Visuomotor cerebellum in human and nonhuman primates.

In this paper, we will review the anatomical components of the visuomotor cerebellum in human and, where possible, in non-human primates and discuss their function in relation to those of extracerebellar visuomotor regions with which they are connected. The floccular lobe, the dorsal paraflocculus, the oculomotor vermis, the uvula-nodulus, and the ansiform lobule are more or less independent components of the visuomotor cerebellum that are involved in different corticocerebellar and/or brain stem olivocerebellar loops. The floccular lobe and the oculomotor vermis share different mossy fiber inputs from the brain stem; the dorsal paraflocculus and the ansiform lobule receive corticopontine mossy fibers from postrolandic visual areas and the frontal eye fields, respectively. Of the visuomotor functions of the cerebellum, the vestibulo-ocular reflex is controlled by the floccular lobe; saccadic eye movements are controlled by the oculomotor vermis and ansiform lobule, while control of smooth pursuit involves all these cerebellar visuomotor regions. Functional imaging studies in humans further emphasize cerebellar involvement in visual reflexive eye movements and are discussed.

fMRI activities in the emotional cerebellum: a preference for negative stimuli and goal-directed behavior.

Several studies indicate that the cerebellum might play a role in experiencing and/or controlling emphatic emotions, but it remains to be determined whether there is a distinction between positive and negative emotions, and, if so, which specific parts of the cerebellum are involved in these types of emotions. Here, we visualized activations of the cerebellum and extracerebellar regions using high-field fMRI, while we asked participants to observe and imitate images with pictures of human faces expressing different emotional states or with moving geometric shapes as control. The state of the emotions could be positive (happiness and surprise), negative (anger and disgust), or neutral. The positive emotional faces only evoked mild activations of crus 2 in the cerebellum, whereas the negative emotional faces evoked prominent activations in lobules VI and VIIa in its hemispheres and lobules VIII and IX in the vermis. The cerebellar activations associated with negative emotions occurred concomitantly with activations of mirror neuron domains such as the insula and amygdala. These data suggest that the potential role of the cerebellum in control of emotions may be particularly relevant for goal-directed behavior that is required for observing and reacting to another person's (negative) expressions.

Differences between smooth pursuit and optokinetic eye movements using limited lifetime dot stimulation: a functional magnetic resonance imaging study.

In this study, we examined possible differences in brain activation between smooth pursuit and optokinetic reflexive (OKR) eye movements using functional magnetic resonance imaging (fMRI). Eighteen healthy subjects performed two different eye movement paradigms. In the first paradigm, smooth pursuit eye movements were evoked by a single moving dot. In the second paradigm, optokinetic eye movements without a foveal smooth pursuit component were evoked by a moving pattern of multiple dots with a limited lifetime. As expected, the two eye movement systems show overlapping pathways, but the direct comparison of the activation patterns between the two experiments showed that the frontal eye field, MT/V5 and cerebellar area VI appear to be more activated during smooth pursuit than during optokinetic eye movements. These results showed that the smooth pursuit and optokinetic eye movement systems can be differentiated with fMRI using limited lifetime dots as an effective OKR stimulus.

Cortical and cerebellar activation induced by reflexive and voluntary saccades.

Reflexive saccades are driven by visual stimulation whereas voluntary saccades require volitional control. Behavioral and lesional studies suggest that there are two separate mechanisms involved in the generation of these two types of saccades. This study investigated differences in cerebral and cerebellar activation between reflexive and self-paced voluntary saccadic eye movements using functional magnetic resonance imaging. In two experiments (whole brain and cerebellum) using the same paradigm, differences in brain activations induced by reflexive and self-paced voluntary saccades were assessed. Direct comparison of the activation patterns showed that the frontal eye fields, parietal eye field, the motion-sensitive area (MT/V5), the precuneus (V6), and the angular and the cingulate gyri were more activated in reflexive saccades than in voluntary saccades. No significant difference in activation was found in the cerebellum. Our results suggest that the alleged separate mechanisms for saccadic control of reflexive and self-paced voluntary are mainly observed in cerebral rather than cerebellar areas.

fMRI of optokinetic eye movements with and without a contribution of smooth pursuit.

BACKGROUND AND PURPOSE: Optokinetic eye movements are elicited when tracking a moving pattern. It can be argued that a moving pattern of stripes invokes both the optokinetic and the smooth pursuit eye movement system, which may confound the observed brain activation patterns using functional magnetic resonance imaging (fMRI). A moving pattern of limited-lifetime-dot stimulation does not target the smooth pursuit eye movement system. METHODS: fMRI was used to compare the cortical activity elicited by an optokinetic eye movement response evoked by a moving pattern of stripes and a moving pattern of limited lifetime dots. RESULTS: The eye movement behavior showed that both types of stimuli evoked an adequate and similar optokinetic eye movement response, but stimulation with stripes evoked more activation in the frontal and parietal eye fields, MT/V5, and in the cerebellar area VI than stimulation with limited-lifetime dots. CONCLUSIONS: These brain areas are implicated in smooth pursuit eye movements. Our results suggest that indeed both the optokinetic and the smooth pursuit eye movement system are involved in tracking a moving pattern of stripes.

An fMRI study on smooth pursuit and fixation suppression of the optokinetic reflex using similar visual stimulation.

This study compares brain activation patterns evoked by smooth pursuit and by fixation suppression of the optokinetic reflex (OKR) using similar retinal stimulation. Functional magnetic resonance imaging (fMRI) was performed during smooth pursuit stimulation in which a moving target was presented on a stationary pattern of stripes, and during fixation suppression of OKR in which a stationary target was presented on a moving pattern of stripes. All subjects could effectively ignore the background pattern and were able to keep the target continuously on the fovea with few saccades, in both experiments. Smooth pursuit evoked activation in the frontal eye fields (FEF), the supplementary eye fields (SEF), the parietal eye fields (PEF), the motion-sensitive area (MT/V5), and in lobules and vermis VI of the cerebellum (oculomotor areas). Fixation suppression of OKR induced activation in the FEF, PEF, and MT/V5. The direct comparison analysis revealed more activation in the right lobule VI of the cerebellum and in the right lingual and calcarine gyri during smooth pursuit than during fixation suppression of OKR. Using similar retinal stimulation, our results show that smooth pursuit and fixation suppression of the OKR appear to activate largely overlapping pathways. The increased activity in the oculomotor areas of the cerebellum during smooth pursuit is probably due to the presence of an active eye movement component.