The generation of rapid or saccadic eye movements requires a transformation from the visual input falling on the retina to the pulse of activity to the eye muscles to move the eyeball to a new position. The areas in the brain of primates (an excellent animal model of the human saccadic system) have been identified throughout regions of the cerebral cortex and brainstem so that in outline the entire pathway from visual input to eye movement output is now known. What is not know is what signals are conveyed from one region to the next and what transformations in that signal are made at each stage of processing in the brain, and until this is known, a circuit within the brain for the control of behavior can not be understood. We have addressed this issue by determining which neurons in two cortical areas, the frontal eye fields, and the posterior parietal cortex, are the output neurons to the brainstem center for the control of saccades, the superior colliculus. By electrically stimulating in the colliculus, we can activate the axons of neurons in cortex that reach to the colliculus (antidromic activation) and thereby see which neurons are the output neurons from cortex and what is the nature of the signal (visual, visuomotor, motor) that they carry. About three quarters of the antidromically activated neurons in the parietal cortex respond to the visual stimulation that could be used to guide a saccade. In addition, these neurons were active as the monkey prepared to make a saccade to a visual target indicating that the neurons going from this region of cortex to the brainstem were carrying both a visual and a movement related signal. This signal is similar to that carried by one set of neurons in the colliculus thought to be at the earliest stage of processing in that structure, the buildup neurons. In contrast, when the same experiment was done with neurons in the frontal eye field, more neurons tended to have a clear burst of neuronal activity before the onset of the saccade. These neurons were more like the neurons in the colliculus that are close to the output of that structure, the burst neurons. Thus the major output of the two areas of the cerebral cortex is different and may represent the input to different stages of signal processing in the superior colliculus, a possibility that we are now investigating. In addition to the signal going to the colliculus from cortex, we have also identified one from colliculus to the frontal eye fields (orthodromic activation), and found that all of the neurons in the frontal eye fields that receive this signal have visual activity. Thus the neurons that project out of the frontal eye fields to colliculus tend to carry a motor signal while those that receive information from the colliculus have a visual signal.
| Berman, Rebecca A; Joiner, Wilsaan M; Cavanaugh, James et al. (2009) Modulation of presaccadic activity in the frontal eye field by the superior colliculus. J Neurophysiol 101:2934-42 |
| Sommer, Marc A; Wurtz, Robert H (2008) Brain circuits for the internal monitoring of movements. Annu Rev Neurosci 31:317-38 |
| Sommer, Marc A; Wurtz, Robert H (2008) Visual perception and corollary discharge. Perception 37:408-18 |
| Wurtz, Robert H (2008) Neuronal mechanisms of visual stability. Vision Res 48:2070-89 |
| McAlonan, Kerry; Cavanaugh, James; Wurtz, Robert H (2008) Guarding the gateway to cortex with attention in visual thalamus. Nature 456:391-4 |
| Sommer, Marc A; Wurtz, Robert H (2006) Influence of the thalamus on spatial visual processing in frontal cortex. Nature 444:374-7 |
| Nakahara, Hiroyuki; Morita, Kenji; Wurtz, Robert H et al. (2006) Saccade-related spread of activity across superior colliculus may arise from asymmetry of internal connections. J Neurophysiol 96:765-74 |
| Cavanaugh, James; Alvarez, Bryan D; Wurtz, Robert H (2006) Enhanced performance with brain stimulation: attentional shift or visual cue? J Neurosci 26:11347-58 |
| McAlonan, Kerry; Cavanaugh, James; Wurtz, Robert H (2006) Attentional modulation of thalamic reticular neurons. J Neurosci 26:4444-50 |
| Hanes, Doug P; Smith, Mitchell K; Optican, Lance M et al. (2005) Recovery of saccadic dysmetria following localized lesions in monkey superior colliculus. Exp Brain Res 160:312-25 |
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