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contributions to science |
| Sleep (1962-1966) My early work addressed REM patterns of sleep studies. The rapid eye movement phase of sleep is characterized by distinct EEG patterns and by the presence of very large potentials in the pontine reticular formation of cats and other mammals. These potentials occur in conjunction with eye movements, but are not driven by retinal inputs. In collaboration with Dr. Dana Brooks, I discovered that these potentials are transmitted to the lateral geniculate and from there to the visual cortex. These ponto-geniculate-occipital potentials became well known because they were related to the visual imagery of dreams, and were published in Science.
Eye movement coordination (1967-1971) During this period I undertook studies of eye movement coordination. I recorded voluntary eye movements (saccades and tracking) from the frontal eye fields in awake primates, and eye-head coordination in monkeys for evidence of a centrally patterned organization. A significant paper was published in Science dealing with this work. (See Publications.)
Movement in vertebrates (1974 - early 1990s) During this period I undertook a series of studies aimed at understanding the neural control of vertebrate movements. My investigations focused first on understanding the neural, mechanical and geometrical factors underlying the achievements of arm posture. Later, I studied the formation of arm trajectories and formulated the equilibrium point control hypothesis. This work was done in collaboration with N. Hogan.
Motor learning (beginning late 1980s) Beginning in the late 80s, my research was directed at motor learning studies in humans and primates. In humans I investigated the processing of consolidation and vulnerability of motor memories, and motor learning by field approximation. In primates we showed that a distinct population of neurons in the motor cortex changes its pattern of activity as a consequence of learning a new task.
Modularity and rehabilitation (latter 1990s - present) From the latter part of the 90s to the present, a primary focus of my research has centered on modular organization of the motor system: anatomy, physiology and clinical implications. My collaborators and I designed experiments demonstrating that the vertebrate motor system produces movements by combining a small number of units of motor output. Using a variety of approaches such as microstimulation of the spinal cord, NMDA, and iontophoresis, we have provided evidence for a modular organization of the spinal cord. A module is a functional unit in the spinal cord that generates a specific motor output by imposing a specific pattern of muscle activation (muscle synergy). Such an organization might simplify the production of movements by reducing the degrees of freedom that need to be specified.
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