Chapter 23 - Agnosias, apraxias, and callosal disconnection syndromes

Summary

Various kinds of agnosia may affect each perceptual modality (e.g. visual, auditory, or tactile). This chapter provides an overview of their manifestations, clinical assessment, and cerebral localization. Transformation agnosia is a deficit involving a particular inability to extract a 3D representation of objects seen from unusual perspectives or unusual lighting, while recognition is preserved for prototypical 2D views. Pure alexia as well as difficulties in color and face recognition are often associated. Three main subtypes of apraxia disorders described are limb gestures, orofacial gestures, and wholebody gestures, each with different degrees of difficulties. Orofacial apraxia is accompanied by nonfluent aphasia and ideomotor limb apraxia. Callosal disconnection signs result from an interruption of these fibers by damage to the corpus callosum itself or adjacent white matter. These signs reflect the fact that each hemisphere receives only contralateral sensory inputs and controls only contralateral motor output, but also has specialized processing capacities.