Functionally distinct contributions of the anterior and posterior putamen during sublexical and lexical reading

Marion Oberhuber,‘Ōiwi Parker Jones,Susan Prejawa,Cathy J Price,Mohamed L Seghier,David W Green,Thomas M H Hope

doi:10.3389/fnhum.2013.00787

Abstract

Previous studies have investigated orthographic-to-phonological mapping during reading by comparing brain activation for (1) reading words to object naming, or (2) reading pseudowords (e.g., “phume”) to words (e.g., “plume”). Here we combined both approaches to provide new insights into the underlying neural mechanisms. In fMRI data from 25 healthy adult readers, we first identified activation that was greater for reading words and pseudowords relative to picture and color naming. The most significant effect was observed in the left putamen, extending to both anterior and posterior borders. Second, consistent with previous studies, we show that both the anterior and posterior putamen are involved in articulating speech with greater activation during our overt speech production tasks (reading, repetition, object naming, and color naming) than silent one-back-matching on the same stimuli. Third, we compared putamen activation for words versus pseudowords during overt reading and auditory repetition. This revealed that the anterior putamen was most activated by reading pseudowords, whereas the posterior putamen was most activated by words irrespective of whether the task was reading words or auditory word repetition. The pseudoword effect in the anterior putamen is consistent with prior studies that associated this region with the initiation of novel sequences of movements. In contrast, the heightened word response in the posterior putamen is consistent with other studies that associated this region with “memory guided movement.” Our results illustrate how the functional dissociation between the anterior and posterior putamen supports sublexical and lexical processing during reading.

Highlights

Reading involves the mapping of visual features to meaning and to articulatory codes that will generate the corresponding speech sounds
FMRI RESULTS Areas activated by reading more than naming Our areas of interest were defined as those that were more activated for reading words and pseudowords compared to object and color naming
Greater activation for words than pseudowords was observed in the posterior putamen with no significant interaction between stimulus type and task; see Table 1

Summary

Introduction

Reading involves the mapping of visual features (orthography) to meaning (semantics) and to articulatory codes (phonology) that will generate the corresponding speech sounds (phonetics). The non-semantic mapping from orthography-to-phonology can theoretically proceed lexically or sublexically (i.e., “champion” versus “cham”-“pi”-“on”), with sublexical processing enabling new or low frequency words (e.g., “jentacular”) to be read. The aim of our paper was to identify the brain areas associated with non-semantic orthographic-to-phonological mapping. We start by considering the cognitive processing that might be needed to support this function. There are multiple levels at which orthography can be mapped to phonology within a single word. The different levels are more or less consistent (e.g., the letter “m” has a similar sound by itself as in the word “champ”), there will be multiple levels of inconsistencies, in non-transparent languages like English (e.g., “c” has a different sound by itself than in “ch”). Sublexical phonological codes need to be assembled in the right order with the correct prosody prior to speech production

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