Neural mechanisms and dynamics underlying reaching and decision making

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The ultimate purpose of the motor system is clear: it exists to control the body. However, despite the motor system being among the longest-studied brain structures, it remains unclear how -- mechanistically -- motor cortex performs this function. Here, a mechanistic approach was taken to investigate how primary motor cortex (M1) and dorsal premotor cortex (PMd) control movement. That is, the goal was to elucidate the dynamics of the motor cortex 'machine.' Monkeys were trained in reaching tasks, and neural signals were recorded from their brains as they performed them. Two broad classes of analysis were used. First, cell-by-cell analyses were combined with cell-type analyses, which permitted examining the activity patterns of excitatory and inhibitory neurons separately. Second, techniques based on dynamical systems analysis (such as dimensionality reduction) were applied, which permitted analysis of neural populations as a whole and abstraction to a somewhat higher level of system function. Three major results and a technical advance are presented. Firstly, we investigated how it is possible for an animal to hold still even as neural activity in motor cortex changes drastically during preparation for the upcoming movement. We found that, contrary to common assumptions, there does not appear to be a 'gate' comprised of high inhibition during preparation. Instead, using the dynamical systems perspective, we found that preparatory activity has a special structure such that it remains in intrinsically muscle neutral, 'iso-force' patterns. Secondly, we searched for coherent dynamics in the movement-time activity of motor cortex. We found that motor cortex appears to obey a relatively simple set of dynamics, dominated by oscillatory patterns. Moreover, the exact neural trajectory is heavily determined ('seeded') by the immediately preceding preparatory activity. In order to causally perturb these dynamics with patterned stimulation and cell-type specificity, we then developed a set of optogenetic techniques for use in primates. Finally, we investigated how the dynamics of the decision-making process are reflected in motor cortex. To do so, we combined a novel decision-making paradigm, many simultaneous neural recordings, and single-trial analytical techniques. Preliminary results are given for this final section, demonstrating the presence of vacillation in monkey decision-making. In summary, we found that preparation and movement can be understood as an oscillatory dynamical system seeded by preparatory activity that lives in an iso-force space, that inhibitory and excitatory neurons seem to play more similar roles in the dynamical system than might be expected, and that moment-by-moment processes of motor decision-making can be seen in motor cortex.


Type of resource text
Form electronic; electronic resource; remote
Extent 1 online resource.
Publication date 2011
Issuance monographic
Language English


Associated with Kaufman, Matthew Tyler
Associated with Stanford University, Department of Neurosciences.
Primary advisor Shenoy, Krishna V. (Krishna Vaughn)
Thesis advisor Shenoy, Krishna V. (Krishna Vaughn)
Thesis advisor Huguenard, John
Thesis advisor Knudsen, Eric I
Thesis advisor Moore, Tirin, 1969-
Advisor Huguenard, John
Advisor Knudsen, Eric I
Advisor Moore, Tirin, 1969-


Genre Theses

Bibliographic information

Statement of responsibility Matthew T. Kaufman.
Note Submitted to the Department of Neurosciences.
Thesis Ph.D. Stanford University 2011
Location electronic resource

Access conditions

© 2011 by Matthew Tyler Kaufman

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