Current perspectives on the cerebellum and reading development

Abstract

The dominant neural models of typical and atypical reading focus on the cerebral cortex. However, Nicolson et al. (2001) proposed a model, the cerebellar deficit hypothesis, in which the cerebellum plays an important role in reading. To evaluate the evidence in support of this model, we qualitatively review the current literature and employ meta-analytic tools examining patterns of functional connectivity between the cerebellum and the cerebral reading network. We find evidence for a phonological circuit with connectivity between the cerebellum and a dorsal fronto-parietal pathway, and a semantic circuit with cerebellar connectivity to a ventral fronto-temporal pathway. Furthermore, both cerebral pathways have functional connections with the mid-fusiform gyrus, a region implicated in orthographic processing. Consideration of these circuits within the context of the current literature suggests the cerebellum is positioned to influence both phonological and word-based decoding procedures for recognizing unfamiliar printed words. Overall, multiple lines of research provide support for the cerebellar deficit hypothesis, while also highlighting the need for further research to test mechanistic hypotheses.

Keywords: Cerebellar deficit hypothesis; Decoding; Network; Phonological; Reading development; Semantic.

Figure 1

Proposed cerebellar components that contribute to the development of reading according to a consensus paper. Image reprinted from “Consensus Paper: Language and the Cerebellum: An Ongoing Enigma” by P. Mariën et al., 2014, Cerebellum, 13, p. 399. Permission to be obtained.

Figure 2

Comparison of the three reading-related networks as determined by the ALE and Neurosynth map. (A) Activation comparison of the fractionated reading network regions for the six ALE phonological > semantic (green) and semantic > phonological (blue) clusters with the Neurosynth reverse inference map for the term reading (red). Spheres indicate each localized ALE cluster’s centroid voxel. Images were analyzed in MNI space and overlaid onto a 2×2×2 anatomical template provided by Brainmap.org (http://brainmap.org/). (B) Bar graph of the ALE phonological > semantic, semantic > phonological, and Neurosynth reading seed-voxels’ preferential bias towards functional terms. A 3 mm sphere was centered on each seed-voxel and placed onto the Neurosynth reverse inference maps for the terms phonological (green bars), semantic (blue bars), and reading (red bars). For each sphere, the average z-values were extracted and compared across the three reverse inference maps. Horizontal line indicates the significance threshold (z > 1.96). Regions in boldface font indicate functional connectivity with the cerebellum in subsequent analysis.

Figure 3

Functional connectivity results between the cerebral regions within the reading network and the cerebellum. (A) Functional connections between the inferior frontal junction from the Neurosynth reading map and the inferior parietal lobule from the ALE phonological > semantic map showed functional connectivity convergence with a cerebellar region localized in lobule HVIIb/Crus2 (cerebellar coordinate is the mean centroid voxel from the IFJ and IPL connectivity analyses). (B) Functional connectivity between the inferior frontal junction and the middle temporal gyrus from the ALE semantic > phonological map showed functional connectivity convergence to a medial section of the cerebellum localized around Crus1/Crus2 (cerebellar coordinate is the mean centroid voxel from the IFJ and MTG connectivity analyses). (C) The middle temporal gyrus also revealed a direct connection to a more posterior-lateral cerebellar region of lobule Crus1. The identified cerebellar regions were structurally normalized and localized using a hi-resolution Spatially Unbiased Atlas Template (SUIT; J. Diedrichsen et al., 2011; Jörn Diedrichsen, Balsters, Flavell, Cussans, & Ramnani, 2009). Time-series correlation for peak centroids was set at a voxel-wise threshold of r > .25, and cluster volume of 50 mm³.

Figure 4

Top 12 terms (highest z-value) corresponding to the seed-voxel for the functionally connect cerebro-cerebellar regions, as determined by Neurosynth’s term association metrics. Neuroanatomical and redundant terms were excluded and replaced with the next greatest associated term.

Figure 5

Cerebro-cerebellar dorsal circuit. Dashed line indicates a proposed indirect cerebellar support in developing orthographic knowledge stored in the mFG via direct modulatory connections with the fronto-parietal pathway for phonological processing.