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Our laboratory is currently involved in a wide range of studies that fall into two major areas of research on the mammalian brain. We take a broad interest in the function, connectivity, development, and evolution of complex nervous systems.

1. The primate somatosensory system.

Among the most important behaviors exhibited by humans is the ability to manipulate the world around them with their hands. While most mammals actively explore the world by making fine tactile discriminations with specialized body parts that can manipulate objects of interest, this ability is particularly well developed in primates. Complex manual abilities including tool use is a milestone of our species' history, and the portions of the central nervous system, particularly the neocortex, that participate in the generation of tactile perception, recognition, proprioception, and goal directed reaching are beginning to be understood. Our work examines the contribution of the somatosensory system to the generation of these behaviors.

We appreciate that even for seemingly simple tasks, such as object manipulation and discrimination, inputs from all parts of all digits from both hands must be integrated. In addition, the somatosensory system must provide the motor cortex, posterior parietal cortex, and subcortical structures with relevant information regarding the position of the limbs in space and the location of contact at different points across the hand. The somatosensory system must also provide the motor cortex with feedback regarding changes in the position of the digits of the hand and stimulation patterns across the hand. In this way, exact motor commands specifying how and where to move digits for further exploration can be initiated. We know from previous work that at least nine different cortical areas process inputs from the skin, muscles, and joints. In order to understand the complex interactions of relevant cortical fields and thalamic nuclei, it is critical to understand the details of the circuitry that subserve such functions.

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2. The evolution of complex brains in mammals

We know that mammalian brains differ in size and that mammals with large brains generally have more complex sensory, perceptual, and cognitive behaviors than mammals with small brains. Comparative studies on the organization and connections of the neocortex indicate that size alone is not the source of this variation. Rather, it is the number of functional areas and their connections that are responsible for the remarkable differences in complex behaviors. Fossil records, together with comparative studies, indicate that the first mammals had small brains with very small neocortices and only a few functional areas. Thus, small brains with few parts were the forerunners of the large, complexly organized brains observed in a number of extant mammals.

The following group of studies is designed to determine the processes by which the neocortex becomes more complex. Because we cannot study evolution directly, we examined the products of the evolutionary process which allows us to make inferences about the process. In our comparative studies, we used electrophysiological recording techniques and neuroanatomical tracing techniques in a variety of mammals to examine the functional organization of the neocortex. In this way we can ascertain which features of organization and connection patterns are the same across mammals, due to common ancestry (homologous), and which features are derived. More important, these studies allow us to examine the types of changes in the neocortex that have occurred over the course of evolution and the constraints imposed upon the evolving neocortex. From these experiments, several hypotheses regarding brain evolution have been generated.

Recently we began to test our hypotheses by manipulating aspects of brain development which we believe are occurring naturally in evolution. Our studies of development use genetically altered animals as well as animals in which physical manipulations have been made to specific portions of developing nervous systems.

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