Complex spike patterns in olfactory bulb neuronal networks

Abstract

Using T-pattern analysis, a procedure developed for detecting a particular kind of nonrandomly recurring hierarchical and multi-ordinal real-time sequential patterns (T-patterns), we have inquired whether such patterns of action potentials (spikes) can be extracted from extracellular activity sampled simultaneously from many neurons across the mitral cell layer of the olfactory bulb (OB). Spikes were sampled from urethane-anesthetized rats over a 6 h recording session, or a period lasting as long as permitted by the physiological condition of the animal. Breathing was recorded as markers of peak inhalation and exhalation. Complex t-patterns of up to ~20 elements were identified with functional connections often spanning the full extent of the array. A considerable proportion of these sequences were related to breathing. By comparing sequence detection in our real data with that in the same data when randomized (using either of two procedures, one preserving the interval structure of each spike train, and so the more conservative), we find that the incidence of sequences is very much greater in the real than in the random data. Further, in cases where recordings were terminated before completion of the full recording session, the difference between pattern detection in real data and that of randomized data strongly correlated with the physiological condition of the animal—in recordings leading to the preparation becoming physiologically unstable, the number of patterns detected in real data approached that in the randomized data. We conclude that such sequences are an important physiological property of the neural system studied, and suggest that they may form a basis for encoding sensory information.