Functional activation in the cerebellum during working memory and simple speech tasks

Abstract

Verbal working memory is the ability to temporarily store and manipulate verbal information. This study tested the predictions of a neuroanatomical model of how the cerebellum contributes to verbal working memory (Desmond et al., 1997). In this model, a large bilateral region in the superior cerebellum is associated with articulatory rehearsal and a right-lateralized region in the inferior cerebellum is associated with the correction of errors within the working memory system. The Desmond et al. (1997) model was based on neuroimaging findings using item recognition tasks and comparisons between working memory and covert rehearsal tasks, whereas in this functional magnetic resonance imaging (fMRI) study we used a delayed serial recall (DSR) task because it relies more heavily on articulatory rehearsal, and our comparison tasks included both overt and covert speech tasks. Our results provide some support for the Desmond et al. (1997) model. In particular, we found multiple activation foci within the superior and inferior sectors of the cerebellum and evidence that these regions show different patterns of activation across working memory and speech tasks. However, the specific patterns of activation were not fully consistent with those reported by Desmond et al. (1997). Namely, our results indicate that activation in the superior sector should be functionally subdivided into a medial focus involved in speech processing and a lateral focus more specific to verbal working memory; the results also indicate that activation in the inferior sector is not uniquely right lateralized. These complex findings speak to the need for future studies to consider the speech-motor aspects of tasks, to investigate the functional significance of adjacent peaks of activation within large regions of cerebellar activation, and to use analysis procedures that support regional distinctions through direct statistical tests. Such studies would help to refine our understanding of how the cerebellum contributes to speech and verbal working memory.

Fig 1

Functional activations during the verbal working memory and simple speech tasks across the superior and inferior sectors of the cerebellum (superior split into: superio-medial, superio-lateral). (a) Overlap of the seven regions identified from the encoding and the retrieval epochs of the DSR task. (b) Overlap of the regions identified from the DSR task and simple covert and overt speech tasks. (c) Average percent signal change across the DSR and speech tasks in six of the bilateral regions identified from the encoding and retrieval contrasts. Note that data is shown for only one of the two left inferior regions listed in Table 1. The excluded left inferior cerebellar region showed a similar pattern of activation.

Fig 2

Graphical representation of the two-way interactions from the ANOVAs. (a) Interaction between condition and sector showing the significant difference between overt and covert speech in the superio-medial sector. (b) Interaction between task and hemisphere showing that the DSR task had significantly higher percent signal change in the right hemisphere than the simple speech task.

Fig 3

Overlap of the regions identified from the DSR task and simple overt tapping tasks.