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At least 1,621 records · Page 90Linked to original sources
PubMed2003

A deoxyribozyme-based molecular automaton.

We describe a molecular automaton, called MAYA, which encodes a version of the game of tic-tac-toe and interactively competes against a human opponent. The automaton is a Boolean network of deoxyribozymes that incorporates 23 molecular-scale logic gates and one constitutively active deoxyribozyme arrayed in nine wells (3x3) corresponding to the game board. To make a move, MAYA carries out an analysis of the input oligonucleotide keyed to a particular move by the human opponent and indicates a move by fluorescence signaling in a response well. The cycle of human player input and automaton response continues until there is a draw or a victory for the automaton. The automaton cannot be defeated because it implements a perfect strategy.

Algorithms↗
PubMed2001

Left vagus nerve stimulation with the neurocybernetic prosthesis has complex effects on heart rate and on its variability in humans.

PURPOSE: The purpose of this study was to determine if stimulation of the left vagus nerve (LVNS) with the neurocybernetic prosthesis (NCP) in humans is, as claimed in the literature, without cardiac chronotropic actions. METHODS: We analyzed 228 h of ECG recorded from five subjects with intractable epilepsy who had not benefited from LVNS, for effects on instantaneous heart rate (IHR) and heart rate variability (HRV). RESULTS: There were two main cardiac responses: (a) bradycardia, and (b) tachycardia during the first half, followed by bradycardia during the second half of stimulation (biphasic response). Multiphasic responses characterized by alternating bradycardia and tachycardia were rarely observed. HRV was either increased or decreased depending on the subject and on the stimulation parameters. HRV as a function of HR also showed high interindividual variability, and interestingly, in one case behaved paradoxically, increasing at higher and decreasing at lower heart rates. CONCLUSIONS: LVNS at high intensities has complex effects on IHR and HRV, which show large interindividual variability. These spectra of cardiac responses reflect the interplay of autonomic, visceral, and somatic sensory afferences and the role of central structures in their integration. These findings also point to the need for more comprehensive studies of cardiac function in humans implanted with the NCP, using sensitive methods for data processing and analysis such as those developed for this study.

Adult↗
PubMed1971

Model for constraint and control in biochemical networks.

A model is proposed for biochemical networks which takes into account substrate and modifier effects on enzyme activity and the different time scales on which the relevant processes occur. Sources of global constraint that can be utilized in metabolic regulation are indicated, and the relation of the model to the experiments of Kauffman on switching networks is analyzed. The biological significance of the model and possible systems in which it might be tested are discussed.

Cybernetics↗
PubMed2005

Evolution of the cerebellum as a neuronal machine for Bayesian state estimation.

The cerebellum evolved in association with the electric sense and vestibular sense of the earliest vertebrates. Accurate information provided by these sensory systems would have been essential for precise control of orienting behavior in predation. A simple model shows that individual spikes in electrosensory primary afferent neurons can be interpreted as measurements of prey location. Using this result, I construct a computational neural model in which the spatial distribution of spikes in a secondary electrosensory map forms a Monte Carlo approximation to the Bayesian posterior distribution of prey locations given the sense data. The neural circuit that emerges naturally to perform this task resembles the cerebellar-like hindbrain electrosensory filtering circuitry of sharks and other electrosensory vertebrates. The optimal filtering mechanism can be extended to handle dynamical targets observed from a dynamical platform; that is, to construct an optimal dynamical state estimator using spiking neurons. This may provide a generic model of cerebellar computation. Vertebrate motion-sensing neurons have specific fractional-order dynamical characteristics that allow Bayesian state estimators to be implemented elegantly and efficiently, using simple operations with asynchronous pulses, i.e. spikes. The computational neural models described in this paper represent a novel kind of particle filter, using spikes as particles. The models are specific and make testable predictions about computational mechanisms in cerebellar circuitry, while providing a plausible explanation of cerebellar contributions to aspects of motor control, perception and cognition.

Adaptation, Physiological↗