Thesis (Ph. D.)--University of Wisconsin--Madison, 1966. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

This thesis explores the seemingly simple problem of how a rainforest-dwelling primate, Cebus apella libidinosus, manages to survive in the Caatinga dry forest of north-eastern Brazil, a harsh habitat that poses a series of extreme ecological challenges for survival. Albeit a simple question, it unfolds into more complex questions regarding how ecological pressures might drive brain evolution and intelligence in primates. Although there is no "best" hypothesis to explain the evolutionary brain enlargement in higher primates, fine-grained analyses of ecology, such as those presented here provide insights into how different species deal with ecological problems that might require cognitive solutions. Capuchin monkeys are an ideal model for this inquiry. They occupy diverse habitats, and they have proven to be a cognitive puzzle. They are the only monkey to approach great apes in their ability to use tools, but apparently lack the prerequisite mental capability to understand cause and effect. The Caatinga dry forest poses a series of ecological challenges for mammals in general and primates in particular, and these are detailed in this thesis. This is the first general study of mammalian abundance and distribution in Caatinga habitats, with special reference to Cebus. I present several innovative methods for assessing plant and invertebrate biodiversity, as regards foods for the Cebus. The study population of capuchin monkeys faced more frequent and longer periods of food scarcity than does any other known capuchin population. However, the Cebus in the Caatinga circumvent the ecological constraints of low plant food availability through their proficient foraging style (destructive foraging) and through their cognitive abilities, reflected in this population's extensive and intelligent use of technology. I suggest that Old World monkeys and capuchin monkeys have undergone differential selective pressures, with 'Machiavellian intelligence' being a more prominent aspect in the brain evolution of baboons and macaques, while extractive foraging was a more important selective pressure for capuchin monkeys. The evolutionary brain enlargement observed in hominids is suggested to be a legacy of extractive foraging and that capuchin monkeys are excellent models for understanding the factors leading to brain enlargement. This thesis is concluded as an endeavour into understanding the selective forces and concatenation of events that culminated with the evolutionary brain enlargement seen in the hominins.

The study of motor cortex (dorsal premotor cortex and primary motor cortex) has been greatly aided by the development of a conceptual paradigm that has emerged over the past decade. In contrast to established frameworks, which view neural activity within motor cortex as a representation of particular movement parameters, the ‘dynamical systems paradigm’ posits that motor cortex is best understood via the low-dimensional neural processes that allow the generation of motor commands. This framework largely evolved from, and has been most successfully applied to, simple reaching tasks, where the sequential stages of movement generation are largely separated in time – motor cortex absorbs an input that specifies the identity of the upcoming reach, a second input initiates the movement, and strong, autonomous dynamics generate time-varying motor commands. However, while the dynamical systems paradigm has provided a useful scaffolding for interrogating motor cortex, our understanding of the mechanisms that generate movement is still evolving, and many questions remain unanswered. Prior work has established that the neural processes within motor cortex that generate descending commands are initiated by a large, condition-invariant input. But are movements made under different behavioral contexts initiated via the same mechanisms? Lesion studies suggest that the generation of so-called ‘self-initiated movements’ is uniquely dependent on the supplementary motor area (SMA), a premotor region immediately upstream of motor cortex. In contrast, SMA is thought to be less critical for generating externally-cued movements. To characterize the degree to which SMA is able to impact movement initiation across behavioral contexts, we trained two monkeys to make reaches that were either internally or externally cued. On a subset of trials, we disrupted activity within SMA via microstimulation and asked how this perturbation impacted the monkeys’ behavior. Surprisingly, we found that the effect of stimulation was largely preserved across contexts; the behavioral effects of stimulation could be explained by a simple model in which a context-invariant, time-varying kernel multiplicatively altered the odds of movement initiation. These results suggest that SMA is able to impact movement initiation across behavioral contexts. The question of how sequences of discrete actions are generated has been investigated for over one hundred years. It is commonly thought that once a given sequence (particularly a rapid sequence) becomes well-learned, individual actions that were once produced separately become ‘merged’, such that multiple actions are generated as a single, holistic unit. But what does it mean to generate multiple actions as a single unit? The dynamical systems paradigm offers the ability to translate this notion into specific predictions about the timing and structure of neural activity within motor cortex during sequence production. Importantly, it also offers predictions for the alternative hypothesis – that motor cortex generates the component actions of a sequence independently. To determine whether the production of rapid sequences requires motor cortex to merge multiple actions into a single ‘movement’, we trained monkeys to make sequences of two reaches. Surprisingly, we found that the same set of neural events are used to produce rapid sequences and isolated reaches. Rather than merging individual actions into a single unit, motor cortex generated rapid sequences by overlapping the neural activity related to reach preparation and execution. These results demonstrate that the performance of extremely fast, well-learned movement sequences does not require motor cortex to implement a sequence-specific strategy; the same neural motif that produces a simple reach can also generate movement sequences.

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In this thesis, I interpret the meaning of “monkey pots,” a pottery vessel found throughout the Maya world. This study looks at three kinds of monkey pots recovered from the Mirador Basin. Carmelita Incised and Zacatal Polychrome monkey pots date to the Late Classic period (AD 680-800) and were manufactured in the Basin; Telchac Composite monkey pots date to the Terminal Classic period (AD 780-830) and were made in the Usumacinta River region. These monkey pots are described, followed by an analysis and comparison of the function, the monkey genus on the vessels, and the contexts from which the vessels came. I found that each kind of monkey pot functioned as a domestic tool for serving food and later as part of death and burial rituals. The monkeys on the vessels appear to be spider monkeys, which were associated anciently with death and the underworld. Finally, most of the monkey pots were found in burials, implying that they were part of burial rituals. From this information, I suggest that monkey pots assumed meanings associated with death and the underworld when placed in burials. Comparing the function, decoration, and context of these monkey pots implies that their meaning did not change through time and space. I believe the monkey pots demonstrate that some meanings and ideas about death and the underworld endured from the Late to Terminal Classic period in the Mirador Basin and that these meanings may have been shared with people in the Usumacinta River area.

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Thesis (Ph. D.)--University of Chicago, Committee on Neurobiology, March 1999. / Includes bibliographical references. Also available on the Internet.

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