Evolutionary Neurobiology
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Evolutionary Neurobiology
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Katharine L. CampiGraduate Student |
| Main Research Interests: My research is focused on the evolution of the neocortex and how phenotypic variability, in terms of functional map organization and connectivity, emerges in different lineages. My work on the prairie vole (Microtus ochrogaster) has provided important information as a natural model of variation in cortical area organization and connectivity related to lifestyle and behavior. The prairie vole is a good model system for these studies because these rodents have a highly derived lifestyle in that they are among the 3-5% of mammals considered to be socially monogamous. Specifically, I have examined the sensory neocortex in the prairie vole using electrophysiological, histological, and neuroanatomical tracing techniques (Campi et al., 2007). A few interesting findings from these studies emerged. First, that the auditory cortex is larger in the prairie vole when compared to the mouse or the short-tailed opossum and that a large percentage of neocortex is devoted to processing auditory stimuli. Second, that there is multisensory in primary cortical areas. For example, responses to auditory stimuli were observed in the primary somatosensory area (S1) and the primary visual area (V1). Third, that in addition to the traditionally reported cortical and thalamic connections to AC in rodents, direct connections between primary sensory areas are present in the prairie vole, as well as thalamic inputs from non-auditory nuclei. These additional connections form the anatomical substrate for multisensory processing that occurs in the primary sensory areas in the prairie vole. These results are informative to an understanding of the organizational strategies employed for increasing behavioral flexibility in animals with small brains and a small neocortex. Currently, I am examining the functional and architectonic organization of extrastriate cortex using the comparative approach in two species of rodents to better understand the basic mammalian plan of visual cortex organization, and the way in which this plan has been modified to generate visually mediated behaviors associated with the demands of different niches. We will determine the differences in the organization of the visual cortex that are associated with a diurnal versus a nocturnal lifestyle in rodents using wild-caught California ground squirrels (Spermophilus beecheyi) and wild-caught rat (Rattus norvegicus). Individuals of these two species have overlapping ranges in California but very different visual lifestyles and structural visual morphology. The results from these studies will provide insight into the evolution of the visual cortex in rodents, and will be applicable to all studies of diurnal and nocturnal mammals. |
Figure 1. (A) Composite reconstruction of flattened vole cortex illustrating the distribution of responses from electrophysiological recordings and their relationship to architectonically defined primary areas. Neurons in S1 responded primarily to somatosensory stimulation, neurons in V1 responded mostly to visual stimulation and neurons in auditory cortex responded mostly to auditory stimulation. However, multisensory responses can clearly be distinguished within these primary areas as well. When neurons in primary areas and multimodal cortex responded to more than one modality of stimulation, one of the modalities was almost always auditory. Purple dots represent sites in which neurons responded to somatosensory stimuli. Yellow dots represent sites in which neurons responded to visual stimuli. Green dots represent sites in which neurons responded to auditory stimuli. Black dots represent sites in which neurons responded to more than one modality of stimuli. (B) Lightfield, digital image of cortex that has been flattened, sectioned parallel to the cortical surface, and stained for myelin from a different case than that illustrated in A. Although the entire series of sections were used to draw borders, architectonically distinct areas can be visualized even in this single section. Scale bar is 1 mm. Medial is to the top and caudal is to the right. |
Figure 2. A comparison of composite images from the prairie vole, the mouse, and the short-tailed opossum. Primary sensory areas are outlined in black. The primary auditory area is filled with dark gray, and the light gray shading represents the area of cortex in which neurons that respond to auditory stimulation are found. Prairie voles have an enlarged A1 and auditory sensory domain as compared to the other two species. The mean percentage of neocortex devoted to A1 for all three species are given in the table. Data for the mouse is based on Hunt et al., (2006) and data for the opossum is based on Karlen and Krubitzer (2006). |
Figure 3. Summary of connection patterns observed in four rodents. Similar patterns of multisensory connections can be seen in the two socially monogamous rodents. These connections are not present in the promiscuous rodents. The AC of each rodent is represented by the elongated middle box. The boxes above are cortical area connections. The boxes below are thalamic nuclei connections. The thickness of the lines represents the relative amount of connections. |
Journal Articles: Campi KL, Karlen, SJ, Bales, KL, Krubitzer L (2007). Organization in sensory neocortex in prairie voles (Microtus ochrogaster). J Comp Neurol; 502(3):414-26. |
