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Sensory Information Processing in the Behaving Animal
Summary: Dmitry Rinberg's research is aimed at deciphering the olfactory code and revealing the underlying neuronal mechanisms in the behaving animal.
Until now, most of our knowledge of the function and organization of sensory systems has been obtained in anesthetized preparations. However, the recording of neuronal activity in awake and freely moving animals is of critical importance, since sensory information processing, even at the early stages, is modulated by fully active feedback from other brain areas, learning-related changes in neural representation of a stimulus can be recorded in real time, and specific quantifiable behaviors can be used to interpret the outcome of information processing. The power of combining psychophysical and neurophysiological methods has been demonstrated in the study of visual information processing, especially in primates. As a model organism, mice permit the use of modern genetic tools to monitor, modify, and control brain circuits. Using a mouse to study sensory information processing naturally leads to focusing on olfaction due to its high relevance to rodent behavior.
Very little is known about the processing of olfactory information in a freely moving mouse because of the technical challenges associated with neurophysiological recording in a small, highly mobile animal. Our recent experiments directly demonstrated that sensory information processing in a behaving animal is, indeed, qualitatively different from that in an anesthetized preparation.
Odor Representation in the Awake Mouse
In our previous work, we found a striking difference in odor responses between the awake and anesthetized state. The odor response of mitral cells in an awake mouse is much sparser than that in an anesthetized animal. These differences are so dramatic that the firing rate in awake mice could not be predicted based on extrapolation from studies in anesthetized animals. This discovery leads to fundamental rethinking of the principles of coding and processing of olfactory information. Sparseness and strong spatial heterogeneity of the odor responses create a challenge with regard to adequate sampling of odor and cell space. We are developing experimental paradigms for efficient cell and odor space sampling in the behaving mouse. The simultaneous recording of multicellular activity and local field potential will provide information for characterization of different modes of information transmission from the olfactory bulb to the cortex.
The Role of Learning in Odor Coding
Our preliminary studies and previous work indicated that mitral cell odor responses are modulated by learning. We have developed a behavioral paradigm that allows us to establish a new odor association during a single behavioral session. Tracking of neuronal odor responses during the time when the new odor-reward association is being established will reveal the role of learning in odor coding.
The Mechanisms of Olfactory Object Recognition
Our studies showed that mitral cells are the first recipients of olfactory information after odor receptors modulate their activity, even before a mouse is exposed to an odor stimulus. The studies of others in humans have shown that imagining smells can cause sniffing. We hypothesize that activation of the olfactory bulb, via either cortical feedback or motor activity (sniffing), may participate in the representation of an olfactory object. We are developing methods to quantify both the neuronal and behavioral responses to find neural correlates of olfactory object recognition. We are also developing methods to quantify which features of the neuronal signal are correlated with the stimulus and which features are correlated with behavior.
These goals require us to develop new methods of data acquisition and data analysis. While initially our laboratory is focused on multielectrode multineuronal recording in the awake, freely moving mouse, our next step is to develop optical methods of recording multineuronal activity, in collaboration with other laboratories at Janelia Farm.
Last updated: September 6, 2006
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