The role of cerebral cortex in the generation of voluntary saccades: a positron emission tomographic study

Abstract

The purpose of this study was to define the location and behavior of cerebral structures within the normal human brain that participate in the generation of voluntary saccadic eye movements. Changes in regional cerebral blood flow (rCBF) during task performance were assumed to reflect like changes in regional neuronal activity induced by the task. The locations of all rCBF changes were described in stereotaxic coordinates. Cerebral blood flow (CBF) was measured with positron emission tomography (PET) and bolus intravenous injection of H2(15)O. The use of H2(15)O with PET allowed six, seven-slice measurements of brain blood flow to be made in rapid sequence for each subject, without removing the subject from the tomograph between scans. Nine paid normal volunteers were studied. The paradigm included three saccadic eye-movement (SEM) conditions, one finger-movement condition and two control conditions (initial and final). The three SEM conditions allowed comparisons to be drawn between targeted versus untargeted SEMs, auditorily cued versus visually cued SEMs, and stochastic versus rhythmic SEMs. All tasks were simple and deterministic in that each movement exactly mirrored the preceding movement: finger flexion then extension, saccade-left then saccade-right. Saccadic eye movements were associated with rCBF increases within the frontal eye fields, the supplementary motor area, and the cerebellum. Finger movements were associated with rCBF changes within the sensorimotor hand areas, the supplementary motor area, and the cerebellum. The frontal eye fields were discrete cortical regions consistently active during the generation of voluntary SEMs and uninfluenced by target presence, type of cue, or task complexity, indicating a predominantly motor function. The supplementary motor area (SMA) was consistently active during all motor tasks and was uninfluenced by the degree of task complexity or stochasticity. A role for SMA in establishing "motor set" during both simple and complex motor tasks is suggested. An anterior-posterior somatotopy was found for SMA-eye (anterior) versus SMA-hand (posterior). Lateral occipital visual association cortex activation was present only during targeted saccadic conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Cortical and cerebellar activation induced by reflexive and voluntary saccades

“…We did not observe any signiWcant activation in the SEF during saccadic eye movements. Activation in the SEF related to reXexive or voluntary saccade eye movements has been reported by some (Fox et al 1985;Darby et al 1996;Petit et al 1996;Law et al 1998;Luna et al 1998;Muri et al 1998;Berman et al 1999;Nobre et al 2000), but not by others (Anderson et al 1994;Mort et al 2003).…”

“…In our study, we also found that reXexive saccades yielded activation in the FEF, PEF, MT/V5 and in the angular gyrus, as well as in the cerebellum, more speciWcally in the cerebellar lobule VI, crus I and in the vermis VI and VII. For voluntary saccades, PET studies have shown activation in FEF (Fox et al 1985;Petit et al 1996;Law et al 1998), SEF (Fox et al 1985;Petit et al 1996;Law et al 1998), PEF (Petit et al 1996), PVA/V1 (Fox et al 1985), the anterior cingulate cortex (Paus et al 1993), the precuneus (Petit et al 1996), the midbrain and the cerebellar vermis (Petit et al 1996;Law et al 1998). fMRI studies have also shown activation in FEF (Darby et al 1996;Corbetta et al 1998), SEF (Darby et al 1996), PEF, PVA/V1, and the posterior vermis of the cerebellum (Corbetta et al 1998), as well as in V4.…”

Default brain functionality in blind people

“…Thus, changes in absolute blood flow in areas typically affected by cognitive tasks are rarely Ͼ5-10% of the brain's resting blood flow. These modest modulations in ongoing circulatory activity often do not appreciably affect overall brain blood flows during even vigorous sensory and motor activity (45)(46)(47). For interesting exceptions related to more demanding cognitive tasks see refs.…”

Comparison of neuronal activity in the supplementary motor area and primary motor cortex

“…It is now well known that the SMA, in addition to the MI, are active in such types of movements that does not require temporal or spatial control in any complex manner. Changes in rCBF have been reported during simple limb movements [9,17,18,21]. Movement related potentials have also been recorded in the SMA before flexion or extension of hand or arm joints [5,27,30,74].…”