Functional MRI of Double Step Saccades
The medial surface of the hemispheres including the cingulate cortex shows an important functional heterogeneity (Vogt et al. 1992). Experimental studies in animals and studies in humans provided evidence that the medial wall is involved in motor control, in attentional and emotional processes, and in eye movements. Furthermore, there is a fundamental dichotomy between functions of the anterior part of the cingulate cortex which serves primarily executive function and the posterior cingulate cortex controlling evaluative functions such as spatial orientation and memory (Vogt et al. 1992). For eye movement control, the role of the cingulate cortex is not fully understood. Most of the functional studies in humans described activity in the anterior (Paus et al. 1993; O’Sullivan et al. 1995; Sweeney et al. 1996; Doricchi et al. 1997) or median cingulum (Petit et al. 1993; 1996; Lang et al. 1994) during eye movements or fixation (Anderson et al. 1994; Petit et al. 1995). However, the observed activity in different studies was not always consistent, and activity seems to be dependent on the ocular motor paradigm. On the other hand, single cell recordings in animals suggest that the posterior cingulate region plays an important role in eye movement control: Olson et al. (1996) found neurons in the posterior cingulate that fired during periods of ocular fixation, dependent on eye position in the orbita and of the size and direction of the preceding eye movement. Furthermore, discharging rate changed during saccadic eye movements, and many neurons exhibited significant excitation after saccades. Similar results were found in the posterior cingulate cortex of the cat (Olson and Musil 1992).
KeywordsSupplementary Motor Area Primary Visual Cortex Medial Wall Posterior Cingulate Cortex Positron Emission Tomogra
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