Conjunctive Processing of Locomotor Signals by the Ventral Tegmental Area Neuronal Population

The ventral tegmental area (VTA) plays an essential role in reward and motivation. How the dopamine (DA) and non-DA neurons in the VTA engage in motivation-based locomotor behaviors is not well understood. We recorded activity of putative DA and non-DA neurons simultaneously in the VTA of awake mice engaged in motivated voluntary movements such as wheel running. Our results revealed that VTA non-DA neurons exhibited significant rhythmic activity that was correlated with the animal's running rhythms. Activity of putative DA neurons also correlated with the movement behavior, but to a lesser degree. More importantly, putative DA neurons exhibited significant burst activation at both onset and offset of voluntary movements. These findings suggest that VTA DA and non-DA neurons conjunctively process locomotor-related motivational signals that are associated with movement initiation, maintenance and termination

Applications of weak beams in electron microscopy

The basic ideas and development of the weak beam method (Cockayne, Ray an Whelan, 1969) are described. Results obtained for the dislocation core structure in the diamond structure and in face-centred cubic metals are reviewed together with some recent observations obtained at high voltages. The main experimental difficulties of the weak beam method are stage stability for long exposures and loss of contrast because of the diffuse background. These problems are discussed and a perturbation theory for the more rapid computation of weak beam images is described. This theory can also be used for calculations of antiphase domain boundary images in ordered alloys.On décrit les bases et le développement de la méthode des faisceaux faibles (Cockayne, Ray et Whelan, 1969). On présente une revue des résultats obtenus pour la structure du cœur des dislocations dans la structure type diamant et dans les métaux cubiques à faces centrées, ainsi que quelques récentes observations faites à très haute tension. Les difficultés principales pour la méthode des faisceaux faibles proviennent de la stabilité de la platine pour des temps d'exposition longs, et de la perte de contraste due au bruit de fond produit par la diffusion. On discute de ces problèmes et on décrit une théorie des perturbations pour le calcul plus rapide des images en faisceau faible. Cette théorie peut également être utilisée pour les calculs des images de paroi de domaines d'antiphase dans les alliages ordonnés.Howie Archibald, Stobbs W. M., Gai Pratibha L. Applications of weak beams in electron microscopy. In: Bulletin de la Société française de Minéralogie et de Cristallographie, volume 95, 6, 1972. pp. 690-699

Weak beam under convergent beam illumination

The weak beam technique is now used widely for the determination of stacking fault energies, in particular for intermetallic alloys, and the accuracy of the approach is critically dependent upon the reliability of the relationship between the image and the actual position of the dissociated dislocations. Examining as a model case a dislocation dissociated into two Shockley partial dislocations in Cu at 100 kV for orientations ranging through the g(3g) weak beam condition, image simulations are used to explore the accuracy to which the true spacing between the partial dislocations can be determined from the spacing measured on the image as a function of the dislocation character, the foil thickness, the dislocation depth in the foil, the diffraction condition and the beam convergence. It appears that for image simulations and for the given conditions a beam convergence of about 5 mrad allows to greatly improve the accuracy, and that beam convergence must be taken into account quantitatively when deducing the true partial dislocation spacing as it is the principal parameter controlling the precision in this type of measurement. (C) 2000 Elsevier Science B.V. All rights reserved