Soma-Axon Coupling Configurations That Enhance Neuronal Coincidence Detection

Coincidence detector neurons transmit timing information by responding preferentially to concurrent synaptic inputs. Principal cells of the medial superior olive (MSO) in the mammalian auditory brainstem are superb coincidence detectors. They encode sound source location with high temporal precision, distinguishing submillisecond timing differences among inputs. We investigate computationally how dynamic coupling between the input region (soma and dendrite) and the spike-generating output region (axon and axon initial segment) can enhance coincidence detection in MSO neurons. To do this, we formulate a two-compartment neuron model and characterize extensively coincidence detection sensitivity throughout a parameter space of coupling configurations. We focus on the interaction between coupling configuration and two currents that provide dynamic, voltage-gated, negative feedback in subthreshold voltage range: sodium current with rapid inactivation and low-threshold potassium current, IKLT. These currents reduce synaptic summation and can prevent spike generation unless inputs arrive with near simultaneity. We show that strong soma-to-axon coupling promotes the negative feedback effects of sodium inactivation and is, therefore, advantageous for coincidence detection. Furthermore, the feedforward combination of strong soma-to-axon coupling and weak axon-to-soma coupling enables spikes to be generated efficiently (few sodium channels needed) and with rapid recovery that enhances high-frequency coincidence detection. These observations detail the functional benefit of the strongly feedforward configuration that has been observed in physiological studies of MSO neurons. We find that IKLT further enhances coincidence detection sensitivity, but with effects that depend on coupling configuration. For instance, in models with weak soma-to-axon and weak axon-to-soma coupling, IKLT in the axon enhances coincidence detection more effectively than IKLT in the soma. By using a minimal model of soma-to-axon coupling, we connect structure, dynamics, and computation. Although we consider the particular case of MSO coincidence detectors, our method for creating and exploring a parameter space of two-compartment models can be applied to other neurons

Electrosensory Frequency and Intensity Discrimination in the Wave-Type Electric Fish Eigenmannia

Eigenmannia's frequency and intensity discrimination thresholds were determined for a range of seven frequencies (50-1700Hz), centered on a fish's individual discharge frequency, using a conditioned go/no-go paradigm. The threshold criterion was '50% correct choices' (of the rewarded stimulus, S+, over the unrewarded stimulus, S—); this was validated by testing for statistically significantly shorter response latencies for the S+ compared with the S— stimulus. The stimuli consisted of sine wave bursts presented for up to 20 s, repeated at 2 s"1 (rise and fall times of an individual burst, 50 ms; holding time, 250 ms; silence, 150ms). When testing for frequency discrimination, the sine wave bursts alternated in frequency (A/); for intensity discrimination, every other sine wave burst was of increased intensity (A/). The reference stimulus intensity was 30 dB with reference to a fish's individual absolute threshold for a continuous sine wave at that frequency, previously determined using a conditioned go response. Sensory discrimination was best close to a fish's individual discharge frequency. At 30 dB sensation level, fish discriminated frequency differences as small as 0.52 Hz (0.60 and 0.79 Hz in two other individuals) and intensity differences as small as 0.56dB (1 dB in two other fish). At stimulus frequencies different from a fish's discharge frequency, Eigenmannia's frequency discrimination declined at lower frequencies at a rate of up to 1 Hz octave"1, and at higher frequencies at a rate of up to 3 Hz octave"1. For Eigenmannia's intensity discrimination a similar loss was observed: at frequencies lower than a fish's discharge frequency, intensity discrimination thresholds rose at a rate of less than 1 dB octave" *, while the rate was below 2 dB octave"1 for higher frequencies. Compared with other acoustico-lateral senses in lower vertebrates, Eigenmannia's electrosensory frequency and intensity discrimination is unusually high, in the range of that known for audition in the most sensitive higher vertebrates with a cochlea (for example, human). This emphasizes Eigenmannia's specialized 'active' electrosensory system, which detects the presence of a stimulus field as the modulation of a fish's own 'carrier' signal in amplitude and phase (beat analysis), as opposed to 'passive' sensory systems, which must deal with unpredictable signals from the environment as they occur

Space Shuttle program communication and tracking systems interface analysis

The Space Shuttle Program Communications and Tracking Systems Interface Analysis began April 18, 1983. During this time, the shuttle communication and tracking systems began flight testing. Two areas of analysis documented were a result of observations made during flight tests. These analyses involved the Ku-band communication system. First, there was a detailed analysis of the interface between the solar max data format and the Ku-band communication system including the TDRSS ground station. The second analysis involving the Ku-band communication system was an analysis of the frequency lock loop of the Gunn oscillator used to generate the transmit frequency. The stability of the frequency lock loop was investigated and changes to the design were reviewed to alleviate the potential loss of data due the loop losing lock and entering the reacquisition mode. Other areas of investigation were the S-band antenna analysis and RF coverage analysis

Intelligent redundant actuation system requirements and preliminary system design

Several redundant actuation system configurations were designed and demonstrated to satisfy the stringent operational requirements of advanced flight control systems. However, this has been accomplished largely through brute force hardware redundancy, resulting in significantly increased computational requirements on the flight control computers which perform the failure analysis and reconfiguration management. Modern technology now provides powerful, low-cost microprocessors which are effective in performing failure isolation and configuration management at the local actuator level. One such concept, called an Intelligent Redundant Actuation System (IRAS), significantly reduces the flight control computer requirements and performs the local tasks more comprehensively than previously feasible. The requirements and preliminary design of an experimental laboratory system capable of demonstrating the concept and sufficiently flexible to explore a variety of configurations are discussed

Energy integration describes sound-intensity coding in an insect auditory system

We investigate the transduction of sound stimuli into neural responses and focus on locust auditory receptor cells. As in other mechanosensory model systems, these neurons integrate acoustic inputs over a fairly broad frequency range. To test three alternative hypotheses about the nature of this spectral integration (amplitude, energy, pressure), we perform intracellular recordings while stimulating with superpositions of pure tones. On the basis of online data analysis and automatic feedback to the stimulus generator, we systematically explore regions in stimulus space that lead to the same level of neural activity. Focusing on such iso-firing-rate regions allows for a rigorous quantitative comparison of the electrophysiological data with predictions from the three hypotheses that is independent of nonlinearities induced by the spike dynamics. We find that the dependence of the firing rates of the receptors on the composition of the frequency spectrum can be well described by an energy-integrator model. This result holds at stimulus onset as well as for the steady-state response, including the case in which adaptation effects depend on the stimulus spectrum. Predictions of the model for the responses to bandpass-filtered noise stimuli are verified accurately. Together, our data suggest that the sound-intensity coding of the receptors can be understood as a three-step process, composed of a linear filter, a summation of the energy contributions in the frequency domain, and a firing-rate encoding of the resulting effective sound intensity. These findings set quantitative constraints for future biophysical models

A high-speed multi-protocol quantum key distribution transmitter based on a dual-drive modulator

We propose a novel source based on a dual-drive modulator that is adaptable and allows Alice to choose between various practical quantum key distribution (QKD) protocols depending on what receiver she is communicating with. Experimental results show that the proposed transmitter is suitable for implementation of the Bennett and Brassard 1984 (BB84), coherent one-way (COW) and differential phase shift (DPS) protocols with stable and low quantum bit error rate. This could become a useful component in network QKD, where multi-protocol capability is highly desirable.Comment: 15 pages, 7 figure