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2. BRAIN MECHANISMS: NEUROBIOLOGY AND NEUROANATOMY

CHAPTER 2

Brain Mechanisms: Neurobiology

and Neuroanatomy

Introduction
Substance dependence is a disorder that involves the motivational systems
of the brain. As with any disorder specific to an organ or system, one must
first understand the normal function of that organ or system to understand
its dysfunction. Because the output of the brain is behaviour and thoughts,
disorders of the brain can result in highly complex behavioural symptoms.
The brain can suffer many types of disease and traumas, from neurological
conditions such as stroke and epilepsy, to neurodegenerative diseases such
as Parkinson disease and Alzheimer disease, to infections or traumatic brain
injuries. In each of these cases, the behavioural output is recognized as being
part of the disorder.
Similarly, with dependence, the behavioural output is complex, but is
mostly related to the effects of drugs on the brain. The tremors of Parkinson
disease, the seizures of epilepsy, even the melancholy of depression are widely
recognized and accepted as symptoms of an underlying brain pathology.
Dependence has not previously been recognized as a disorder of the brain,
in the same way that psychiatric and mental illnesses were not previously
viewed as being a result of a disorder of the brain. However, with recent
advances in neuroscience, it is clear that dependence is as much a disorder
of the brain as any other neurological or psychiatric illness. New technologies
and research provide a means to visualize and measure changes in brain
function from the molecular and cellular levels to changes in complex
cognitive processes, that occur with short-term and long-term substance use.
This chapter reviews basic principles of brain anatomy and function to
provide a framework within which the neuroscience of dependence can be
discussed.

Organization of the brain

The nervous system is the body’s major communication system, and is
divided into central and peripheral regions. The central nervous system
consists of the brain and spinal cord, and the peripheral nervous system
consists of all nerves outside of this. The spinal cord controls reflex actions,
and relays sensory and motor information between the body and the brain,
so that the organism can respond appropriately to its environment.

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