18 June 2007

Liberul arbitru la musculitele de otet

Un studiu arata ca musculitele de otet au un comportament atat nedeterminist cat si nealeator.
The researchers tethered fruit flies (Drosophila melanogaster) in completely uniform white surroundings and recorded their turning behavior. In this setup, the flies do not receive any visual cues from the environment and since they are fixed in space, their turning attempts have no effect. Thus lacking any input, their behavior should resemble random noise, similar to a radio tuned between stations. However, the analysis showed that the temporal structure of fly behavior is very different from random noise. The researchers then tested a plethora of increasingly complex random computer models, all of which failed to adequately model fly behavior. Only after the team analyzed the fly behavior with methods developed by co-authors George Sugihara and Chih-hao Hsieh from the Scripps Institution of Oceanography at UC San Diego did they realize the origin of the fly's peculiar spontaneity. "We found that there must be an evolved function in the fly brain which leads to spontaneous variations in fly behavior" Sugihara said. "The results of our analysis indicate a mechanism which might be common to many other animals and could form the biological foundation for what we experience as free will".
Comunicatul de presa Articolul original Filmulet explicativ Abstractul:
Brains are usually described as input/output systems: they transform sensory input into motor output. However, the motor output of brains (behavior) is notoriously variable, even under identical sensory conditions. The question of whether this behavioral variability merely reflects residual deviations due to extrinsic random noise in such otherwise deterministic systems or an intrinsic, adaptive indeterminacy trait is central for the basic understanding of brain function. Instead of random noise, we find a fractal order (resembling Lévy flights) in the temporal structure of spontaneous flight maneuvers in tethered Drosophila fruit flies. Lévy-like probabilistic behavior patterns are evolutionarily conserved, suggesting a general neural mechanism underlying spontaneous behavior. Drosophila can produce these patterns endogenously, without any external cues. The fly's behavior is controlled by brain circuits which operate as a nonlinear system with unstable dynamics far from equilibrium. These findings suggest that both general models of brain function and autonomous agents ought to include biologically relevant nonlinear, endogenous behavior-initiating mechanisms if they strive to realistically simulate biological brains or out-compete other agents.