Network adaptation improves temporal representation of naturalistic stimuli in drosophila eye: II Mechanisms

Retinal networks must adapt constantly to best present the ever changing visual world to the brain. Here we test the hypothesis that adaptation is a result of different mechanisms at several synaptic connections within the network. In a companion paper (Part I), we showed that adaptation in the photoreceptors (R1-R6) and large monopolar cells (LMC) of the Drosophila eye improves sensitivity to under-represented signals in seconds by enhancing both the amplitude and frequency distribution of LMCs' voltage responses to repeated naturalistic contrast series. In this paper, we show that such adaptation needs both the light-mediated conductance and feedback-mediated synaptic conductance. A faulty feedforward pathway in histamine receptor mutant flies speeds up the LMC output, mimicking extreme light adaptation. A faulty feedback pathway from L2 LMCs to photoreceptors slows down the LMC output, mimicking dark adaptation. These results underline the importance of network adaptation for efficient coding, and as a mechanism for selectively regulating the size and speed of signals in neurons. We suggest that concert action of many different mechanisms and neural connections are responsible for adaptation to visual stimuli. Further, our results demonstrate the need for detailed circuit reconstructions like that of the Drosophila lamina, to understand how networks process information

High concentrations of amorphous, biogenic Si (BSi) in the sediment of a small high-latitude lake: implications for biogeochemical Si cycling and for the use of BSi as a paleoproxy

The concentration of biogenic silica (BSi) in soils and sediments may be studied for several purposes, most notably either as a paleo-environmental proxy or to clarify the transport of weathering-derived Si within the biogeosphere. With this in mind, we explored the reasons behind the very high BSi concentration (average 250 mg Si g-1 dry mass) in the sediment of a small, highlatitude lake in Finnish Lapland, Lake Kuutsja¨rvi, using bulk BSi and stable Si isotope analysis of major Si pools in the lake and its drainage area. The high BSi content of the sediment was relatively stable over the past few hundred years and recent changes in the food web of the lake were not clearly reflected in the data. The origin of the sedimentary BSi was not solely autochthonous diatom production: extraneous sources accounted for possibly as much as 54–88 % (isotope analysis). A main reason for the high BSi content appeared to be the transport of older deposits of diatom material from the drainage area into the current lake basin, although other factors such as good preservation conditions may have contributed. Although our results indicate that small high-latitude lakes may be hot-spots in the burial of BSi, more information is needed on the processes that affect the translocation of BSi from the drainage area to the aquatic system. Caution is advisable when past lake conditions are inferred from sedimentary BSi only

Applications of paleoenvironmental techniques in estuarine studies

The aim of this edited volume is to introduce the scientific community to paleoenvironmental studies of estuaries, to highlight the types of information that can be obtained from such studies, and to promote the use of paleoenvironmental studies in estuarine management. Readers will learn about the the application of different paleoecological approaches used in estuaries that develop our understanding of their response to natural and human influences. Particular attention is given to the essential steps required for undertaking a paleoecological study, in particular with regard to site selection, core extraction and chronological techniques, followed by the range of indicators that can be used. A series of case studies are discussed in the book to demonstrate how paleoecological studies can be used to address key questions, and to sustainably manage these important coastal environments in the future. This book will appeal to professional scientists interested in estuarine studies and/or paleoenvironmental research, as well as estuarine managers who are interested in the incorporation of paleoenvironmental research into their management programs