Salk Institute for Biological Studies
Government Grants Promoting Cruelty to Animals
Salk Institute for Biological Studies, La Jolla, CA
RICHARD J. KRAUZLIS - Primate Testing - 2006
Grant Number: 2R01EY012212-09
Abstract: DESCRIPTION (provided by applicant): Our long-range goal is to understand how the neural mechanisms for pursuit and saccadic eye movements operate in health and in various human disease states and how these motor mechanisms are related to higher-level functions. Although pursuit and saccades have long been viewed as distinct motor systems, recent work from our lab and others has shown that certain crucial processing stages are shared. This shared processing likely ensures that pursuit and saccades are properly coordinated with each other and with visual perception and cognition during normal behavior.
The objective of this application is to increase our understanding of this functional overlap. In particular, we will examine the role of the frontal eye fields (FEF) in target selection for pursuit and visual judgments about visual motion, and compare the role of the FEF to that of the superior colliculus (SC). Our primary hypothesis is that some of the neural activity in the FEF is related to general estimates of target position and velocity that are agnostic about the eye motor output; consequently, these signals would be expected to support visual judgments as well as target selection for pursuit and saccades.
The project will address the following three questions: (1) Does the SC contribute to the process of visual discrimination in addition to its role in target selection? (2) Does the FEF play a role in target selection for pursuit, and if so, how does this role compare to its contributions to visual discrimination? (3) Does the FEF contribute to the visual judgments involving motion?
At the completion of this research, we expect to understand how activity in the SC and FEF is related to the mechanisms of target selection for pursuit, as well as saccades, and to have clarified the relationship between target and visual selection involving motion. The relevance of this research to public health. These studies are an important step toward understanding how the brain coordinates the components of voluntary movements and how it establishes and regulates the link between visual processing and motor control. These studies will therefore help refine clinical descriptions of the oculomotor system that are used to diagnose eye movement disorders in humans. Understanding how these systems interact will also help us understand how and why these circuits malfunction in a variety of developmental disorders.
Institution: SALK INSTITUTE FOR BIOLOGICAL STUDIES,
LA JOLLA, CA 920371099
The Journal of Neuroscience, May 15, 2003, 23(10):4333-4344
Neuronal Activity in the Rostral Superior Colliculus Related to the Initiation of Pursuit and Saccadic Eye Movements
Richard J. Krauzlis
Systems Neurobiology Laboratory, Salk Institute for Biological Studies,
La Jolla, California 92037
Under isoflurane anesthesia and aseptic conditions, we attached a head-holder using dental acrylic and titanium screws. The head-holder allowed us to fix the head in the standard stereotaxic position during experiments. During the same surgery, we also implanted a search coil around each eye (Judge et al., 1980 ). The coils were used to monitor eye position with the electromagnetic induction technique (Fuchs and Robinson, 1966 ). After initial behavioral training, we affixed a recording chamber for SC single-neuron recording to the skull in a second surgical procedure. The chamber was angled 38o to the posterior of vertical and directed at the midline, 15 mm above and 1 mm posterior to the inter-aural line.
Neurons identified as rostral buildup neurons were then studied with the gap paradigm illustrated in Figure 2. At the beginning of each experimental trial, the monkey fixated a small spot stimulus (0.2o diameter) that appeared at the center of the display. During this fixation period, which had a randomized duration of 500–1000 msec, the monkey was required to remain within 2o of the central target; otherwise, the fixation spot was extinguished and the paradigm reverted to the fixation period after a 2500 msec timeout. At the end of the fixation period, the central spot was extinguished and a second small spot stimulus appeared at a slightly eccentric location along the horizontal meridian. On pursuit trials, this second stimulus appeared at 2o and moved horizontally toward and through the center of the display at a constant speed of 15o/sec.
The second stimulus appeared either immediately after the offset of the fixation spot (no-gap trials) (Fig. 2 A) or after a delay of 200 msec (gap trials) (Fig. 2C). The small offset in the position of the target stimulus allowed us to elicit pursuit with few or no accompanying saccades (Rashbass, 1961 ), which would have otherwise confounded our analysis of pursuit-related activity. Any pursuit trials containing a saccade in a 600 msec interval beginning 100 msec before target onset were excluded from analysis.
The target stimulus always moved horizontally toward the center of the display, and its starting location was always either inside the response field of the neuron under study or in the opposite hemifield. On saccade trials (Fig. 2 B,D), the second stimulus appeared at 3.5o and remained stationary. Once the second stimulus appeared, the monkey was allowed 500 msec to get its eyes within 3o of the stimulus position and was required to stay within 3o of the target for the remainder of the trial. The monkey was given a liquid reward at the end of each trial performed correctly.
The target on saccade trials was placed at slightly more eccentric locations than on pursuit trials to avoid the increase in saccade latencies and the interference with the gap effect, observed with target eccentricities of 2° (Weber et al., 1992 ; Krauzlis and Miles, 1996b ). As on pursuit trials, the target stimulus was located either within the response field of the neuron under study or in the opposite hemifield.
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