Several neural systems contribute to the control of visually guided rapid eye movements which include portions of the occipital, parietal, and frontal lobes and the superior colliculi. The cortical regions involved can be divided into two major systems, the anterior and the posterior. The anterior system is comprised of the frontal eye fields and the dorsomedial frontal cortex (DMFC) that gives rise to two major pathways coursing to subcortical regions; the posterior system is also comprised of two major pathways, one emanating from the occipital and the other from the parietal cortex. The posterior system reaches brain-stem eye-movement control centers through the superior colliculus; the anterior system has direct connections to the brain-stem. The major focus of the proposed work is to understand the manner in which these two major cortical systems control visually guided eye movements, with special emphasis on area DMFC about which at present relatively little is known. Especially poorly understood is the manner in which DMFC controls both eye and limb movements and the extent to which its neurons can be altered by experience.
The aim of the proposed work is to determine (1) how various regions of area DMFC control eye, head and limb movements, (2) how the organization of DMFC and the frontal eye fields is altered during the learning of new visuo-motor tasks, (3) how pharmacological inactivation or lesions of the DMFC and the frontal eye fields affects visuo-motor control and (4) how visually guided eye- movement control is affected when paired lesions are made that result in the isolation of structures that comprise the anterior or posterior systems. To answer these questions, trained, behaving rhesus monkeys will be studied using recording, stimulation and lesions methods. Some of the work will be done using newly developed chronic multiple single- cell recordings and microstimulation. The proposed research will increase our knowledge of the neural control of eye and limb movements which is essential for the understanding of malfunctions in human motor control due to brain damage. Particularly relevant is the fact that eye and limb control is often carried out in parallel by several systems which allows for significant recovery of function through systems left intact after brain damage.
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