Studying cognitive functions by means of direct electrical stimulation: a review.

In recent years, neurosurgical patients have highly contributed to research in behavioural neurology. This development is in part due to the use of direct electrical stimulation during brain surgery. Indeed, during surgery for a tumour, involving both grey and white matter, it has become a common clinical practice to awaken patients with the aim of investigating the functional role of restricted brain areas. The surgeon can optimize the extent of resection and improve overall survival without causing permanent neurological deficits, owing to individual, specific mapping and preservation of eloquent structures. This type of mapping offers a unique opportunity to investigate the functional connectivity of the brain, permitting real-time anatomo-functional correlations, in awaken patients undergoing surgery. By gathering all cortical and axonal sites in which stimulation produces the same types of error, one can build up a picture of the network underlying the disrupted function. In this review, the main achievements concerning networks involved in some aspects of language, visuo-spatial cognition, calculation and emotion will be highlighted.