25th annual computational neuroscience meeting: CNS-2016

The same neuron may play different functional roles in the neural circuits to which it belongs. For example, neurons in the Tritonia pedal ganglia may participate in variable phases of the swim motor rhythms [1]. While such neuronal functional variability is likely to play a major role the delivery of the functionality of neural systems, it is difficult to study it in most nervous systems. We work on the pyloric rhythm network of the crustacean stomatogastric ganglion (STG) [2]. Typically network models of the STG treat neurons of the same functional type as a single model neuron (e.g. PD neurons), assuming the same conductance parameters for these neurons and implying their synchronous firing [3, 4]. However, simultaneous recording of PD neurons shows differences between the timings of spikes of these neurons. This may indicate functional variability of these neurons. Here we modelled separately the two PD neurons of the STG in a multi-neuron model of the pyloric network. Our neuron models comply with known correlations between conductance parameters of ionic currents. Our results reproduce the experimental finding of increasing spike time distance between spikes originating from the two model PD neurons during their synchronised burst phase. The PD neuron with the larger calcium conductance generates its spikes before the other PD neuron. Larger potassium conductance values in the follower neuron imply longer delays between spikes, see Fig. 17.Neuromodulators change the conductance parameters of neurons and maintain the ratios of these parameters [5]. Our results show that such changes may shift the individual contribution of two PD neurons to the PD-phase of the pyloric rhythm altering their functionality within this rhythm. Our work paves the way towards an accessible experimental and computational framework for the analysis of the mechanisms and impact of functional variability of neurons within the neural circuits to which they belong

Information Circular 22. Analytical Results of the Public Geologic Sample Program, 1983-1985 Biennium

In 1983 the Minnesota Geological Survey, in conjunction with the Minnesota Department of Natural Resources, Division of Minerals, began a geologic sample program whereby the general public was encouraged to submit samples of geologic material for identification and possible analysis. The program was roughly patterned after a similar program in Finland. The Finnish program has resulted in a heightened public interest in the mineral potential of that country and has resulted in the discovery of several ore deposits. It was for those reasons, as well as the potential increase in geologic knowledge that could result, that a similar program was initiated in Minnesota. As originally conceived, the geologic sample program was to focus on samples submitted to the Minnesota Geological Survey by the general public. As part of its public service function, the Survey was to identify and classify rock or mineral samples that were collected in the state. If any of the samples were thought to have potential scientific or economic interest, they were to be submitted for chemical analyses or other appropriate tests. A copy of a brochure that was prepared to advertise the program is shown in Figure 1, and the sample submittal form that sets forth the operating conditions for the program is shown in Figure 2. The brochure and other publicity about the program led to requests for 238 submittal forms and to approximately 500 walk-in and telephone requests for additional information. Unfortunately, of the more than 700 inquiries, only 9 samples were ultimately judged suitable for additional chemical analysis (Table 1). The "suitability" rate of only slightly more than 1 percent was due to a number of factors. Many people only became aware of the program very late in the biennium. Other people who had samples of scientific or economic interest were unwilling to submit those samples to the Geological Survey for several reasons, including (a) the expense of mailing samples, (b) an unwillingness to part with a "prized" specimen, or (c) a lack of knowledge about mineral rights (i.e., a fear of jeopardizing their rights by revealing the location of a sample). However the great majority of samples were submitted by individuals who simply wanted them identified without concern as to possible scientific or economic value. Because of the sluggish public response, the program was modified in early 1985 to include samples of scientific or economic interest that were submitted by personnel of the Minnesota Department of Natural Resources, Division of Minerals, or the Minnesota Geological Survey. This programmatic change led to the additional analysis of 304 samples from various components of the Early Proterozoic Animikie basin on the Mesabi and Cuyuna ranges and in east-central Minnesota (Tables 2, 3, 4, and 7) and from various poorly known rock units in southwestern (Tables 5 and 8) and southeastern Minnesota (Tables 6 and 9)