The cerebellum's role in reading: a functional MR imaging study

Abstract

Background and purpose: Long considered to have a role limited largely to motor-related functions, the cerebellum has recently been implicated as being involved in both perceptual and cognitive processes. Our purpose was to determine whether cerebellar activation occurs during cognitive tasks that differentially engage the component processes of word identification in reading.

Methods: Forty-two neurologically normal adults underwent functional MR imaging of the cerebellum with a gradient-echo echo-planar technique while performing tasks designed to study the cognitive processing used in reading. A standard levels-of-processing paradigm was used. Participants were asked to determine whether pairs of words were written in the same case (orthographic processing), whether pairs of words and non-words rhymed with each other, respectively (phonologic assembly), and whether pairs of words belonged to the same category (semantic processing). Composite maps were generated from a general linear model based on a randomization of statistical parametric maps.

Results: During phonologic assembly, cerebellar activation was observed in the middle and posterior aspects of the posterior superior fissure and adjacent simple lobule and semilunar lobule bilaterally and in posterior aspects of the simple lobule, superior semilunar lobule, and inferior semilunar lobule bilaterally. Semantic processing, however, resulted in activation in the deep nuclear region on the right and in the inferior vermis, in addition to posterior areas active in phonologic assembly, including the simple, superior semilunar, and inferior semilunar lobules.

Conclusion: The cerebellum is engaged during reading and differentially activates in response to phonologic and semantic tasks. These results indicate that the cerebellum contributes to the cognitive processes integral to reading.

fig 1.

Composite maps (first order, see Table) show regional cerebellar activation during the four reading tasks. Column one compares the case task with the line task (C/L), column two compares the word rhyme task with the line task (WR/L), column three compares the non-word rhyme task with the line task (NWR/L), and column four compares the category task with the line task (CT/L). There is a progressive increase in demand on cognitive processing in going from column one to column four. Numbers indicate cerebellar regions that were more active (P = .005, red-yellow scale) in a reading task compared with the line task; letters indicate areas of the cerebellum that were more active (P = .005, blue-purple scale) in the line task compared with a reading task. 1, anterior aspect of the simple lobule; 2, middle and lateral aspects of the posterior superior fissure and adjacent simple lobule and superior semilunar lobule; 3, middle aspect of the horizontal fissure and adjacent superior semilunar lobule and inferior semilunar lobule; 4, middle aspect of the prepyramidal fissure and adjacent inferior semilunar lobule; 5, posterior and lateral aspects of the horizontal fissure and adjacent superior semilunar lobule and inferior semilunar lobule; 6, posterior and lateral aspects of the posterior superior fissure and adjacent simple lobule and superior semilunar lobule; 7, posterior aspect of inferior semilunar lobule; and 8, posterior and medial aspects of the posterior superior fissure and adjacent simple lobule and superior semilunar lobule. a, inferior vermis; b, postpyramidal fissure and medial aspect of the tonsils; c, biventer lobule; d, medial aspect of the biventer lobule; and e, the middle and posterior aspects of the horizontal fissure and adjacent superior semilunar lobule and inferior semilunar lobule. Section locations in each column from superior to inferior correspond to the following approximate y axis positions of the Talairach atlas: −40, −50, −60, −70, −80, and −90.

fig 2.

Composite maps (second order, see Table) contrast cerebellar activation during different reading conditions. The SPMs from the case/line comparison served as a baseline for comparison with the SPMs from other task comparisons to generate the three composite maps: non-word rhyme (non-word rhyme/line versus case/line, column one), word rhyme (word-rhyme/line versus case/line, column two), and category (category/line versus case/line, column three). Numbers indicate cerebellar regions that were more active (P = .005, red-yellow scale) in either category/line, word rhyme/line, or non-word rhyme/line compared with case/line, respectively. Column two (word rhyme) shows no significant difference in activation between word rhyme/line and case/line. In the non-word rhyme condition (column 1, arrow A) , participants performed the same task (judge whether letter strings rhyme) as in the word rhyme condition but on unfamiliar stimuli (non-word letter strings). Activation in the non-word rhyme condition occurred in the medial aspect of posterior superior fissure and adjacent simple lobule and superior semilunar lobule bilaterally (1), the medial and posterior aspects of the superior semilunar lobule bilaterally (3), the posterior aspect of the posterior superior fissure and adjacent simple and superior semilunar lobules bilaterally (4), the posterior and medial aspect of the simple lobule on the right (6), and the posterior and medial aspects of the inferior semilunar lobule on the left (7). In the category condition (column 3, arrow B), participants viewed similar stimuli (word pairs) as in the word-rhyme condition but were required to make a more elaborate semantic analysis (category judgment versus rhyme judgment). Cerebellar activation in the category condition was observed in the right deep nuclear region (2), the middle and posterior aspects of the horizontal fissure and adjacent superior semilunar lobule and inferior semilunar lobule bilaterally (3), the inferior vermis (5), the posterior and medial aspects of the simple lobule bilaterally (6), and the posterior and medial aspects of the inferior semilunar lobule bilaterally (7). There were no areas of the cerebellum that were more active (P = .005, blue-purple scale) in the case/line condition compared with the other reading conditions. Section locations in each column from superior to inferior correspond to the following y axis positions of the Talairach atlas: −40, −50, −60, −70, −80, and −90.