Natural behaviors are elicited by means of complex interactions between sensory and motor systems. Yet, the presumption of most experiments is that a peripheral stimulus is perceived by the sensory system, the cortex selects a response, and the motor system effects the behavior. This model of neural function is useful for studying sensory systems or motor mechanism. However, it is clear that this is not the only method by which the sensory information can influence behavior. Orienting movements allow animals to direct their attention toward stimuli of interest. These behaviors are essential in seeking food and shelter. Therefore, an animal's ability to orient is critical to it survival. The saccadic system has been studied extensively as a model of orienting behaviors. Moreover, it is well established that deficits in saccadic eye movements are found in a variety of neural dysfunctions. In this project, we propose to study how somatosensory information directly affects how the primate's zona incerta modulates saccadic eye movements. The zona incerta has large inputs from the contralateral principal sensory trigeminal and dorsal column nuclei. Therefore, it receives direct sensory information. Within the zona incerta, there are saccade- related neurons. These cells have moderate rates of activity that stop for eye movements. The zona incerta projects to the deepest layers of the superior colliculus where the final efferent signal for saccade is initiated. This pathway is thought to be GABAergic. Therefore, we have hypothesized that the zona incerta releases (stops inhibition of) collicular neurons that initiate saccadic eye movements. However, whether the sensory inputs into the zona incerta affect saccade is an open questions. In an effort to elucidate the functional role of the zona incerta, we will address four issues with this project using the primate saccadic system as a model. First, it is well established in many species that somatosensory information can reach the zona incerta by means of the projections form the trigeminal and dorsal column nuclei. This has not yet been demonstrate in the macaque. Therefore, in Specific Aim 1, we will study the extent of the somatosensory projection to the primate's zona incerta. Second, it is not established whether the inhibitor neurotransmitter GABA is used in the macaque's incertotectal projection as in other species. Therefore, in Specific Aim 2, we will first study whether the monkey's zona incerta contains GABA and/or glutamate and then examine which of these transmitters is contained in incertotectal neurons. Third, whether incerta neurons in the primate respond to somatosensory stimuli is ont known.
In Specific Aim 3, we will examine how somatosensory stimulation affects the activity of incerta neurons in the alert primate. Fourth, just because an incerta neurons has activity related to somatosensory stimulation does not mean that is also related to saccadic eye movements. Thus, in Specific Aim 4, we will examine whether the same cell fires for somatosensory stimuli and for saccade. Additionally, we will test how somatosensory cues might be used in directing saccade. In sum, this project will test the hypothesis that the zona incerta utilizes somatosensory information to affect orienting behaviors generated by the superior colliculus in the primate.
| Ma, T P; Lynch, J C; Donahoe, D K et al. (1998) Organization of the medial pulvinar nucleus in the macaque. Anat Rec 250:220-37 |
| Ma, T P; Johnson, J C; Hoskins, G A (1997) Organization of the zona incerta in the macaque: an electron microscopic study. Anat Rec 249:259-75 |
| Ma, T P (1996) Saccade-related omnivectoral pause neurons in the primate zona incerta. Neuroreport 7:2713-6 |
| Ma, T P; Hazlett, J C (1995) Cytoarchitecture of the substantia nigra pars lateralis in the opossum (Didelphis virginiana): a correlated light and electron microscopic study. Anat Rec 241:563-78 |
