Faculty Bibliography

Responses of mitral cells represent the results of the first stage of odor processing in the olfactory bulb. Most of our knowledge about mitral cell activity has been obtained from recordings in anesthetized animals. We compared odor-elicited changes in firing rate of mitral cells in awake behaving mice and in anesthetized mice. We show that odor-elicited changes in mitral cell firing rate were larger and more frequently observed in the anesthetized than in the awake condition. Only 27% of mitral cells that showed a response to odors in the anesthetized state were also odor responsive in the awake state. The amplitude of their response in the awake state was smaller, and some of the responses changed sign compared with their responses in the anesthetized state. The odor representation in the olfactory bulb is therefore sparser in awake behaving mice than in anesthetized preparations. A qualitative explanation of the mechanism responsible for this phenomenon is proposed.

The basic psychophysical principle of speed-accuracy tradeoff (SAT) has been used to understand key aspects of neuronal information processing in vision and audition, but the principle of SAT is still debated in olfaction. In this study we present the direct observation of SAT in olfaction. We developed a behavioral paradigm for mice in which both the duration of odorant sampling and the difficulty of the odor discrimination task were controlled by the experimenter. We observed that the accuracy of odor discrimination increases with the duration of imposed odorant sampling, and that the rate of this increase is slower for harder tasks. We also present a unifying picture of two previous, seemingly disparate experiments on timing of odorant sampling in odor discrimination tasks. The presence of SAT in olfaction provides strong evidence for temporal integration in olfaction and puts a constraint on models of olfactory processing.

More than 50 years have passed since the first recording of neuronal responses to an odor stimulus from the primary olfactory brain area, the main olfactory bulb. During this time very little progress has been achieved in understanding neuronal dynamics in the olfactory bulb in awake behaving animals, which is very different from that in anesthetized preparations. In this paper we formulate a new framework containing the main reasons for studying olfactory neuronal dynamics in awake animals and review advances in the field within this new framework.

Nervous systems often face the problem of classifying stimuli and making decisions based on these classifications. The neurons involved in these tasks can be characterized as sensory or motor, according to their correlation with sensory stimulus or motor response. In this study we define a third class of neurons responsible for making perceptual decisions. Our mathematical formalism enables the weighting of neuronal units according to their contribution to decision making, thus narrowing the field for more detailed studies of underlying mechanisms. We develop two definitions of a contribution to decision making. The first definition states that decision making activity can be found at the points of emergence for behavioral correlations in the system. The second definition involves the study of propagation of noise in the network. The latter definition is shown to be equivalent to the first one in the cases when they can be compared. Our results suggest a new approach to analyzing decision making networks.

A pneumatic gun for ballistic delivery of microparticles to soft targets is proposed and demonstrated. The particles are accelerated by a high-speed flow of helium in a capillary tube. Vacuum suction applied to a concentric larger diameter tube is used to divert substantially all of the flow of helium from the gun nozzle, thereby preventing the gas from hitting and damaging the target. Speed of ejection of micron-sized gold particles from the gun nozzle, and their depth of penetration into agarose gels are reported. (c) 2005 American Institute of Physics

Experiments on the cercal wind-sensing system of the American cockroach, Periplaneta americana, showed that the firing rate of the interneurons coding wind information depends on the bandwidth of random noise wind stimuli. The firing rate was shown to increase with decreases in the stimulus bandwidth, and be independent of changes in the total power of the stimulus with constant spectral composition. A detailed analysis of ethologically relevant stimulus parameters is presented. A phenomenological model of these relationships and their relevance to wind-mediated cockroach behavior is proposed.