Saccade Abnomalities in Patients with Caudate Lesion
A saccade is a rapid eye movement that is generated by a burst of firing of neurons in the intermediate layer of the superior colliculus. Anatomical description of the projections from the substantia nigra pars reticulata, the output nucleus of the basal ganglia, to the intermediate layer of the superior colliculus shed light on the basal ganglia as an upper center in the saccade system (Jayaraman et al., 1977; Graybiel et al., 1978). Among the basal ganglia, neurons which show activities related to voluntary saccades in behaving monkeys have been found in the substantia nigra pars reticulata (Hikosaka and Wurtz, 1983), in the caudate nucleus (Hikosaka et al., 1989), in the subthalamic nucleus (Matsumura et al., 1992), and in the external pallidum (Kato and Hikosaka, 1992). In the substantia nigra pars reticulata, neurons were found that show a transient decrease of tonic high frequency firing before voluntary saccades. As the nigro-collicular projection was proved to be GABAergic, a transient decrease in firing of nigral neurons might produce a burst of a firing of collicular neurons (Hikosaka and Wurtz, 1985). In the caudate nucleus, neurons were found which show an increase in firing before saccades. The caudate-nigral projection is also thought to be GABAergic. Thus, it is proposed that saccades were initiated by the disinhibitory mechanism through the caudate-nigro-collicular pathway (Hikosaka et al., 1989). The subthalamic nucleus was proposed to enhance tonic firing of neurons of the substantia nigra pars reticulata and thus suppress unwanted eye movements (Matsumura et al., 1992). The external pallidum might be a modulator of this system (Hikosaka et al., 1993).
KeywordsBasal Ganglion Caudate Nucleus Target Point Subthalamic Nucleus Saccade Task
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