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The spike generation zone of the ampullary electroreceptor (1995)

Bruner, L. J. ; Harvey, J. R.

Springer

Biological cybernetics 72 (1995), S. 371-378

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ISSN: 1432-0770

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Computer Science , Physics

Notes: Abstract Sensory input to the central nervous system begins with a transduction step, specialized to the sensory modality involved, resulting in the production of postsynaptic electrical input to the outermost branches of a dendritic tree. Spatiotemporal summation of this ‘slow’ input as it converges upon the axon then initiates the production of or modulates the rate of ongoing production of ‘fast’ neural spikes destined for the central nervous system. We present a novel circuit design consisting of an operational amplifier, a tunnel diode and linear passive components, intended to model the spike generation zone at which the transformation of neural input from slow to fast format takes place. Our circuit is shown to be a relaxation oscillator of the van der Pol type. Simulated postsynaptic current modulates the frequency of spike production by the relaxation oscillator model, producing a stimulus-response characteristic which can be compared with those observed in vivo. Stimulus-response data for our model match data available in the literature for the ampullary electroreceptor of elasmobranch fish.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00201412

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2

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Neural spike generator entrainment by regularly spaced synaptic input (1997)

Harvey, J. R. ; Bruner, L. J.

Springer

Biological cybernetics 76 (1997), S. 409-418

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ISSN: 1432-0770

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Computer Science , Physics

Notes: Abstract. It has been known for 30 years that the output of a repetitively firing neuron or pacemaker can be synchronized (locked) to regularly spaced inhibitory or excitatory postsynaptic input potentials. Conditions for stable locking have been determined mathematically, demonstrated in computer simulation, and locking has been observed in vivo. We have developed a neural spike generator circuit model which exhibits stable locking to externally derived simulated inhibitory or excitatory post-synaptic inputs. Conditions for stable 1 : 1 lock, in which pacemaker output frequency matches that of the periodic input, are derived. These take the form of expressions for stable delay and convergence factor which incorporate known or measurable parameters of the circuit model. The expressions have been evaluated and shown to compare satisfactorily with experimental observations of locking by our circuit model.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004220050354

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The spike generation zone of the ampullary electroreceptor (1995)

Harvey, J. R. ; Bruner, L. J.

Springer

Biological cybernetics 72 (1995), S. 379-387

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ISSN: 1432-0770

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Computer Science , Physics

Notes: Abstract. Our preceding paper presented a relaxation oscillator model generally applicable to the description of the spike generation zone of an afferent nerve fiber. This model was shown to reproduce the measured stimulus-response characteristics of the elasmobranch ampullary electroreceptor. In this paper, our optimized model is shown to resolve input stimulus currents or current shifts as small as 50 fA. The fractional spike generator frequency shift produced by injection of this minimum resolvable current is Δ f / f≈2×10-3. Arguments based upon known properties of both glutamatergic postsynaptic membrane channels and the electroreceptor organ suggest that this resolvability substantially exceeds that required to account for the known sensitivity of elasmobranch fish to marine electric fields. Our estimates of synaptic input current noise indicate that it will limit the minimum resolvable fractional change of synaptic input current to the range 10-1−10-2 and will thereby limit the minimum resolvable in vivo spike generator fractional frequency shift to the same range. For our optimized model, increase of the minimum resolvable fractional shift of spike generator frequency into this range can be accomplished by injection of ‘white’ stimulus current noise of ≈1 pA rms, over a bandwidth of 4–200 Hz. These results lead to the conclusion that synaptic input current noise, rather than inherent spike generator stability, limits electroreceptive sensitivity in vivo. This noise limit is also consistent with the Weber-Fechner criterion derived from psychophysical studies, which places the minimum resolvable fractional change of input stimulus in this same range. We suggest that synaptic current noise provides the physiological basis for the Weber-Fechner criterion. The model studies of this and the preceding paper indicate that the remarkable electroreceptive sensitivity exhibited by marine elasmobranches can be accounted for within the framework of well-known physical principles, with no requirement of ad hoc assumptions relating to the structure or function of the electroreceptor organ.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004220050140

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4

Electronic Resource

The spike generation zone of the ampullary electroreceptor (1995)

Harvey, J. R. ; Bruner, L. J.

Springer

Biological cybernetics 72 (1995), S. 379-387

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Details

ISSN: 1432-0770

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Computer Science , Physics

Notes: Abstract Our preceding paper presented a relaxation oscillator model generally applicable to the description of the spike generation zone of an afferent nerve fiber. This model was shown to reproduce the measured stimulus-response characteristics of the elasmobranch ampullary electroreceptor. In this paper, our optimized model is shown to resolve input stimulus currents or current shifts as small as 50 fA. The fractional spike generator frequency shift produced by injection of this minimum resolvable current is Δf/f≈2×10−3. Arguments based upon known properties of both glutamatergic postsynaptic membrane channels and the electroreceptor organ suggest that this resolvability substantially exceeds that required to account for the known sensitivity of elasmobranch fish to marine electric fields. Our estimates of synaptic input current noise indicate that it will limit the minimum resolvable fractional change of synaptic input current to the range 10−1–10−2 and will thereby limit the minimum resolvable in vivo spike generator fractional frequency shift to the same range. For our optimized model, increase of the minimum resolvable fractional shift of spike generator frequency into this range can be accomplished by injection of ‘white’ stimulus current noise of ≈ 1 pA rms, over a bandwidth of 4–200 Hz. These results lead to the conclusion that synaptic input current noise, rather than inherent spike generator stability, limits electroreceptive sensitivity in vivo. This noise limit is also consistent with the Weber-Fechner criterion derived from psychophysical studies, which places the minimum resolvable fractional change of input stimulus in this same range. We suggest that synaptic current noise provides the physiological basis for the Weber-Fechner criterion. The model studies of this and the preceding paper indicate that the remarkable electroreceptive sensitivity exhibited by marine elasmobranches can be accounted for within the framework of well-known physical principles, with no requirement of ad hoc assumptions relating to the structure or function of the electroreceptor organ.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00201413

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5

Electronic Resource

The spike generation zone of the ampullary electroreceptor (1995)

Bruner, L. J. ; Harvey, J. R.

Springer

Biological cybernetics 72 (1995), S. 371-378

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Details

ISSN: 1432-0770

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Computer Science , Physics

Notes: Abstract. Sensory input to the central nervous system begins with a transduction step, specialized to the sensory modality involved, resulting in the production of postsynaptic electrical input to the outermost branches of a dendritic tree. Spatiotemporal summation of this ‘slow’ input as it converges upon the axon then initiates the production of or modulates the rate of ongoing production of ‘fast’ neural spikes destined for the central nervous system. We present a novel circuit design consisting of an operational amplifier, a tunnel diode and linear passive components, intended to model the spike generation zone at which the transformation of neural input from slow to fast format takes place. Our circuit is shown to be a relaxation oscillator of the van der Pol type. Simulated postsynaptic current modulates the frequency of spike production by the relaxation oscillator model, producing a stimulus-response characteristic which can be compared with those observed in vivo. Stimulus-response data for our model match data available in the literature for the ampullary electroreceptor of elasmobranch fish.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004220050139

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6

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Synchronization of pacemaker cell firing by weak ELF fields: Simulation by a circuit model (1998)

Bruner, L. J. ; Harvey, J. R.

New York, NY [u.a.] : Wiley-Blackwell

Bioelectromagnetics 19 (1998), S. 92-97

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ISSN: 0197-8462

Keywords: action potentials ; excitable membrane ; postsynaptic potentials ; electronic circuit ; stimulation ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Physics

Notes: Entrainment of output action potentials from repetitively firing pacemaker cells, brought about by regularly spaced excitatory or inhibitory postsynaptic inputs, is a well-known phenomenon. Synchronization of neural firing patterns by extremely low frequency (ELF) external electric fields has also been observed. Whereas current densities of ≈10 A-m-2 are required for direct excitation of otherwise quiescent neural tissue, much lower peak current densities (≈10-2 A-m2) have been reported to entrain spontaneously firing molluscan pacemaker cells. We have developed a neural spike generator circuit model that simulates repetitive spike generation by a space clamped patch (area ≈ 10-7 m2) of excitable membrane subjected to depolarizing current. Picoampere (pA) range variation of DC depolarizing current causes a corresponding smooth variation of neural spike frequency, producing a physiologically realistic stimulus-response (S-R) characteristic. When lower pA range 60 Hz AC current is superposed upon the DC depolarizing current, smooth variation of the S-R characteristic is distorted by subharmonic locking of the spike generator at 30, 20, 15, 12, 10 Hz, and higher order subharmonic frequencies. Although the additional superposition of a physiologically realistic level of “white” current noise, covering the bandwidth 4-200 Hz, suffices to obscure higher order subharmonic locking, locking at 30, 20, and 15 Hz is still clearly evident in the presence of noise. Subharmonic locking is observed at a root mean square AC simulated tissue current density of ≈10-5 A-m-2. Bioelectromagnetics 19:92-97, 1998. © 1998 Wiley-Liss, Inc.

Additional Material: 4 Ill.

Type of Medium: Electronic Resource

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