We study the dynamics of excitable integrate-and-fire neurons in a small-world network. At low densities p of directed random connections, a localized transient stimulus results in either selfsustained persistent activity or in a brief transient followed by failure. Averages over the quenched ensemble reveal that the probability of failure changes from 0 to 1 over a narrow range in p; this failure transition can be described analytically through an extension of an existing mean-field result. Exceedingly long transients emerge at higher densities p; their activity patterns are disordered, in contrast to the mostly periodic persistent patterns observed at low p. The times at which such patterns die out are consistent with a stretched-exponential distribution, which depends sensitively on the propagation velocity of the excitation.PACS numbers: 87.18.Sn,87.10.+e Recent research in complex networks has provided increasing evidence for their relevance to a variety of physical, biological, and social phenomena [1,2,3]. Two distinct types of topology have been particularly useful in providing insights into the implications of complex connectivity: scale-free networks [3], characterized by the existence of a small number of hubs with high coordination number, and small-world networks [1], characterized by the presence of shortcuts that link two randomly chosen sites regardless of the distance between them.So far, most work on complex networks has focused on their topological and geometrical properties; less attention has been given to the properties of dynamical systems defined on such networks. The interplay between the intrinsic dynamics of the constituent elements and their complex pattern of connectivity strongly affects the collective dynamics of the resulting system. For instance, the addition of shortcuts induces a finite-temperature phase transition even in the one-dimensional Ising model [4] and the introduction of unidirectional shortcuts can change the second-order phase transition in the twodimensional Ising model into a first-order one [5]. In a system of coupled oscillatory elements, the introduction of shortcuts enhances synchronization [6], while the introduction of hubs eliminates the threshold for epidemic propagation [7].The coexistence of shortcuts and regular local connections characteristic of small-world networks (SWNs) mimics a salient feature of the circuitry in the cortex [8,9,10,11,12,13], where experimental observations of excitatory traveling waves [11] provide evidence of some degree of local connectivity, while it is also recognized that long-range excitatory connections are present [10,12]. Our goal is to explore the influence of this complex connectivity on the dynamics of neuronal circuits; to this purpose, we choose a minimal model. The underlying network is modeled as a SWN with unidirectional shortcuts that reflect the nonreciprocal character of synaptic connections, and the excitable neurons are modeled as leaky integrate-and-fire units. We find that even this simple model exhibi...