Brain networks for reading in stroke alexia and typical aging

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ABSTRACT Our active grant, Brain Networks for Reading in Stroke Alexia and Typical Aging, is designed to examine the brain and cognitive bases of reading. This supplemental project employs the techniques already in place in the parent grant to examine the neurocognitive basis of reading decline in people with primary progressive aphasia (PPA), a disorder most commonly associated with frontotemporal dementia or Alzheimer’s disease. The ability to read is fundamental to living in modern society. Loss of reading ability due to stroke, head injury, or dementia, called alexia, affects millions of Americans at any given time and causes difficulty performing many daily life functions. To improve diagnosis and treatment of alexia, we must understand the neurocognitive basis of reading. In the parent grant we are conducting a large study of both stroke alexia and typical reading in older adults, using detailed measures of reading ability and the most advanced multimodal neuroimaging methods available. Reading relies on brain networks that evolved for speech and language processes, but neurocognitive models of reading have not yet incorporated recent advances in our understanding of these networks. The parent grant proposes a new model of Reading Integrated with Speech and Semantics (RISS) that provides a more specific neurocognitive architecture for reading than prior models. The RISS model articulates the important role that semantics must play in reading. Semantic processing is hypothesized to rely heavily on activation of the left anterior temporal lobe (ATL). However, it is difficult to examine the ATL using BOLD fMRI in neurotypical adults due to its close proximity to the sinuses; and the ATL is rarely damaged by stroke. A significant advantage of studying reading in people with primary progressive aphasia is that this population includes people whose atrophy is largely focused in the anterior temporal lobe of the left hemisphere. In fact, a particular pattern of alexia, called surface alexia, has been linked to a particular variant of PPA, semantic variant PPA (svPPA). Atrophy in svPPA tends to be focused in the ATL. Yet it is important to note that patterns of alexia, including surface alexia, can be seen in all variants of PPA, with atrophy observed in other regions of the left hemisphere. Combining results from this supplement with results from the parent study, then, will provide a more global perspective of how reading is represented in the brain. The past decade has seen an increase in the number of studies designed to develop treatments for language impairments in dementia. Most of these studies target word finding impairments, and some focus on increasing fluency. Reading impairments in dementia have received little attention. By advancing our understanding of the neurocognitive basis of alexia in dementia, this project will pave the way for developing effective treatments for alexia in stroke and in dementia.