Discourse studies in neurologically impaired populations: a quest for action.

Organism and environment are in a state of constant interaction, and discourse is viewed as one form of manifestation of this interaction. Through the study of discourse insights can be gained into those components that bring about mental events. Verbal structure, communication of beliefs and action/interaction are highly interactive dimensions of discourse. Taking this perspective as a framework, the findings of discourse studies with a particular emphasis on right-hemisphere brain-damaged individuals are discussed. Neurolinguistic studies of discourse can be divided into four categories: (1) studies that focus primarily at providing a detailed description of the structural and interactional abilities of brain-damaged individuals, (2) studies that are mainly concerned with investigating the processing aspects of discourse, (3) studies that investigate the influence of cognitive systems such as attention or memory on discourse processing, and (4) studies that try to relate discourse processing mechanisms to underlying biological substrates or neurophysiological mechanisms. A quest is made for future research to base discourse studies on well-defined processing theories, to include different processing components and levels, and to systematically investigate the impact of facets of cognitive systems on such processing. Established methodological approaches should be complemented by electrophysiological procedures (such as the event related potentials technique) or functional imaging techniques (such as fMRI) to tackle relationships between discourse processing mechanisms, cognitive systems and underlying biological mechanisms. Consideration of the influence of biochemical processes (such as asymmetries of neurotransmitters, endocrine functions, or influence of pharmacological agents) on component processes may add to our insights.