BEHAVIORAL CONTROL BY THE ZONA INCERTA

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.