Neuroanatomical correlates of category-specific semantic disorders: a critical survey

Previous studies of category-specific semantic disturbances have focused their attention on the intrinsic cognitive structure of these disorders. The present survey aims to evaluate the relationships between disrupted semantic category and localisation of the underlying brain damage, in order to establish whether the injured brain areas house just those neurophysiological mechanisms that should have critically contributed to the acquisition of the disrupted semantic categories. We took into account in our review two double dissociations concerning respectively: (1) the impairment of a specific linguistic category--we contrast those disorders selectively affecting verbs (action names) with those selectively affecting nouns (object names); (2) the impairment of a specific conceptual/semantic domain--we contrast disorders selectively affecting living beings with those preferentially affecting man-made artefacts. The hypothesis that different categories of knowledge may be closely intertwined with different sources of sensory-motor information, was substantially confirmed. The lesion preferentially encroached on the left frontal lobe when the category "verbs" was selectively affected; it involved the left temporal lobe and the posterior association areas when the category "nouns" was preferentially disrupted; it involved bilateral temporo-limbic structures and inferior temporal lobes when the category "living beings" was selectively disrupted; it usually encroached on the left fronto-parietal areas when man-made artefacts and body parts were preferentially affected. These data support the hypothesis that: (a) action schemata may critically contribute to the development of the semantic representation of verbs, (b) mechanisms of sensory integration may play an important role in establishing the semantic representation of nouns; (c) high-level visual processing and multi-modal sensory convergency may critically contribute to organising the semantic representation of living beings; (d) motor-kinaesthetic integration may play a leading role in developing the semantic representation of man-made artefacts.