Introduction

Olfactory deficits are found in neurodegenerative disorders, predominantly in later life, as well as in disorders with an onset in childhood or adolescence. The former will be considered in detail in Chapters 14–16. It is clear that the neuropathological changes accompanying neurodegenerative disorders are implicated in causing such deficits in olfactory abilities. In contrast, the processes underlying olfactory abnormalities in disorders of early development are less clear and are best understood in the context of dynamic brain maturational changes that are occurring at this time. Thus, neurobiology relevant to the deficits observed in disorders having a neurodevelopmental basis, such as the autistic spectrum disorders, attention deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD) and schizophrenia, may relate more to abnormalities in the processes of brain maturation rather than to specific neuropathological processes, or to an interaction between brain maturation and other processes relevant to these conditions.

We suggest that in order to understand the nature of the deficits observed in various aspects of olfactory function in early developmental disorders, it is important to consider the nature of the normal brain structural and functional changes that are occurring at the time of their onset. It is likely that interruption of these normal processes by the emergence of such disorders at critical times of maturation adversely affect the development of olfactory functions. Interruption of normal neurodevelopment, reflected by olfactory deficits, may manifest as developmental arrest, developmental lag or possibly functional deterioration following onset of these conditions.