ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY Volume 15, Number 4, 2012, 301–318 Control Languages Associated with Spiking Neural P Systems Ajeesh RAMANUJAN, Kamala KRITHIVASAN Department of Computer Science and Engineering, Indian Institute of Technology Madras, Chennai - 36 E-mail: ajeeshramanujan@gmail.com, kamala@iitm.ac.in Abstract. We consider labeled spiking neural P systems, which are usual spiking neural P systems with a label associated with every rule; the labels are symbols of a given alphabet or can be λ (empty). The rules used in a transition should have either the empty label or the same label from the chosen alphabet. In this way, a string is associated with each halting computation, called the control word of the computation. The set of all control words associated with computations in a given spiking neural P system form the control language of the system. We study the family of control languages of spiking neural P systems in com- parison with the families of finite, regular, context-free, context-sensitive, and recursively enumerable languages. In the restricted case when in each step at least one rule with a non-empty label is used, every regular language is a control language, there are context-sensitive non-context-free languages of this type, but not all context-free languages are control languages of a spiking neural P system. All languages that are accepted by labeled spiking neural P systems are context-sensitive. If transitions with all rules labeled with λ are allowed, then each recursively enumerable language can be the control word of a spiking neural P system. 1. Introduction Spiking neural P systems (shortly called SN P systems) are distributed parallel computing devices introduced in [1] as a class of membrane systems (also known as P systems) [3, 2] inspired by the neurophysiological behavior of neurons sending electrical impulses (spikes) along axons to other neurons. In SN P systems, the