Speech, writing, and tool-use are all prime examples of everyday learned motor skills that together with dance, music, and sports performance represent the full glory of human cultural expression afforded by dexterous digits, limbs, and bodies. Learning to subconsciously move parts of our body is an underappreciated function of the brain. This dissertation aims to illuminate this process through a series of studies using the zebra finch as a model system. It addresses two major questions. First, what level of modularity is involved in motor learning? Specifically, can we decompose complex learned skills, such as the zebra finch song, into their distinct components such as spectral and temporal aspects? And if so, how independent are these various aspects of motor skill learning and execution from one another? Second, to what degree are the basal ganglia, essential and phylogenetically conserved parts of the motor system, involved in different aspects of motor skill learning? In Chapter 1 of this dissertation, I describe the complex learned vocalization of the zebra finch as a model for understanding these questions, highlighting the use of a rapid and well-controlled learning paradigm termed conditional auditory feedback (CAF). In Chapter 2, using CAF, focal lesions and recordings, I test the role of a songbird basal ganglia pathway in distinct aspects of motor learning. I find that the basal ganglia pathway is necessary for learning spectral but not temporal aspects of the song whereas a pre-motor cortical area encodes changes in the temporal but not spectral structure, suggesting a modularity in birdsong motor learning. In Chapter 3, I infer the mechanisms underlying the basal ganglia-independent temporal learning. Further CAF experiments demonstrate that the nervous system is capable of flexibly modifying temporal structure in one part of the song without affecting the timing in the rest of the song, uncovering yet another level of modularity in encoding song structure. Chapters 2 and 3 provide evidence for the modularity in learning the mean spectral and temporal structure. However, motor performance is also characterized by its trial-to-trial variability around the mean. In Chapter 4, I describe CAF experiments to interrogate the neural basis underlying changes in variability around a mean. I show that spectral variability can be modulated in a very specific manner and independently in different parts of the song. I show that this temporally-specific modulation of variability is mediated by the basal ganglia. Overall, the dissertation suggests that complex motor skills emerge from basic functional modules that independently learn, modulate, and control distinct aspects of learned motor output.
| Identifer | oai:union.ndltd.org:harvard.edu/oai:dash.harvard.edu:1/13070035 |
| Date | January 2014 |
| Creators | Ali, Farhan |
| Contributors | Olveczky, Bence P |
| Publisher | Harvard University |
| Source Sets | Harvard University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis or Dissertation |
| Rights | closed access |
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