Urban Lab Research Activities
Currently, work in my lab focuses on understanding the physiological mechanisms underlying the functional and computational properties of brain neuronal networks, focusing on the olfactory system. In particular, I am interested in describing the detailed anatomical and physiological properties of cells and synapses, and then constructing models that provide insight into how these physiological properties give rise to the functional circuits that transform and store information in the brain. My goal is to use these models to get at the underlying computations that these physiological systems can be seen as implementing.
Here I outline the main lines of research currently going on in my lab, providing some detail about the issues that we seek to address and about the approaches we are taking.
Outline of research
Lateral inhibition in the main olfactory system. The working hypothesis of this work is that inhibitory interactions between nearby mitral cells can be seen as suppressing particular signals, allowing neurons to engage in a sort of local competition. This competition results in some signals being suppressed or filtered, while others pass through to the cortex. In particular, by combinations of paired whole cell recording and calcium imaging we have shown that the competitive inhibitory interactions between mitral cells are temporally specific (Kapoor and Urban, 2006) spatially/anatomically constrained (Egger and Urban, 2006) and activity-dependent (Arevian Kapoor and Urban, 2008). We also have shown that activity-dependent lateral inhibition produces time-dependent decorrelation of activity patterns in a manner that does not require spatial structure. We are investigating these algorithms for a variety of applications
Neuronal synchronization and reliability. Simultaneous firing, especially oscillatory firing, is a common feature of brain activity in many areas and across many species. We are interested in uncovering biophysical and computational mechanisms of such synchronization in the olfactory system. This work involves the combination of computational and physiological approaches to determine which aspects of neuronal dynamics, synaptic properties and anatomical connectivity are critical for the generation of synchronized activity (Galan et al., 2005). We also have described a novel mechanism of synchronization in neurons whereby increased levels of aperiodic “noisy” inputs enhance the synchronized oscillatory firing of olfactory bulb mitral cells (Galan et al., 2006). We are generally interested in tehse constructive effects of noisy inputs (Ermentrout, Galan Urban 2008.)
Single neuron and circuit level integration in the accessory olfactory system. In the accessory olfactory system our work has focused on understanding how the accessory olfactory bulb neurons maintain high levels of both sensitivity and selectivity in their response properties. Our working hypothesis is that the response of cells in the accessory olfactory bulb is influenced by local hotspots of activity in their dendritic trees. These local hotspots of activity allow input to be integrated in a highly non-linear fashion and thus to respond with high fidelity to low concentration stimuli (Urban and Castro, 2005). Further work is centered around the linkage between dendritic excitability and neurotransmitter release ion the accessory olfactory bulb (Castro and Urban in revision). We also are interested in how AOB circuits integrate activity arriving in multiple glomeruli
Learning and neurogenesis in the olfactory system. Finally, we are also pursuing questions related to the relationship between adult neurogenesis and olfactory learning. Several subtypes of olfactory bulb interneurons are known to be replaced throughout life. We are seeking to determine whether the rate or subtype specificity of neuronal replacement is altered by activity. This work involves the use of viral vectors to label and alter the activity of small numbers of adult-born neurons (Bagley et al 2008).
MEG studies of attention and decision making. We recently have begun using magnetoencephalography to identify brain areas that are engaged in synchronous activity during attention and decision making tasks in human subjects. This work attempts to apply our understanding of the mechanisms of synchronous oscillations to questions related to functional properties of synchronous activity within and between brain areas.