Differing neuropsychological and neuroanatomical correlates of abnormal reading in early-stage semantic dementia and dementia of the Alzheimer type.

Individuals with semantic dementia (SD) were differentiated neuropsychologically from individuals with dementia of the Alzheimer type (DAT) at very mild-to-mild stages (clinical dementia rating 0.5 or 1). A picture naming and recognition memory experiment provided a particularly useful probe for early identification, with SD individuals showing preserved picture recognition memory and impaired naming, and DAT individuals tending to show the reverse dissociation. The identification of an early SD group provided the opportunity to inform models of reading by exploring the influence of isolated lexical semantic impairment on reading regular words. Results demonstrated prolonged latency in both SD and DAT group reading compared to a control group but exaggerated influence of frequency and length only for the SD group. The SD reading pattern was associated with focal atrophy of the left temporal pole. These cognitive-neuroanatomical findings suggest a role for the left temporal pole in lexical/semantic components of reading and demonstrate that cortical thickness differences in the left temporal pole correlate with prolonged latency associated with increased reliance on sublexical components of reading.

Common and dissociable activation patterns associated with controlled semantic and phonological processing: evidence from FMRI adaptation.

Recent evidence suggests specialization of anterior left inferior prefrontal cortex (aLIPC; approximately BA 45/47) for controlled semantics and of posterior LIPC (pLIPC; approximately BA 44/6) for controlled phonology. However, the more automated phonological tasks commonly used raise the possibility that some of the typically extensive aLIPC activation during semantic tasks may relate to controlled language processing beyond the semantic domain. In the present study, an event-related fMRI adaptation paradigm was employed that used a standard controlled semantic task and a phonological task that also emphasized controlled processing. When compared with letter (baseline) processing, significant fMRI task and adaptation effects in the aLIPC and pLIPC regions ( approximately BA 45/47, approximately BA 44) were observed during both semantic and phonological processing, with aLIPC showing the strongest effects during semantic processing. A left frontal region ( approximately BA 6) showed task and relative adaptation effects preferential for phonological processing, and a left temporal region ( approximately BA 21) showed task and relative adaptation effects preferential for semantic processing. Our results demonstrate that aLIPC and pLIPC regions are involved in controlled processing across multiple language domains, arguing against a domain-specific LIPC model and for domain-preferentiality in left posterior frontal and temporal regions.