Background & Significance: Impaired function of the prefrontal cortex (PFC) is a common occurrence following traumatic brain injury (TBI). These changes are reflected behaviorally in the disruption of cognitive process that are necessary to support complex and naturalistic communication in one of the many forms of discourse (e.g., conversation, description, narrative, etc.). Discourse is a commonly occurring and cognitively demanding form of communication that relies on an interaction of cognitive (e.g., executive functions necessary to guide the goal-directed information exchange) and linguistic components. Because of the prevalence and importance of discourse in daily routines (educational, vocational, family, social), disrupted discourse is an important target for rehabilitative treatment for persons with cognitive-communication impairments (CCI) associated with TBI (American Speech-Language Hearing Association [ASHA], 2005). However, there is a paucity of information about the underlying “cognitive architecture” and processing demands that support various forms of discourse. This is in part due to methodological constraints of many neuroimaging technologies (e.g., fMRI) that severely limit ecologically typical communication acts such as listening and speaking during neuroimaging. To overcome these limitations, functional near infrared spectroscopy (fNIRS) can be used to identify patterns of neural activity by monitoring hemodynamic activity related to the production of discourse during natural speaking situations. 

Methods: Eleven neurologically healthy adults formulated procedural discourse, personal narrative (recount), fictional narrative, and conversation. On microstructural behavioral measure (efficiency) and one macrostructural measure (informativeness) were measured from each genre using established clinically relevant protocols, and prefrontal neurovascular activation was measured using functional near infrared spectroscopy (fNIRS). 

Results: Efficiency was similar between the four genres. There were significant differences in informativeness between high and low complexity procedural discourse, and between fictional narrative and conversation. Informativeness was highest in conversation and lowest in complex procedural discourse. Neurovascular activity was highest for the high emotional intensity personal narrative. There was significant negative correlation between fictional narrative informativeness and neurovascular activation. Generally, there was a negative association between discourse efficiency and neurovascular activation. 

Conclusion: The findings suggest that measurement of efficiency enables meaningful comparison of discourse across genres. Procedural, personal, and conversation discourse are formulated with lower efficiency than fictional narratives. Processing demands (PFC) and communicative efficiency should be considered in treating CCI. Training discourse structure and support strategies for persons with cognitive-communication impairments should use a hierarchical approach based on genre. Exploration of ecologically relevant genres of discourse is feasible and relevant for individuals with cognitive-communication impairments and SLPs planning treatment interventions for persons with CCI.

Discourse Formulation and Neurovascular Activation: Implications for Treating Cognitive Communication Disorders