For many behaviors we rely on our senses, which inform the brain about the world around us, such as the spatial location of an object we would like to grasp or the motion of a target that we intend to follow with our eyes. In order to execute an appropriate movement, neural responses in sensory areas must be read out and transformed into signals meaningful to premotor and motor areas so an accurate motor command can evolve. I used smooth pursuit eye movements to study the sensory-motor transformation of visual signals about object motion into an appropriate motor command for accelerating the eyes. I found that fluctuations in single neuron responses in visual area MT are predictive of deviations in eye speed during pursuit initiation, which suggests that responses in MT contribute to noise in the motor output. Further, the relationship between the sensory and motor variability revealed constraints about the neural mechanisms underlying the transformation of MT signals into a command for eye speed: if downstream noise is low, a modified vector averaging computation involving opponent signals between oppositely tuned neurons could explain the relationship between responses of single neurons in area MT and eye speed at the initiation of pursuit.
In addition to smooth pursuit eye movements, we studied MT responses during drifts in eye movements of fixation. I found that deviations in sensory responses not only predict variation in pursuit initiation, but that deviations in eye velocity during fixation also modulate the neural responses in MT. I showed that firing rates in MT are modulated because tiny changes in eye velocity generate image motion on the retina. These results demonstrate that image motion due to miniature eye movements is large enough to affect the responses of visual neurons beyond the retina or early cortical visual areas.
This thesis has underscored how tightly sensory and motor systems are interwoven; visual area MT, in particular, forms an important link between the processing of visual signals and the generation of motor commands for smooth pursuit eye movements.
|Advisor:||Lisberger, Stephen G.|
|Commitee:||Dan, Yang, Doupe, Allison J., Sabes, Philip N., Schreiner, Christoph E.|
|School:||University of California, San Francisco|
|School Location:||United States -- California|
|Source:||DAI-B 72/09, Dissertation Abstracts International|
|Keywords:||Eye movements, Fixation, Neuron-behavior correlations, Oculomotor behavior, Sensory-motor, Smooth pursuit, Visual area MT|
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