The Effect of Alkaloids on Fluorescence in Solutions

The quenching of fluorescence of different substances by a series of alkaloids has \u27 been studied. The alkaloids generally exert a quenching action on the fluorescence. In evaluating these effects, in certain cases it is necessary to take into consideration the absorptii. on of exciting light by the molecules of the quencher. The quenching effect of the anions of ailka loid salts should also be taken into account. By .mathematical corrections of experimental data for the absorption of the exciting light and the quenching by anions, the constants and semi-concentrations of quenching are obtained for the cation:ic part of the alkaloid. It may be assumed that the quenching effect of alkaloids involves an external static mechanism, i. e. the formation of molecular compounds between the quencher and the fluorescent substance

Dual coding with STDP in a spiking recurrent neural network model of the hippocampus.

The firing rate of single neurons in the mammalian hippocampus has been demonstrated to encode for a range of spatial and non-spatial stimuli. It has also been demonstrated that phase of firing, with respect to the theta oscillation that dominates the hippocampal EEG during stereotype learning behaviour, correlates with an animal's spatial location. These findings have led to the hypothesis that the hippocampus operates using a dual (rate and temporal) coding system. To investigate the phenomenon of dual coding in the hippocampus, we examine a spiking recurrent network model with theta coded neural dynamics and an STDP rule that mediates rate-coded Hebbian learning when pre- and post-synaptic firing is stochastic. We demonstrate that this plasticity rule can generate both symmetric and asymmetric connections between neurons that fire at concurrent or successive theta phase, respectively, and subsequently produce both pattern completion and sequence prediction from partial cues. This unifies previously disparate auto- and hetero-associative network models of hippocampal function and provides them with a firmer basis in modern neurobiology. Furthermore, the encoding and reactivation of activity in mutually exciting Hebbian cell assemblies demonstrated here is believed to represent a fundamental mechanism of cognitive processing in the brain