Gaze shift is an important visuomoter process involving coordinated movements of the eyes and head for learning about the visual environment. A gaze shift involves not only moving the line of sight to foveate visual targets, but also aligning the head position with the gaze to permit2 flexible oculomotor movements with high visual acuity. This process is thought to involve the neural networks of the frontal cortex and those of the brainstem in order to orchestrate coherent movements. Recently, studies in the brainstem have shown that many of the previously assumed """"""""pure oculomoter"""""""" structures in fact control movements of both the eyes and the head. These findings pose serious challenges to our current understanding of oculomoter control in the frontal cortex as to whether t he cortex encodes eye movements alone, as the name """"""""oculomoter"""""""" claims, or gaze (i.e., coordinated movements of the eyes and head), as in the superior colliculus and other brainstem sites. Verifying these hypothesis will significantly advance our understanding of movement control. Because these issues have not been thoroughly investigated in part due to a lack of satisfying methodology to differentiate the contribution of eye and head during gaze shifts; we will attempt in the proposed experiments to use techniques that separate the contribution of the eyes and head to gaze. The results of electrical microstimulation, reversible inactivation/activation, and chronic single-unit recording will be related to predefined variables, such that the contribution of each movement can be sufficiently elaborated.
Under Specific Aim 1, we will study the function of the frontal eye field (FEF) and the supplementary eye field (SEF) on the control of movements of the eyes and head. Based on suggestions of previous studies and our preliminary findings, the FEF and the4 SEF are the most relevant oculomoter areas in the frontal cortex. We ask: both the FEF and the SEF neurons generate signals that control the movements of both the eyes and head, or does each region generate separate signals that control part of the movements? We will train head-unrestrained monkeys in tasks that separate the contribution of the eyes and head to gaze to assess these possibilities.
Under Specific Aim 2, we will study the mechanism of maintaining gaze/head alignment following changes in gaze. We hypothesize that a newly discovered region near the SEF participates in the control of this process by evoking head (not eye) movement to center the eyes in the orbit, irrespective of initial gaze positions in space. We will assess this hypothesis in the proposed experiments using the techniques mentioned above. The proposed studies will not only provide new information about how the frontal cortex controls gaze shifts, but also reveal important insights relating to now the neural networks of the cortex and brainstem together control gaze shifts.
| Chen, L Longtang (2006) Head movements evoked by electrical stimulation in the frontal eye field of the monkey: evidence for independent eye and head control. J Neurophysiol 95:3528-42 |
| Chen, L Longtang; Walton, Mark M G (2005) Head movement evoked by electrical stimulation in the supplementary eye field of the rhesus monkey. J Neurophysiol 94:4502-19 |
| Goffart, Laurent; Chen, Longtang L; Sparks, David L (2004) Deficits in saccades and fixation during muscimol inactivation of the caudal fastigial nucleus in the rhesus monkey. J Neurophysiol 92:3351-67 |
| Goffart, Laurent; Chen, Longtang L; Sparks, David L (2003) Saccade dysmetria during functional perturbation of the caudal fastigial nucleus in the monkey. Ann N Y Acad Sci 1004:220-8 |
