Neuroimaging studies of word reading

Neuroimaging studies of word reading

Julie A. Fiez*,† and
Steven E. Petersen‡

^*Department of Psychology, University of Pittsburgh and the Center for the Neural Basis of Cognition, University of Pittsburgh/Carnegie Mellon University, Pittsburgh, PA 15260; and ^‡Departments of Neurology and Neurological Surgery, Anatomy and Neurobiology, Radiology, Washington University School of Medicine, St. Louis, MO 63110

Abstract

This review discusses how neuroimaging can contribute to our understanding of a fundamental aspect of skilled reading: the ability to pronounce a visually presented word. One contribution of neuroimaging is that it provides a tool for localizing brain regions that are active during word reading. To assess the extent to which similar results are obtained across studies, a quantitative review of nine neuroimaging investigations of word reading was conducted. Across these studies, the results converge to reveal a set of areas active during word reading, including left-lateralized regions in occipital and occipitotemporal cortex, the left frontal operculum, bilateral regions within the cerebellum, primary motor cortex, and the superior and middle temporal cortex, and medial regions in the supplementary motor area and anterior cingulate. Beyond localization, the challenge is to use neuroimaging as a tool for understanding how reading is accomplished. Central to this challenge will be the integration of neuroimaging results with information from other methodologies. To illustrate this point, this review will highlight the importance of spelling-to-sound consistency in the transformation from orthographic (word form) to phonological (word sound) representations, and then explore results from three neuroimaging studies in which the spelling-to-sound consistency of the stimuli was deliberately varied. Emphasis is placed on the pattern of activation observed within the left frontal cortex, because the results provide an example of the issues and benefits involved in relating neuroimaging results to behavioral results in normal and brain damaged subjects, and to theoretical models of reading.

Footnotes

↵ † To whom reprint requests should be addressed at: 605 LRDC, 3939 O’Hara Street, Department of Psychology, University of Pittsburgh, Pittsburgh, PA 15260. e-mail: fiez+{at}pitt.edu.
This paper was presented at a colloquium entitled “Neuroimaging of Human Brain Function,” organized by Michael Posner and Marcus E. Raichle, held May 29–31, 1997, sponsored by the National Academy of Sciences at the Arnold and Mabel Beckman Center in Irvine, CA.
↵ § All neuroimaging studies of reading that met the following criteria were included in this analysis: (i) subjects read aloud a series of individually displayed words, (ii) data were compared with a relatively passive or sensorimotor control condition (see text for further description), (iii) the majority of the brain was imaged, and (iv) regions of activation were reported as coordinate locations (foci) in terms of the Talairach and Tournoux atlas space (10). In all nine studies that met these criteria, the data were acquired by using PET.
↵ ¶ In several of the studies word reading was compared with different control conditions, or different task variations were compared with the same control condition. In such studies, activation of the same region often was found in multiple comparisons. As an alternative to dealing with each focus separately, or arbitrarily selecting only one comparison to evaluate, similarly located foci within an individual study were averaged together.
↵ ‖ A focus from any given study was judged to represent commonly found activation if it was near (within 20 mm) foci from a majority of studies. In other words, each focus had to be near a focus from at least four of the other eight studies, or near a focus from at least three of the six studies that used a passive control condition (to avoid excluding areas involved in visual processing and speech production). The 20-mm distance criterion was chosen because it is near the resolution of most analyzed PET images, and it is beyond the range of the typical response variability found between subjects and studies.
↵ ** Foci were assigned to clusters based on the Brodmann area (BA)/gyral location to which each focus plotted. In some cases, more than one focus from a given study fell within the same Brodmann region. When this tendency appeared across studies, the foci were divided into two clusters (e.g., in many of the studies both a dorsal and a more ventral focus were identified within BA 4). Finally, the mean location of the foci falling within each cluster was computed.
ABBREVIATIONS:

BA,

Brodmann area;

SMA,

supplementary motor area;

PET,

positron emission tomography