Faculty Bibliography

Sleep plays an active role in memory consolidation. Sleep structure (REM/ Slow-wave sleep [SWS]) is modified after conditioning, and in some cortical circuits, SWS is associated with replay of the learned experience. Interestingly, the sleep modifications can be local, only affecting activity in the brain regions active during the training. Here, we wanted to ascertain possible changes in sleep structure within olfactory cortex following odor fear conditioning. We recorded local field potentials (LFP) from the anterior piriform cortex (aPCX) in behaving animals and analyzed odor-evoked changes during fear conditioning and subsequent sleep structure modifications. Long-Evans hooded rats were chronically implanted with telemetry electrodes in the aPCX. Rats were placed in a conditioning box for 30 min on three baseline days, conditioned with ten paired odor-shock stimuli on the fourth day, and tested with five odor pulses on the fifth day. On the conditioning and test days, behavioral (freezing or vocalization), autonomic (heart rate) and LFP responses to the conditioned odor were examined. After each daily session, we placed the animal in a dark, sound attenuating chamber and recorded LFPs and EMG for 4 hours. Preliminary data show that rats learned behavioral and autonomic fear responses to the odor and that aPCX odor-evoked beta (15-40 Hz) oscillatory activity may correlate with the magnitude of the fear response. Furthermore, aPCX SWS increased following odor-shock conditioning compared to baseline days. Unpaired control rats showed neither odor fear responses nor an increase in SWS. Finally, the activity of aPCX single-units during SWS was shaped by recent odor experience and there was enhanced functional connectivity between the aPCX and hippocampus during SWS compared to other period

The most commonly cited descriptions of the behavioral characteristics of habituation come from two papers published almost 40 years ago [Groves, P. M., & Thompson, R. F. (1970). Habituation: A dual-process theory. Psychological Review, 77, 419-450; Thompson, R. F., & Spencer, W. A. (1966). Habituation: A model phenomenon for the study of neuronal substrates of behavior. Psychological Review, 73, 16-43]. In August 2007, the authors of this review, who study habituation in a wide range of species and paradigms, met to discuss their work on habituation and to revisit and refine the characteristics of habituation. This review offers a re-evaluation of the characteristics of habituation in light of these discussions. We made substantial changes to only a few of the characteristics, usually to add new information and expand upon the description rather than to substantially alter the original point

Olfaction represents an ideal model system for the study of mammalian habituation given that it is an anatomically relatively simple system with strong reciprocal connections to the limbic system, driving both reflexive and non-reflexive (motivated) behaviors that are easily quantifiable. Data are reviewed here demonstrating short-term habituation of the odor-evoked heart-rate orienting reflex described according to the criteria for habituation outlined by Thompson and Spencer [Thompson, R. F., & Spencer, W. A. (1966). Habituation: A model phenomenon for the study of neuronal substrates of behavior. Psychological Reviews, 73(1), 16-43]. A necessary and sufficient mechanism of short-term habituation is then described, which involves a metabotropic glutamate receptor mediated depression of afferent input to the piriform (primary olfactory) cortex. Finally, evidence for, and a mechanisms of, dishabituation of the orienting reflex and cortical adaptation are described

The nervous system must provide a mechanism for very precise discrimination of differing patterns of activity, yet at the same time, there must be a mechanism for generalization to prevent all experiences from being independent and novel. Pattern separation and completion by cortical circuits contribute to these processes, respectively. Based on theoretical and computational models of the piriform cortex and experimental designs developed for hippocampal spatial memory, we provide evidence for pattern separation and completion in the olfactory system and demonstrate the predictive power of these two processes for behavioral odor perception

The 31st Annual Association for Chemoreception Sciences (AChemS) met in Sarasota, Florida April 22-26, 2009, attracting approximately 600 registrants and nearly 400 abstracts. In addition to poster and platform presentations, the program offered symposia, special lectures, and various National Institutes of Health (NIH)-sponsored workshops, including one on computational approaches to olfaction

Dishabituation is a return of a habituated response if context or contingency changes. In the mammalian olfactory system, metabotropic glutamate receptor mediated synaptic depression of cortical afferents underlies short-term habituation to odors. It was hypothesized that a known antagonistic interaction between these receptors and norepinephrine ss-receptors provides a mechanism for dishabituation. The results demonstrate that a 108 dB siren induces a two-fold increase in norepinephrine content in the piriform cortex. The same auditory stimulus induces dishabituation of odor-evoked heart rate orienting bradycardia responses in awake rats. Finally, blockade of piriform cortical norepinephrine ss-receptors with bilateral intracortical infusions of propranolol (100 microM) disrupts auditory-induced dishabituation of odor-evoked bradycardia responses. These results provide a cortical mechanism for a return of habituated sensory responses following a cross-modal alerting stimulus