Functional mapping of the human cerebellum with positron emission tomography.

Abstract

Alterations of local neuronal activity induced within the human cerebellum by tactile stimulation and voluntary movement were mapped with positron emission tomographic measurements of brain blood flow. Finger movements produced bilateral, parasagittal blood-flow increases in anterior, superior hemispheric cortex of the cerebellum. Responses to tactile finger stimulation were coextensive with responses to voluntary finger movements but were less intense. Saccadic eye movements produced midline blood-flow increases in the posterior vermis of the cerebellum. Positron emission tomography now permits investigation of functional-anatomical relations within the human cerebellum.Experimental investigation of the functional topography of the human brain began in 1874, when focal sensory responses to electrical stimulation of the exposed cortex of an awake subject were described (1). Since that time, numerous techniques have been developed for functional mapping of the human brain in vivo, including recording and stimulation of exposed cortical surfaces during neurosurgical intervention (particularly for focal epilepsy) (2), scalp-recorded evoked potentials (3), evoked magnetic-field recordings (4), transcalvarial electrical stimulation (5), and radiotracer measurements of blood flow and metabolism during the performance of activation paradigms (6). These methods, however, have been applicable only to the cerebral hemispheres, the largest and most accessible brain structures. The cerebellum, lying beneath the cerebrum in the posterior fossa of the skull, has remained inaccessible to activation recordings with techniques suitable for use in humans, primarily because of the anatomical characteristics of the cerebellum and its compartment. As the cerebellum is believed to be largely involved in the planning and execution of voluntary movements, recordings in awake, behaving subjects are of particular interest.Regional increases in neuronal activity during task performance and sensory stimulation induce like changes in regional blood flow and metabolism (7). Regional measurements of blood flow and metabolism can be obtained in vivo within the human brain by use of positron emission tomography (PET) (6). PET METHODSPET Techniques. The PETT VI system was employed for all emission and transmission tomographic measurements (11). Each emission scan was a seven-slice, quantitative measurement of regional tissue radioactivity. Each transmission scan was a reconstructed image of the regional attenuation of 511-keV photons from a 'Ge/'Ga ring source.Slices were 14.4 mm apart from center to center. In the low-resolution mode, this system has an in-plane reconstructed resolution of 12.4 mm full-width at half-maximum (FWHM) and a between-plane resolution of 13.9 mm FWHM in the center of the field of view. All scans were made in the low-resolution mode.Fifteen paid normal volunteers were studied. Permission for this study was obtained from the subjects in accordance with guidelines approved for this study by the Human Studies C...

Lateral cerebellar hemispheres actively support sensory acquisition and discrimination rather than motor control.

“…Thus, dentate nuclei are activated by purely sensory stimuli, confirming positron-emission tomography results showing cerebellar activation during hand vibration (Fox et al 1985). This activation was equally strong in the left and fight dentate but tended to be more extensive in the right dentate, probably reflecting the left cerebral dominance of our fight-handed subjects.…”

“…Classic theory has emphasized that the output of the deep cerebellar nuclei in mammals is to primarily influence motor structures (Asanuma et al 1983;Aumann et al 1994;Keifer and Houk 1994). Cerebellar activity during movement has been well confirmed by electrophysiological recordings in animals (Ojakangas andEbner 1992, 1994;Keifer and Houk 1994;van Kan et al 1994;Apps et al 1995) and by functional neuroimaging in humans (Fox et al 1985;Ellerman et al 1994). As a consequence, nearly all cellular and network level theories of cerebellar function focus on movement control (Marr 1969;Llin~is 1984;Bloedel and Kelly 1992;Kawato and Gomi 1992;Paulin 1993;Houk and Wise 1995;Martin and Albers 1995).…”

“…In addition, it is activated by tactile stimulation alone (without overt movement) (Fox et al 1985). Finally, determining whether a brain area has a motor or sensory function is a subtle, and often overlooked, problem.…”

Human cortical processing of colour and pattern

“…PET studies that have demonstrated activation of the cerebellum include those examining motor learning [Seitz et al, 1990], motor control [Fox et al, 1985], and tactile learning [Roland et al, 1987], as well as somatosensory discrimination [O'Sullivan et al, 1994]. It has been postulated that the cerebellum is involved in higher cognitive processing mediated through its reciprocal connections with the prefrontal cortex [Middleton and Strick, 1994].…”

Features of Eye Movement Disorders in Patients With Cerebellar Lesions of Different Localization

“…Именно методы нейровизуализации, а конкретно метод ПЭТ впервые выявил активацию определенных областей моз-жечка при совершении движений глаз [13]. Метод фМРТ позволяет как регист-рировать активацию мозжечка при вы-полнении разных типов движений глаз, так и производить сравнение показателей в норме и патологии при выполнении за-данной глазодвигательной задачи [14].…”