The neuroscience of action semantics in neurodegenerative brain diseases.

PURPOSE OF REVIEW: Within the last decade, the neurobiology of action processing has moved from an obscure topic of specialist interest to one of the most popular themes in modern neuroscience. However, the wealth of literature and the diversity of approaches and theoretical models can make the field complex and, at times, bewildering. This review presents the main currents of research, examining their theoretical underpinnings in an interdisciplinary context. RECENT FINDINGS: The presence of specific deficits in verb and action processing has been documented in a wide range of neurodegenerative diseases, including parkinsonian syndromes and motor neuron disease. Interestingly, most of these disorders affect the motor system, suggesting a systematic relationship between motor functions and their cognitive and linguistic representations. Action processing has been explored with a whole spectrum of methodologies, from neuroimaging to transcranial and intracranial stimulation. The findings have been integrated with other influential concepts and theories, including mirror neurons and embodied cognition. SUMMARY: Converging evidence from patient and imaging studies links the concepts of actions and their processing with the execution of actions through the motor system. The theory of embodied cognition remains influential as well as controversial. However, the points of criticism have changed, reflecting recent paradigm shifts.