My long-term research interests center around understanding the physiological mechanisms underlying the functional and computational properties brain neuronal networks. These mechanisms are best elucidated by detailed studies of the physiological properties of the synapses, cells and circuits involved in the performance of a given task. In particular, I am interested in how phenomena such as dendritic integration and synaptic plasticity may allow small groups of neurons to perform complex functions. Understanding such computational properties of brain networks often requires the simultaneous acquisition of data from several cells within a network and/or from multiple locations within a single cell. Thus, I also am interested in the application and development of physiological and optical techniques that facilitate this sort of parallel data acquisition in vitro and in vivo.

My current interests center on understanding how the circuitry of the olfactory bulb transforms the spatially segregated, rate-coded and combinatorial glomerular odor representation, into a representation that is more spatially homogenous, more sparse and which may depend on the precise timing of mitral cell spikes. In particular I want to understand how this transformation is implemented in the circuitry of the bulb. One prevailing idea is that the circuitry of the olfactory bulb is functionally similar to the circuitry found in the retina and in parts of the neocortex in that it performs a kind of "lateral inhibition". On this view activation of a given mitral cell should result in inhibition of neighboring mitral cells. However, unlike visual stimuli, olfactory stimuli are not intrinsically spatial in nature. Moreover, it is not clear that similar odors are mapped onto nearby regions of the bulb which makes it difficult to understand how lateral inhibition is implemented by bulb circuitry.

Recently, I have been working to describe the lateral spread of inhibition and excitation within the network of the mitral and tufted cells, which are the output neurons of the olfactory bulb. Whole cell and optical recordings from mitral cell dendrites have allowed me to examine activity-dependent short term changes in recurrent and lateral inhibition that might underlie variations in odor-evoked activity that we observe on the time scale of seconds. I have described how these processes underlie the competitive interactions between mitral cells and how they shape odor representations at the level of the olfactory bulb.

Arevian AC, Kapoor V, Urban NN. 2008. Dynamic Gating of Lateral inhibition in the Olfactory Bulb. Nature Neuroscience. January 2008. (in press).

Ermentrout GB, Galán RF, Urban NN. 2007. Relating neural dynamics to neural coding. Physical Review Letters. (in press).

Bagley J, LaRocca G, Jimenez DA, Urban NN. 2007. Adult neurogenesis and specific replacement of interneuron subtypes in the mouse main olfactory bulb. BMC Neuroscience 8(1):92 (Epub ahead of print)

Castro JB, Hovis KR, Urban NN. 2007. Recurrent dendrodendritic inhibition of accessory olfactory bulb mitral cells requires activation of group I metabotropic glutamate receptors. J. Neurosci. 27(21):5664-71.

Kapoor V, Urban NN. 2006. Glomerulus-specific, long latency activity in the olfactory bulb granule-cell network. J. Neuroscience. 26(45):11709-19.

Galán RF, Fourcaud-Trocme N, Ermentrout GB, Urban NN. 2006. Correlation-induced synchronization of oscillations in olfactory bulb neurons. J. Neuroscience, 26(14):3646-55.

Fernández Galán R, Ermentrout GB, Urban NN. 2005. Efficient estimation of phase-resetting curves in real neurons and its significance for neural-network modeling. Phys Rev Lett. Apr 22;94(15):158101.