Functional topography of the cerebellum in verbal working memory

Abstract

Speech-both overt and covert-facilitates working memory by creating and refreshing motor memory traces, allowing new information to be received and processed. Neuroimaging studies suggest a functional topography within the sub-regions of the cerebellum that subserve verbal working memory. Medial regions of the anterior cerebellum support overt speech, consistent with other forms of motor execution such as finger tapping, whereas lateral portions of the superior cerebellum support speech planning and preparation (e.g., covert speech). The inferior cerebellum is active when information is maintained across a delay, but activation appears to be independent of speech, lateralized by modality of stimulus presentation, and possibly related to phonological storage processes. Motor (dorsal) and cognitive (ventral) channels of cerebellar output nuclei can be distinguished in working memory. Clinical investigations suggest that hyper-activity of cerebellum and disrupted control of inner speech may contribute to certain psychiatric symptoms.

Fig. 1

Anatomical and functional mapping of the cerebellum in verbal working memory, depicted on T2-weighted coronal sections (y=−50) (Schmahmann et al. 1999). a) The anterior, superior, and inferior cerebellar lobes are comprised of smaller lobes, as indicated by the matching colored labels. For simplicity, only the right hemisphere is described in the figure. D = dorsal, V = ventral, R = right, L = left. b) Lobular and deep nuclear cerebellar regions of interest that have been implicated in both functional neuroimaging and patient studies with different aspects of speech and working memory are mapped onto cerebellar anatomy. Anterior and superior lobe activations for overt speech and verbal working memory are often bilateral, but right-side dominant. Note that, on the right, Crus II and Lobe IX (stippled green lines) are not included in the functional description of the inferior lobe

Fig. 2

Peak activations within the right cerebellar dentate are shown for encoding and retrieval phases of the Sternberg task (Working Memory greater than Match conditions), p<.001. The green line at z=−37 is used to indicate a functional division between the dorsal and ventral dentate, which falls roughly between z=−36 to −40 (Dimitrova et al. 2006). This functional division is consistent with neuroanatomical tracing studies indicating that the dorsal dentate projects to motor regions of the frontal lobe, while the ventral dentate projects to cognitive frontal regions, implicating a “motor” dorsal dentate and a “cognitive” ventral dentate as illustrated in Fig. 1. R = right; L = left. From Marvel and Desmond (2010) with permission

Fig. 3

Correlation between fMRI signal in the right cerebellar Lobule VI and accuracy performance while subjects silently manipulated letters during a Sternberg working memory paradigm. Data represent 16 young, healthy adults, r=−.65, p<.01. The inverse relationship between these two variables suggests that superior cerebellar activity increased as subjects encountered difficulty with the task