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Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Electrophysiological characterization of interlaminar entorhinal connections: an essential link for re-entrance in the hippocampal,entorhinal system

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2003
Fabian Kloosterman
Abstract The hippocampal formation communicates with the neocortex mainly through the adjacent entorhinal cortex. Neurons projecting to the hippocampal formation are found in the superficial layers of the entorhinal cortex and are largely segregated from the neurons receiving hippocampal output, which are located in deep entorhinal layers. We studied the communication between deep and superficial entorhinal layers in the anaesthetized rat using field potential recordings, current source density analysis and single unit measurements. We found that subiculum stimulation was able to excite entorhinal neurons in deep layers. This response was followed by current sinks in superficial layers. Both responses were subject to frequency dependent facilitation, but not depression. Selective blockade of deep layer responses also abolished subsequent superficial layer responses. This clearly demonstrates a functional deep-to-superficial layer communication in the entorhinal cortex, which can be triggered by hippocampal output. This pathway may provide a means by which processed hippocampal output is integrated or compared with new incoming information in superficial entorhinal layers, and it constitutes an important link in the process of re-entrance of activity in the hippocampal,entorhinal network, which may be important for consolidation of memories or retaining information for short periods. [source]

Enhancement of temporal and spatial synchronization of entorhinal gamma activity by phase reset

HIPPOCAMPUS, Issue 4 2002
Clayton T. Dickson
Abstract The synchronization of cortical gamma oscillatory activity (25,80 Hz) is thought to coordinate neuronal assemblies in the processing and storage of information. The mechanism by which independently oscillating and distantly located cortical zones become synchronized is presumed to involve activity in corticocortical connections, although evidence supporting this conjecture has only been indirect. In the present study, we show that activation of synaptic inputs within and to the medial entorhinal cortex (mEC) of the in vitro isolated guinea pig brain preparation resets the phase of ongoing gamma activity induced by muscarinic receptor agonism with carbachol (frequency: 24 ± 2 Hz at 32°C). Phase reset was associated with a transient enhancement of the synchronization of gamma activity recorded at distant (>1 mm) mEC sites, across which low coherence (>0.75) was observed before stimulation. This increase in synchronization, as measured by cross-correlation analysis, was restricted to a maximal period of 200 ms after either local mEC or CA1 afferent stimulation. The results provide direct evidence that synaptic activation can enhance the rhythmic synchronization of spatially remote, independently oscillating neuronal assemblies in the mEC through a mechanism of synaptically evoked phase reset. Dynamic functional grouping of oscillatory discharges across long distances in the mEC may underlie coding processes involved in the integration and storage of incoming information and thus may be important for the role of this region in memory processes. Hippocampus 2002;12:447,456. © 2002 Wiley-Liss, Inc. [source]

A Comparison of Exit and Voice Relationships Under Common Uncertainty

JOURNAL OF ECONOMICS & MANAGEMENT STRATEGY, Issue 4 2003
Herbert Dawid
We consider a repeated interaction between a manufacturing firm and a subcontractor. The relationship between the two parties is characterized (1) by moral hazard, and (2) by the fact that they do not have perfect knowledge about the base cost level of the project, which is carried out by a subcontractor (the parties only have identical a priori beliefs). We consider a two-period model where the players can update their estimate of the base cost level according to incoming information. Exit relationships, where the firm signs one-period contracts with different subcontractors, are compared with voice relationships, where both partners commit to a two-period interaction and (due to information sharing and face-to-face communication between the partners) additional information about the base cost level is generated. It is shown that in such a dynamic framework with common uncertainty the quality of the additional information plays a crucial role in determining the characteristics of the optimal relationship: voice-based strategies governed by long-term contracts are preferable if the precision of the additional information about the base cost level is high. If the precision of the additional signal is low, exit strategies with frequent changes of the subcontractors are optimal for the manufacturer. [source]

A General Empirical Law of Public Budgets: A Comparative Analysis

AMERICAN JOURNAL OF POLITICAL SCIENCE, Issue 4 2009
Bryan D. Jones
We examine regularities and differences in public budgeting in comparative perspective. Budgets quantify collective political decisions made in response to incoming information, the preferences of decision makers, and the institutions that structure how decisions are made. We first establish that the distribution of budget changes in many Western democracies follows a non-Gaussian distribution, the power function. This implies that budgets are highly incremental, yet occasionally are punctuated by large changes. This pattern holds regardless of the type of political system,parliamentary or presidential,and for level of government. By studying the power function's exponents we find systematic differences for budgetary increases versus decreases (the former are more punctuated) in most systems, and for levels of government (local governments are less punctuated). Finally, we show that differences among countries in the coefficients of the general budget law correspond to differences in formal institutional structures. While the general form of the law is probably dictated by the fundamental operations of human and organizational information processing, differences in the magnitudes of the law's basic parameters are country- and institution-specific. [source]