will provide ever greater insight as to how the circuits of the brain perform the functions that they do.