The long-term goal of this laboratory is to understand the contributions made by the primate's cerebral cortex to the control of motor behavior. Experiments are focused on the role of the rhesus monkey's frontal and supplementary eye fields (FEF & SEF) in the generation of eye movements. These areas have been identified in both human and non-human primates and appear to be particularly important for eye movements that are driven by cognitive processes, for example, when a saccade is made to a remembered location or for the patterns of eye movements generated during reading The FEF and SEF have a number of features in common: they both contain neurons whose firing is related to the generation of saccades, and they both project to the superior colliculus and to oculomotor regions of the pons. There are also notable differences. Studies suggest that the FEF is more closely tied to sensory-motor processes, and is concerned with the generation of the next saccade. The SEF may be situated at a slightly higher level, and is involved in the planning of sequences of several saccades. This project is designed to expand our knowledge about the respective roles of the FEF and SEF in the control of saccades by identifying the types and effects of signals these two areas send to oculomotor regions in the brainstem, and by comparing the contributions of these two areas to the generation of natural scanning eye movements. The project has two components. The first examines the activity of identified SEF cells that project to the superior colliculus or to oculomotor regions of the pons. This will be done by antidromically exciting SEF neurons from the brainstem, and will identify signals sent by the SEF to pontine and collicular oculomotor centers. In addition, the effects of inputs from the FEF and SEF to superior colliculus and pons will be examined using orthodromic stimulation of cortex while recording from brainstem neurons, and by cross-correlation analysis of simultaneous recordings made from cortex and brainstem. The second component employs a new behavioral paradigm to evoke natural scanning eye movements. In this paradigm, eye movements and neural activity are recorded while a monkey freely views projected visual images. FEF and SEF eye activity during this paradigm will be compared to the activity occurring during conventional visuomotor tasks. The importance of these two areas for the generation of eye movements in this paradigm will be examined by artificially increasing or decreasing activity in a localized region by injection of the GABA antagonist bicuculline or agonist muscimol, or by inactivating a localized region with a microinjection of lidocaine. Together, these experiments will further our understanding of the role of these regions of frontal cortex in the control of eye movements, and will aid in the understanding of the differences between the FEF and SEF in their roles in the control of eye movements. The brains of rhesus monkeys and humans are similar, and the principles of function and organization revealed by these experiments are likely to apply to humans.
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| Ratcliff, Roger; Hasegawa, Yukako T; Hasegawa, Ryohei P et al. (2007) Dual diffusion model for single-cell recording data from the superior colliculus in a brightness-discrimination task. J Neurophysiol 97:1756-74 |
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| Hasegawa, Ryohei P; Hasegawa, Yukako T; Segraves, Mark A (2006) Single trial-based prediction of a go/no-go decision in monkey superior colliculus. Neural Netw 19:1223-32 |
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