Ocular motor system: anatomy and functional magnetic resonance imaging

This article reviews current positron emission tomography and functional MR imaging (fMRI) studies of brain activation and indicates some of the insights they provide into the neuronal network mediating motion-perception and ocular motor control. The complexity of the network and the activation of the entire system seemingly independent of the specific ocular motor task performed makes functional interpretation extremely difficult. At the same time, however, the complexity illustrates the dilemma of associating a particular locus with one specific function. Caution is required to differentiate specific from nonspecific effects, to identify activations and deactivations, and to distinguish which of the systems has been activated inadvertently through poor stimulus control. The next step required for meaningful correlations of structure with function is for fMRI studies to test neurologic patients with distinct and separate lesions of the network. Such a comparison must evaluate the effect of the ocular motor deficit on the lesion site and the connected network in the acute stage and then following functional recovery caused by plasticity and neuronal repair.