In part because of their striking clinical presentations, disorders of higher nervous system function figured prominently in the early history of neurology. These disorders are not merely historical curiosities, however. As apraxia, neglect, and agnosia have important clinical implications, it is important to possess a working knowledge of the conditions and how to identify them.
Apraxia is a disorder of skilled action that is frequently observed in the setting of dominant hemisphere pathology, whether from stroke or neurodegenerative disorders. In contrast to some previous teaching, apraxia has clear clinical relevance as it is associated with poor recovery from stroke. Neglect is a complex disorder with many different manifestations that may have different underlying mechanisms. Neglect is, in the author’s view, a multicomponent disorder in which impairment in attention and arousal is a major contributor. Finally, agnosias come in a wide variety of forms, reflecting impairments ranging from low-level sensory processing to access to stored knowledge of the world (semantics).
The classic behavioral disorders reviewed here were of immense interest to early neurologists because of their arresting clinical phenomenology; more recent investigations have done much to advance the neuroscientific understanding of the disorders and to reveal their clinical relevance.