Burst Waveform Research Articles

Spontaneous bursting and non-bursting activity in morphologically identified neurons of the rat dorsolateral septal nucleus, in vitro

Membrane potential-dependent changes in the repetitive firing properties of morphologically identified rat dorsolateral septal nucleus neurons were investigated in a submerged slice preparation using intracellular recording techniques and lithium acetate-Lucifer Yellow-filled microelectrodes. The results indicate that the majority of dorsolateral septal nucleus neurons are capable of burst firing and suggest, moreover, the existence of neuronal subtypes with distinct differences in spike waveform and the pattern of spontaneous activity. In the largest proportion of neurons, single spike activity predominated at membrane potentials near rest while burst-like discharges prevailed at more hyperpolarized membrane potentials. Less frequently observed were neurons exhibiting different burst waveforms at various membrane potentials. In a few neurons, hyperpolarization slowed neuronal firing but did not elicit burst-like discharges. Characteristics such as the presence of burst or single spike discharges, spike afterpotentials, and the membrane potential dependence of repetitive firing patterns did not appear to be closely associated with membrane time constant, membrane resistance, or resting membrane potential. A detailed examination of the somatodendritic and axonal morphology of the Lucifer Yellow-filled cells revealed that these electrophysiologically identified neurons in the dorsolateral septal nucleus are morphologically heterogeneous. However, there did not appear to be any correlation between a particular somatodendritic morphology and the expression of a distinct spontaneous firing pattern. The present findings demonstrate that neurons in the rat dorsolateral septal nucleus are morphologically diverse and capable of intrinsically generating rhythmic neuronal activity. Similar patterns of rhythmic neuronal firing in vivo may provide a substrate for the integration of afferent neuronal activity and have a central role in intraseptal circuitry necessary for generation of hippocampal theta rhythm.

Role of extracellular space in hyperosmotic suppression of potassium-induced electrographic seizures.

1. Focal electrographic seizures arose in the CA1 region of rat hippocampal slices bathed in elevated (8.5 mM) external potassium [( K+]o). High [K+]o also induced spontaneous interictal bursts that originated in area CA3 and propagated to CA1. To examine the contribution to electrographic seizure initiation of excitatory mechanisms that are influenced by extracellular volume, we studied the effect of hyperosmotic expansion of interstitial volume on seizure occurrence, interictal bursts, and excitatory synaptic transmission. The tissue electrical resistance was also measured leading up to and during seizures. 2. Media made 5-30 mosmol/kg hyperosmotic by addition of agents restricted to the extracellular space (mannitol, sucrose, raffinose, L-glucose, dextran) rapidly and reversibly abolished [K+]o-induced spontaneous CA1 seizures in 86% of slices tested. However, similar increases in osmolality effected by agents that access the intracellular compartment (D-glucose, glycerol) did not influence electrographic seizure occurrence. Hyperosmotic changes with plasma membrane impermeable compounds, but not permeable compounds, produced significant concentration-dependent decreases (1-10%) in the electrical resistance of CA1 stratum pyramidale. Because tissue resistance is proportional to extracellular volume, these results suggest that hyperosmotic suppression of electrographic seizures is associated with expansion of the extracellular space in hippocampal slices. 3. Measurement of electrical resistance of the CA1 stratum pyramidale during spreading depression and electrographic seizure revealed an increase in tissue resistance to 122% and 108% of control, respectively. Furthermore, a slight (approximately 2%) but significant increase in electrical resistance gradually occurred over the 20 s immediately preceding seizure generation. The observed increase in tissue resistance suggests extracellular space is decreased during these events. 4. Hyperosmolality did not alter CA3 interictal burst frequency. However, burst intensity, estimated from the total length of the burst waveform, was significantly reduced in both the CA3 (83% control) and CA1 region (67% control) when osmotic changes were imposed by plasma membrane impermeant compounds. Additionally, media made hypoosmotic by removal of 7.5 mM NaCl reversibly increased burst intensity. 5. High [K+]o potentiated excitatory synaptic transmission and excitatory postsynaptic potential (EPSP) spike coupling.(ABSTRACT TRUNCATED AT 400 WORDS)

Ambiguity Functions for Quadratic Phase-Coded Pulse Trains

The matched filter ambiguity function is presented for a burst waveform composed of repeated subbursts, each one of which consists of N pulses in which the phase is varied quadratically from pulse to pulse. The resulting ambiguity function exhibits small residual ambiguities along the delay axis separated by the reciprocal of the pulse repetition frequency (PRF). A cross-ambiguity function is derived which reduces these ambiguities to zero amplitude. A third cross-ambiguity function is presented for a receiver matched to a generalized Hamming weighted repeated quadratic burst. The location in the delay/Doppler plane of the waveform ambiguities for these waveforms is compared with that of an uncoded pulse burst.

A study of a class of detection waveforms having nearly ideal range—Doppler ambiguity properties

A special class of permutation matrices is considered. It is shown that these matrices may be beneficially used to determine the frequency-time pattern of a uniform pulse train. Proper choice of burst waveform parameters is shown to result in a detection wave-form having range and Doppler resolution properties consistent with the overall signal duration and bandwidth. The range-Doppler sidelobe peaks are well-controlled so that the ideal thumbtack ambiguity function behavior is closely approximated by the synthesis procedure presented.

Responses of primary auditory fibers to brief tone bursts.

Responses of primary auditory fibers to short triangularly modulated bursts of tone were obtained in the anesthetized cat. Based on discharge rate alone, the characteristics of the "response areas" obtained with these tone bursts were found to depend on the best frequency of the fiber. For a fiber with low best frequency (below 1 kHz), tones of greater than 10-ms duration had to be presented in order for the frequency resolution of the neuron to be as good as it was for long tones. For fibers with high best frequencies (above 10 kHz), tones of 2 or even 1 ms caused responses that were nearly as frequency selective as those obtained with long tones. A linear minimum-phase model based on the steady-state frequency selectivity of the fibers has been developed and shows generally comparable responses, but with some interesting exceptions. Synchronization of discharges to the waveform of the low-frequency tone bursts was measured and also shown to be generally compatible with the minimum-phase model. Trapezoidally modulated tone bursts were also used.

Amorphous threshold switch response to pulse burst waveforms

The switching response of thin-film amorphous chalcogenide threshold switches to pulse bursts of sine waves and square waves is reported. For the waveforms and devices investigated, preswitching behavior as evidenced by the delay time is a function of the rms voltage applied to the device. Switching voltages were slightly greater than the minimum required for switching.

Ambiguity Removal When Using Burst Waveforms. Part II: Nonlinear Processing

An effective technique for removing range ambiguities (detections at ranges other than the true range of the object) arising when using a burst waveform is to transmit two bursts with different pulse repetition frequencies nearly simultaneously and then to process their outputs nonlinearly. This correspondence introduces two nonlinear processors which combine coincidence detection with either noncoherent multiplication or integration. It is shown that the combined false alarm and ambiguity removal performance of these nonlinear processors is superior to the performance of coincidence detection, noncoherent multiplication, or noncoherent integration when used separately.

Algorithms for Multitarget Ambiguity Removal after Coincidence Detection

A first cut at the difficult problem of the identification and removal of ambiguous responses to radar burst waveforms is presented. Assuming that two bursts are used, algorithms for multitarget ambiguity removal after coincidence detection are presented and illustrated by examples. The results may have significant application in ballistic missile defense surveillance radars.

Ambiguity Removal When Using Burst Waveforms. Part I: Coincidence Detection

The uniformly spaced burst waveform provides excellent clutter rejection in cases where the clutter and targets are separated in velocity. However, it has the major disadvantage that an object at one range (at or near the search velocity) will give returns up and down range from the search range. If a simple threshold detection scheme is used which decides that an object is present at a location when the return at the corresponding time crosses a threshold, then a single object will give rise to many detections. (We shall call the detections at the ranges other than the true range of the object ambiguous detections, or ambiguities.) There are two classes of techniques to remove these ambiguities: those operating with a single transmission and those requiring additional transmissions. This correspondence considers the coincidence detection procedure which requires the transmission of two bursts with different pulse spacings. The detection and ambiguity removal performance of this algorithm is considered in detail for the case of scintillating targets.

An Algorithm for Designing Burst Waveforms with Quantized Transmitter Weights

An algorithm is described which finds optimum transmitter and receiver weights to maximize clutter suppression in a predetermined clutter region when using burst waveforms. It is assumed that the transmitter weights can only take on values from a finite set. This optimization problem is solved using a branch and bound algorithm. An example is given which shows the improvement in clutter suppression when this new design procedure is used as compared to a simpler nonoptimal procedure.

Effect of Radar Amplitude and Phase Weighting Errors on Clutter Rejection by Burst Waveforms

This correspondence derives simple expressions for the ambiguity function X and the Q function of uniformly spaced burst waveforms that are subject to independent random errors in the transmitter and receiver pulse phase and amplitude weightings. The expressions are similar to those in [1], but have been put in more simplified form, and are valid for more general sources of error.

Optimum Burst Waveforms for Detection of Targets in Uniform Range-Extended Clutter

Optimum Burst Waveforms for Detection of Targets in Uniform Range-Extended Clutter

An Application of Nonlinear Programming to Mismatched Filters

A burst waveform is a finite sequence of pulses with a staggered PRF. It is used as a high-resolution radar waveform. The ambiguity function of a burst waveform has a good peak-to-sidelobe ratio along the range axis. But, along the Doppler axis, its peak-to-sidelobe ratio is not nearly as good. A mismatched receiving filter is the logical way to increase the peak-to-sidelobe ratio of the ambiguity function along the Doppler axis. Taylor weighting only suppresses the Doppler sidelobes that are close to the main peak. In this paper, we derive, by the techniques of nonlinear programming, an iterative method for calculating a mismatched filter that is optimum in the following sense. Let an interval <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</tex> of the Doppler axis be specified, as well as a desired peak-to-sidelobe ratio W. Then our method will calculate the mismatched filter with optimum signal-to-noise ratio that reduces the Doppler sidelobes to the specified level over the specified interval, if such a filter exists. If such a filter does not exist, then the calculated filter will still tend to suppress the sidelobes over the specified interval of the Doppler axis.