Introduction

The Dual Route Cascaded model proposes that reading is accomplished by a left dorsal (occipito-parieto-frontal) pathway and a left ventral (occipito-temporo-parietal) pathway. The former route is specialized in reading nonwords and regular words utilizing grapheme-to-phoneme conversion rules, the latter processes familiar regular and irregular words by activating semantic and lexical orthographic representations. With this framework in mind, we investigated the cognitive and metabolic correlates of the ability to read single words and nonwords in mild dementia of the Alzheimer type (DAT).

Methods

We assessed the ability to read words (high-frequency concrete, low-frequency concrete, low-frequency abstract and function words) and nonwords in 25 mild DAT patients and 25 elderly healthy participants. Patients’ reading performance was correlated with scores on an extensive array of cognitive tests and, in 21 cases, with distribution of brain metabolism on FDG-PET using SPM8.

Results

Patients’ reading scores did not differ from healthy controls’ scores. Regression analysis identified the Pyramid and Palm Trees test and Letter Span as predictors of reading ability.

Clusters of hypometabolism correlated with poorer reading were found in the left angular and pre-central gyri for words+nonwords, in the left angular gyrus for words, in the left>right pre-central cortex and anterior cingulate cortex for nonwords.

Conclusions

As expected, mild DAT patients showed preserved ability to read. Behavioral and metabolic imaging analyses converged in highlighting an involvement of semantics, mapped to the angular gyrus, phonological processing, mapped to the posterior frontal cortex, and attention, mapped to the anterior cingulate cortex, in the ability to read, in these patients.