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On the Power of P Systems with DNA-Worm-Objects

100%

Maté J. L. , Rodriguez-Patón A. , Silva A.

2002

tom Vol. 49, nr 1-3

229-239

We introduce a variant of P systems with string-objects - called worm-objects - inspired in the DNA computing area. These systems work with multisets of string-objects processed by splitting, mutation, replication and recombination. This model is simpler (we eliminate the replication operation) and more realistic (the recombination operation is changed by the simpler one of suffix-prefix or head-tail concatenation developed in the DNA computing framework) than the previous one. The result of a computation is the set of strings sent out of the system. We work with multisets of strings but we generate languages instead of sets of numbers. We prove that, without priority among rules or other control mechanisms, (1) these P systems with at most three membranes can generate all recursively enumerable languages, (2) with non-decreasing length mutation and splitting rules, three membranes are enough to generate the family of context-sensitive languages, and (3) with these restricted types of splitting and mutation rules, four membranes can generate the family of recursively enumerable languages.

Stimulus dependent oscillations in visually evoked activity of cat's superior colliculus

88%

Foik A. , Silva A. , Wypych M. , Mochol G. , Waleszczyk W. J.

tom 72

nr 2

Visual information is transferred from retina to higher order cortical areas by few parallel pathways and encoded in different ways. In this study, we focused on encoding of visual information in the superior colliculus, which is the first stage of extrageniculate pathway. One of ways in which neurons encode information is rate coding based on the change in a number of action potentials in response to stimulus presentation. The other coding scheme is temporal coding, which include information about temporal patterns of neuronal spiking, present, for example, in the form of oscillations. The aim of this study was to reveal the presence of stimulus dependent oscillations in visually evoked activity of neurons in the superficial layers of the cat’s superior colliculus. Neuronal activity was recorded from anesthetized (isoflurane in N2O/O2) animals during visual stimulation by spot of light moving in broad range of velocities as well as during presentation of light spot flashing in random locations within the receptive field of recorded neuron. Oscillations were identified by means of auto-correlation and spectral analyses. We found stimulus dependent oscillations in half of tested neurons. Moreover, oscillatory activity appeared to depend on the stimulus velocity. Different measures of oscillations strength (SO), such as z-score, oscillation score or F-statistics revealed positive correlation between SO and velocity. Stimulus dependent oscillations appeared also in responses to onset of the light spot. These results suggest importance of oscillations for processing of information about fast changes within receptive fields of neurons in the extrageniculate pathway. Supposedly presence of oscillations in responses of collicular cells can increase probability of information transfer to higher level of visual processing. Supported by NCN grant N N303 820640.