Stefan F. Bucher

Functional MRI mapping of occipital and frontal cortical activity during voluntary and imagined saccades

We investigated the activation of frontal and occipital cortical areas in 14 normal volunteers during voluntary saccades in light or dark and during imagined saccades using functional magnetic resonance imaging (FMRI) with electro-oculogram monitoring. Voluntary saccades in light or dark and imagined saccades led to a significant activation (p < 0.005) of the precentral and posterior medial frontal gyrus (frontal eye field). The medial part of the superior frontal gyrus (supplementary eye field) also showed significant activity during voluntary saccades in all subjects, but only in four subjects during imagined saccades. In addition to frontal activity we found an activated primary visual cortex during voluntary saccades, both in light and in dark. In contrast to executed saccades, imagined eye movements revealed no occipital response under either condition. Our FMRI study supports the concept of frontal eye fields during voluntary saccades and demonstrates that occipital areas are associated with the generation of voluntary eye movements. However, the primary visual cortex is not active when eye movement is only imagined.

Cortical activation patterns during voluntary blinks and voluntary saccades

Objective: To investigate the activation of frontal, parietal, and occipital areas in normal volunteers during voluntary blinks and during voluntary saccades using functional MRI (fMRI). Background: A previous fMRI study revealed the activation of the precentral and posterior middle frontal gyrus (“frontal eye field” [FEF]), the medial part of the superior frontal gyrus (“supplementary eye field” [SEF]), and the visual cortex. The parietal cortex was not included in this study. Frontal and occipital cortical areas involved in voluntary blinking have not been shown previously using fMRI. Methods: A 1.5-T standard clinical scanner was used for both anatomic and functional studies in 12 observers. To conduct data analyses the authors used voxel-by-voxel cross-correlation. Results: Voluntary blinks led to the activation (p < 0.05) of the FEF, the SEF, the posterior parietal cortex (“parietal eye field” [PEF]), and the visual cortex. Voluntary blinking produced activity in the same cerebral structures as voluntary saccades. However, the number of activated voxels was smaller during voluntary blinking than during voluntary saccades in the visual cortex and in the FEF (p < 0.01). In contrast, the extent of activation was significantly higher (p < 0.003) in the SEF and in the PEF during voluntary blinking. Conclusions: Voluntary blinks and saccades are associated with similar loci of activation patterns; however, the quantitative distribution of activation suggests that the middle part of the frontal gyrus and posterior parietal cortex are of special significance for voluntary blinks. The results argue for the importance of considering quantitative distributional properties of parallel cortical activities associated with saccades and blinks.

Cerebellar activation during optokinetic stimulation and saccades

Objective: To investigate the activation pattern of cerebellar structures during small-field optokinetic stimulation (OKN) by functional MRI (fMRI) and compare it with that obtained during voluntary saccades and fixation suppression of OKN. Methods: Functional images were acquired from oblique transverse slices of eight healthy, right-handed volunteers using a radio frequency-spoiled, single-slice, fast low-angle shot (FLASH) pulse sequence with high-spatial resolution. Results: Horizontal OKN and saccades were associated with bilateral activity in the cerebellar hemispheres (superior semilunar lobule, simple lobule, quadrangular lobule, inferior semilunar lobule), the middle cerebellar peduncle, the dentate nucleus, and medially in the culmen and uvula of cerebellar nuclei. The pattern and extent of activation were independent of the stimulus direction for OKN and saccades. During fixation suppression, the extent of activation was significantly diminished (hemispheres) or even absent (uvula, culmen). Conclusion: The differential effects of fixation suppression on this complex pattern of cerebellar activation in part allow us to separate visual and attentional from ocular motor processing. Our data agree with behavioral and physiologic animal data about ocular motor processes and motor learning in the vestibulospinal and optokinetic reflex. This suggests that hemispheric cerebellar activity may be mainly associated with changes in attention, whereas vermal activity seems to be associated with ocular motor control, and activity of the dentate nuclei and the cerebellar peduncles seems to be associated with both.

Sensorimotor cerebral activation during optokinetic nystagmus A functional MRI study

Self-motion or object motion can elicit optokinetic nystagmus (OKN), which is an integral part of dynamic spatial orientation. We used functional MR imaging during horizontal OKN to study cerebral activation patterns in sensory and ocular motor areas in 10 subjects. We found activation bilaterally in the primary visual cortex, the motion-sensitive areas in the occipitotemporal cortex (the middle temporal and medial superior temporal areas), and in areas known to control several types of saccades such as the precentral and posterior median frontal gyrus, the posterior parietal cortex, and the medial part of the superior frontal gyrus (frontal, parietal, and supplementary eye fields). Additionally, we observed cortical activation in the anterior and posterior parts of the insula and in the prefrontal cortex. Bilateral activation of subcortical structures such as the putamen, globus pallidus, caudate nucleus, and the thalamus traced the efferent pathways of OKN down to the brainstem. Functional MRI during OKN revealed a complex cerebral network of sensorimotor cortical and subcortical activation.

High-resolution activation mapping of basal ganglia with functional magnetic resonance imaging

Article abstract-We investigated the activation of the putamen and the external and internal division of the globus pallidus in 12 normal volunteers during rapid supination and pronation of their right or left hand, using functional MRI (fMRI). We observed an increase in signal intensity varying from 3.1 +\- 1.2% to 23.4 +\- 2.3% during activation. Activated areas were predominantly contralateral to the moving hand and smaller than 5 mm2. These findings indicate that fMRI allows study of the normal function of basal ganglia and may be of value in the investigation of basal ganglia disorders. NEUROLOGY 1995;45: 180-182