The overlap of speech production and verbal working memory

Abstract To enable the expression of ideas in everyday conversation, our brain must hold on to speech information for short periods of time in verbal working memory (vWM). This is particularly important for everyday conversation that takes place in chaotic environments: Plans for speaking change quickly, and the brain has to adapt to these changes. Previous models of vWM, have suggested that vWM is anatomically and functionally discrete, with only indirect interactions with speech production. Evidence from lesions following strokes however, have shown a wide range of speech production deficits that are also associated with problems with vWM, arguing against a strong dissociation between speech production and vWM. We propose instead that vWM is integrated in the speech production planning system, sharing an anatomical and functional substrate. To study this overlap, we propose to examine neural responses associated with this functional overlap through a population of neurosurgical patients who as part of their clinical care have electrodes implanted directly in their brain, giving us a unique opportunity to study the human brain at a greater resolution that has been done in the past. We will leverage this access to address the following questions: 1) Does speech production and vWM overlap in the brain? 2) What kind of information is held when planning for speech production? 3) What motor features are shared between speech production and vWM? We will use a series of tasks that are designed to separate out the role of vWM for different speech production components and measure human brain responses using direct brain recordings, including high density electrodes that have unprecedented spatial resolution (<1 mm, up to 1024 electrodes for a 10 x increase in sampling). Understanding this basic cognitive process and their role in everyday language use will lead to more targeted approaches to help the over 1 million Americans who suffer from stroke-induced aphasia.