Mirror neurons and their relationship with neurodegenerative disorders.

The finding of mirror neurons (MNs) has provided a biological substrate to a new concept of cognition, relating data on actions and perceptions not only to integrate perception in action planning and execution but also as a neural mechanism supporting a wide range of cognitive functions. Here we first summarize data on MN localization and role in primates, then we report findings in normal human subjects: functional magnetic resonance imaging and neurophysiological studies sustain that MNs have a role in motor learning and recognizing actions and intentions of others, and they also support an embodied view of language, empathy, and memory. Then, we detail the results of literature searching on MNs and embodied cognition in Parkinson's disease (PD), frontotemporal dementia (FTD)/amyotrophic lateral sclerosis (ALS), and in mild cognitive impairment (MCI)/Alzheimer's disease (AD). In PD the network of MN could be altered, but its hyperactivation might support motor and cognitive performances at least in early stages. In the ALS/FTD continuum, preliminary evidence points out to an involvement of the MN network, which could explain language and inter-subjectivity deficits shown in patients affected by these clinical entities. In the MCI/AD spectrum, a few recent studies suggest a possible progressive involvement from posterior to anterior areas of the MN network, with the brain putting in place compensatory mechanisms in early stages. Reinterpreting neurodegenerative diseases at the light of the new views about brain organization stemming from the discovery of MN could help to better comprehend clinical manifestations and open new pathways to rehabilitation.