An adaptive sensorimotor representation for reaching in the inferior parietal lobule of behaving monkeys

An Adaptive Sensorimotor Representation for Reaching in the Inferior Parietal Lobule of Behaving Monkeys By Anushree Karnik Thesis director: Professor Ralph M. Siegel Primates use visual guidance in order to interact with their environment. For several decades, the inferior parietal lobule (IPL) has been known to contain neurons that respond to visual stimulation and motor behavior. While the neural activity during the reaching behavior has been shown in area 7a of IPL, reach related neural responses have never been tested in the dorsal prelunate area (DP) of IPL, which is adjacent to area 7a. Furthermore, neural response prior to the reaching movement has not been assessed in DP and area 7a. The first aim was to investigate the tuning properties of single neurons in DP and area 7a. The second aim was to assess the influence of eye position signal on reaching behavior. Third, the temporal evolution of sensorimotor transformation in area 7a and DP neurons was investigated by comparing neural signals throughout the reaching task. Lastly, cortical plasticity was tested using Fresnel prisms, which displaced the visual field by 12o in one of four directions: contralateral, ipsilateral, upwards, or downwards. Foveal and peripheral reaching tasks and reaching under perceptually distorted conditions were used. Neurons in area 7a and DP were observed to have differential tuning properties during the planning phase and the initiation of the reach, in addition to being selective for eye position and retinal visual stimulation. The response properties of the neurons in areas 7a and DP changed as the trial progressed in time. Differential preparatory and reach responses were observed during foveal and peripheral reaching. This implies that both eye position and retinal signals modulated the reach related responses. Alterations in spatial tuning of the neurons during all phases of the task were observed upon insertion of the Fresnel prisms imply that neural plasticity occurs as the cortex swiftly adapts to the mismatch between sensory input and motor output. The spatial tuning of the neurons did not merely compensate for the eye position shift implying that signals other than eye position affect the neural response during reaching. These combined results strongly support the claim that crucial aspects of sensorimotor transformation occur in areas 7a and DP. ACKNOWLEDGMENTS The completion of this thesis would have been impossible without the contribution of all the people mentioned below. I extend my greatest gratitude to each and every one of them. First and foremost, I would like to thank my thesis advisor, Prof. Ralph M. Siegel, for providing me with the best guidance, advice, support, and resources. He always encouraged me to set higher goals and just when I thought I had reached my limit, he helped me realize I could extend myself even further. Thank you Ralph for believing in me and allowing me countless opportunities to expand my horizons. Thank you for introducing me to many other leading scientists in our field and providing me with an opportunity to complete a research rotation at Salk! I cannot imagine being able to do that without your support and faith. Thank you for your excellent technical training and your patience when it came to data analysis and especially programming. I cannot thank you enough for your help with securing a post-doctoral position at the Salk Institute! Most importantly, thank you for showing me how interesting and intriguing research is. You are absolutely right – asking questions and coming up with ways to answer them is far more interesting than being in a classroom. Thank you! Thank you! Thank you! I would also like to thank Dr. Barbara Heider for providing me the excellent training in electrophysiology. Thank you, Barbara, for showing me the proper way to conduct experiments (from setup to completion). Thank you for training me in other techniques (e.g.: rat perfusions) and building my confidence even when I made many errors. Thanks a ton for being so patient and for all of your time providing input and advice throughout my thesis project. I also can’t thank you enough for the numerous reviews of this dissertation and all of your suggested edits. You have become more than a colleague, but also a friend. Thank you for all those Swiss chocolates – I will surely miss them. I would also like to thank Jasmine Siegel. You were the best over the past five years. Thank you for teaching me the basics of working with monkeys and training me to handle them. Your confidence in me allowed to me progress even though; I was apprehensive about working with monkeys at times. All those conversations during monkey-business and coffee breaks were awesome. They definitely set a good balance between work and fun while I was in the lab. You have helped me to grow not only as a researcher, but also as a person. I have learned a great deal about culture, psychology, politics, and many other important things in life. I cannot thank you enough for the friendship and the balance that you provided me with throughout graduate school. I would like to thank all the members of the Siegel Lab – past and present. Dr. Milena Raffi: Even though you and I never really worked together, communicating with you about experiments was very helpful. Thank you very much Milena, for providing me with support, advice and understanding that I needed during the initial years of my graduate career. Thank you for hosting me in Italy and giving me an opportunity to present a talk at the University of Bologna. Reuben Meltzer, Sam Kallus, Adam Butensky, and Danny Michaelis– thank you very much for your excellent technical assistance. I cannot imagine completing my experiments without your help. Adam, thank you for providing me with an opportunity to mentor a student; I have learned a great deal