Cerebellar contributions to sequence prediction in verbal working memory

Jutta Peterburs,Laura C Blevins,Yi-Shin Sheu,John E Desmond

doi:10.1007/s00429-018-1784-0

Abstract

Verbal working memory is one of the most studied non-motor functions with robust cerebellar involvement. While the superior cerebellum (lobule VI) has been associated with articulatory control, the inferior cerebellum (lobule VIIIa) has been linked to phonological storage. The present study was aimed to elucidate the differential roles of these regions by investigating whether the cerebellum might contribute to verbal working memory via predictions based on sequence learning/detection. 19 healthy adult subjects completed an fMRI-based Sternberg task which included repeating and novel letter sequences that were phonologically similar or dissimilar. It was hypothesized that learning a repeating sequence of study letters would reduce phonological storage demand and associated right inferior cerebellar activations and that this effect would be modulated by phonological similarity of the study letters. Specifically, while increased phonological storage demand due to high phonological similarity was expected to be reflected in increased right inferior cerebellar activations for similar relative to dissimilar study letters, the reduction in activation for repeating relative to novel sequences was expected to be more profound for phonologically similar than for dissimilar study letters, especially at higher memory load. Results confirmed the typical effects of cognitive load (5 vs. 2 study letters) and phonological similarity in several cerebellar and neocortical brain regions as well as in behavioral data (accuracy and response time). Importantly, activations in superior and inferior cerebellar regions were differentially modulated as a function of similarity and sequence novelty, indicating that particularly lobule VIIIa may contribute to verbal working memory by generating predictions of letter sequences that reduce the likelihood of phonological loop failure before stored items need to be retrieved. The present study is consistent with other investigations that support prediction, which can be based on sequence learning or detection, as an overarching cerebellar function.

Highlights

Recent research has highlighted a role of the cerebellum in motor behavior and in cognition
One of the most-studied non-motor functions with robust cerebellar involvement is working memory, and one of the experimental paradigms commonly used to study verbal working memory is a variant of the Sternberg Task (Sternberg 1966) in which subjects are presented with strings of study letters in the initial encoding phase, which they rehearse for several seconds while waiting for the presentation of a probe letter, which they have to match to the initially presented study letters
The present study was aimed to further elucidate how the cerebellum contributes to verbal working memory

Summary

Introduction

Recent research has highlighted a role of the cerebellum in motor behavior and in cognition. It has been proposed that, due to its uniform neuro-architecture with closed input–output loops that connect cerebellum and cerebrum (Middleton and Strick 1994; Strick et al 2009), the cerebellum possesses uniform processing habits to enable overarching, domain-independent functions such as monitoring, coordination, and timing (Strick et al 2009) Along these lines, the cerebellum may provide other basic functions such as sensory acquisition (Gao et al 1996; Bower 1997; Shih et al 2009), internal modelling/error correction (Wolpert et al 1998; Ito 2008), performance monitoring (Peterburs and Desmond 2016), and sequence detection (Braitenberg et al 1997; Molinari et al 2008; Leggio and Molinari 2015; Tedesco et al 2017). Subsequent neuropsychological studies have demonstrated that cerebellar damage produces abnormalities in phonological storage-related phenomena such as the phonological similarity effect (Justus et al 2005; Kirschen et al 2008), and studies with cerebellar patients have associated the inferior cerebellum with such abnormalities (Kirschen et al 2008; Chiricozzi et al 2008)

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Conclusion