In awake rodents, the neural representation of olfactory information in the olfactory bulb is largely dependent on brain state and behavioral context. Learning-modified neural plasticity has been observed in mitral/tufted cells, the main output neurons of the olfactory bulb. Here, we propose that the odor information encoded by mitral/tufted cell responses in awake mice is highly dependent on the behavioral task demands. We used fiber photometry to record calcium signals from the mitral/tufted cell population in awake, head-fixed male mice under different task demands. We found that the mitral/tufted cell population showed similar responses to two distinct odors when the odors were presented in the context of a go/go task, in which the mice received a water reward regardless of the identity of the odor presented. However, when the same odors were presented in a go/no-go task, in which one odor was rewarded and the other was not, then the mitral cell population responded very differently to the two odors, characterized by a robust reduction in the response to the nonrewarded odor. Thus, the representation of odors in the mitral/tufted cell population depends on whether the task requires discrimination of the odors. Strikingly, downstream of the olfactory bulb, pyramidal neurons in the posterior piriform cortex also displayed a task-demand-dependent neural representation of odors, but the anterior piriform cortex did not, indicating that these two important higher olfactory centers use different strategies for neural representation.

Synchronized oscillations are of critical functional importance in many biological systems. We show that such oscillations can arise without centralized coordination in a disordered system of electrically coupled excitable and passive cells. Increasing the coupling strength results in waves that lead to coherent periodic activity, exhibiting cluster, local and global synchronization under different conditions. Our results may explain the self-organized transition in a pregnant uterus from transient, localized activity initially to system-wide coherent excitations just before delivery. [2][3][4][5]. Synchronization of spatially distributed oscillators is of crucial importance for many biological systems [6]. For example, disruption of coherent collective activity in the heart can result in life-threatening arrhythmia [7]. In several cases, the rhythmic behavior of the entire system is centrally organized by a specialized group of oscillators (often referred to as pacemakers) [8] as in the heart, where this function is performed in the sino-atrial node [9]. However, no such special coordinating agency has been identified for many biological processes. A promising mechanism for the self-organized emergence of coherence is through coupling among neighboring elements. Indeed, local interactions can lead to order without an organizing center in a broad class of complex systems [10].The present work is inspired by studies of the pregnant uterus whose principal function is critically dependent on coherent rhythmic contractions that, unlike the heart, do not appear to be centrally coordinated from a localized group of pacemaker cells [11]. In fact, the uterus remains quiescent almost throughout pregnancy until at the very late stage when large sustained periodic activity is observed immediately preceding the expulsion of the fetus [12]. In the USA, in more than 10 % of all pregnancies, rhythmic contractions are initiated significantly earlier, causing preterm births [13], which are responsible for more than a third of all infant deaths [14]. The causes of premature rhythmic activity are not well understood and at present there is no effective treatment for preterm labor [12].In this paper we have investigated the emergence of coherence using a modeling approach that stresses the role of coupling in a system of heterogeneous entities. Importantly, recent studies have not revealed the presence of pacemaker cells in the uterus [15]. The uterine tissue has a heterogeneous composition, comprising electrically excitable smooth muscle cells (uterine myocytes), as well as electrically passive cells (fibroblasts and interstitial Cajal-like cells [ICLCs]) [16,17]. Cells are coupled in tissue by gap junctions that serve as electrical conductors. In the uterine tissue, the gap junctional couplings have been seen to markedly increase during late pregnancy and labor, both in terms of the number of such junctions and their conductances (by an order of magnitude [18]), which is the most striking of all electrophysiological changes the ...