Disconnecting cognition.

PURPOSE OF REVIEW: The aim is to assess whether the recent surge in brain 'connectivity' studies has improved our understanding of neurological deficits and in particular so-called disconnection syndromes.

RECENT FINDINGS: Across a large variety of brain diseases, functional connectivity measures obtained from 'resting state' studies show alterations in distributed neural networks that may be of explanatory value for disease severity. In parallel, studies of structural connectivity reveal how damage to identified fiber tracts can yield specific clinical symptoms. These methods are not only permitting testing of the disconnection mechanism in the few syndromes where it has classically been suspected, but also starting to propose disconnection accounts for other syndromes that have not been conceptualized this way before. Finally, both structural and functional connectivity studies contribute to improve the mechanistic understanding of cognitive deficits in disseminated white matter disease.

SUMMARY: In many respects, studies of structural and functional connectivity using MRI are providing critical novel empirical evidence for--and also against--disconnection as the relevant pathomechanism in neurological syndromes. At the same time, the observation of altered long-range correlation of activity in a wide variety of brain diseases may also be overinterpreted as disconnection, which dilutes an originally rather specific understanding of this concept.