Sensory acquisition functions of the cerebellum in verbal working memory

Abstract

Several fMRI studies have shown that the superior cerebellum exhibits load-dependent activations during encoding of letters in a Sternberg verbal working memory (VWM) task. It has been hypothesized that the cerebellum regulates the acquisition of sensory data across all modalities, and thus, that VWM load activations may reflect high- vs low-load differences in sensory acquisition demands. Therefore, increased difficulty in sensory data acquisition should elicit greater activation in the cerebellum. The present fMRI study manipulated sensory acquisition in VWM by presenting visually degraded and non-degraded stimuli with high and low memory loads, thereby identifying load-dependent regions of interest in the cerebellum, and then testing if these regions showed greater activation for degraded stimuli. Results yielded partial support for the sensory acquisition hypothesis in a load-dependent region of the vermis, which showed significantly greater activation for degraded relative to non-degraded stimuli. Because eye movements did not differ for these stimulus types, and degradation-related activations were present after co-varying eye movements, this activation appears to be related to perceptual rather than oculomotor demands. In contrast to the vermis, load-sensitive regions of the cerebellar hemispheres did not show increased activation for degraded stimuli. These findings point to an overall function of association-based prediction that may underlie general cerebellar function, with perceptual prediction of stimuli from partial representations occurring in the vermis, and articulatory prediction occurring in the hemispheres.

Keywords: Cerebellum; Cognition; Eye tracking; Sensory acquisition; Working memory.

Fig. 1

Schematic illustration of the sequence and time course of stimulus presentation in a trial of the Sternberg verbal working memory task

Fig. 2

Working memory behavioral results. Mean percentage of correct response a, mean RTs b and mean eye movement parameters c according to load and stimulus quality

Fig. 3

Positive cerebellar activations for high vs low cognitive load (high > low). p < 0.005 uncorrected. LHVI left hemispheral lobule VI, RHVI right hemispheral lobule VI

Fig. 4

Load effect (high > low; left panel) and stimulus quality effect (degraded > non-degraded; right panel) in Vermis Crus II (small volume corrected, p < 0.005)

Fig. 5

Stimulus quality effect (degraded > non-degraded; whole brain, FWE-corrected, p < 0.05) in left fusiform gyrus and right inferior occipital gyrus (upper panel), and load effect (high > low) in a small cluster in left fusiform gyrus (lower panel). Inf Occip Gyr inferior occipital gyrus, Fusiform gyr fusiform gyrus