Kappel, Markus

Kretzberg, Jutta

Pirschel, Friederice

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Markus Kappel

Friederice Pirschel

Jutta Kretzberg

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Stimulus reconstruction based on postsynaptic potentials of leech interneurons

Kretzberg Jutta

Pirschel Friederice

Kappel Markus

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BMC Neuroscience

POSTER PRESENTATION Open Access
Stimulus reconstruction based on postsynaptic
potentials of leech interneurons
Markus Kappel, Friederice Pirschel, Jutta Kretzberg*
From Twentieth Annual Computational Neuroscience Meeting: CNS*2011
Stockholm, Sweden. 23-28 July 2011
Most studies on the neuronal encoding of sensory sti-
muli have been performed based on spike responses.
The classically considered neuronal response features
like spike count, spike timing or ISIs rely on the all-or-
nothing characteristic of spike responses. However, little
is known about stimulus encoding on the level of inte-
grated postsynaptic responses. In particular, no standard
methods exist to analyze stimulus encoding with graded
potentials. Moreover, the huge amount of stimulus-inde-
pendent fluctuations present in intracellularly recorded
membrane potentials complicates the analysis of graded
responses.
In this study, we use interneurons of the medical leech
to analyze stimulus encoding based on graded mem-
brane potential fluctuations. The local bend network
controls the reflex behavior of the leech bending away
when the skin is touched lightly [1]. It consists of four
sensory P (‘pressure’) cells, approximately 20 interneur-
ons and four groups of motorneurons, all of which can
be identified individually. EPSPs induced by P cell spikes
can be recorded intracellularly from the soma of inter-
neurons, where spike amplitudes are small (<7mV) [2].
In a related study (see Pirschel & Kretzberg, this issue)
we investigated the encoding of tactile stimulus para-
meters by P cell spike responses. We found that the
intensity of pressure applied to the skin influences the
spike count as well as the length of the 1st interspike
interval (ISI) and both response parameters yielded simi-
lar stimulus reconstruction performances. In this sense,
we have analyzed the influence of presynaptic P cell
spike count and 1st ISI on postsynaptic interneuron
responses. Precisely timed P cell spikes were elicited in
intracellular double recordings in five cell pairs with
short pulses of current injection. We simulated tactile
skin stimulation with three pressure intensities (≥6 pre-
sentations each) by inducing previously determined typi-
cal P cell spike responses, differing in spike count and
ISI lengths. For comparison, we used protocols in which
only the spike count or only the 1st ISI of P cell spikes
were varied. Stimulus reconstruction based on inter-
neuron recordings was performed with a maximum like-
lihood approach, using the area under the EPSP, the
EPSP slope, or the EPSP maximum amplitude.
When using the EPSP area and an optimal time win-
dow of ~100-300ms for stimulus reconstruction, the
three tactile stimuli simulated by realistic P cell spike
patterns were reconstructed correctly in ~70% of the
trials (chance level 33.3%). Interestingly, P cell responses
differing only in their 1st ISI could be discriminated fas-
ter (optimal time window 90-155ms) and more reliably
(up to 90% correct). However, P cell responses differing
only in spike count required long time windows
(>350ms) and reached lower reconstruction performance
(~50% correct). Using the EPSP slope yielded similar
reconstruction performances and optimal time scales,
but turned out to be more vulnerable to noisy data. Esti-
mation based on maximum EPSP amplitude led to con-
siderably lower performances.
Conclusions
1. The area under the interneuron EPSP is a suitable
responses feature for stimulus reconstruction.
2. Interneuron EPSPs in the leech local bend network
depend more strongly on the 1st ISI than on the spike
count of presynaptic P cell responses.
Acknowledgements
Supported by “Professorinnenprogramm” of the German Federal Ministry of
Education and Research.
Published: 18 July 2011
* Correspondence: jutta.kretzberg@uni-oldenburg.de
Computational Neuroscience, Institute of Biology and Environmental
Sciences, University of Oldenburg, D-26111 Oldenburg, Germany
Kappel et al. BMC Neuroscience 2011, 12(Suppl 1):P179
http://www.biomedcentral.com/1471-2202/12/S1/P179
© 2011 Kappel et al; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
References
1. Kristan WB, Calabrese RL, Friesen WO: Neuronal control of leech behavior.
J Progress in Neurobiology 2005, 76:279-327.
2. Lockery SR, Kristan WB: Distributed Processing of Sensory Information in
the Leech. II. Identification of Interneurons Contributing to the Local
Bending Reflex. J Neurosci 1990, 10(6):1816-l829.
doi:10.1186/1471-2202-12-S1-P179
Cite this article as: Kappel et al.: Stimulus reconstruction based on
postsynaptic potentials of leech interneurons. BMC Neuroscience 2011 12
(Suppl 1):P179.
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Kappel et al. BMC Neuroscience 2011, 12(Suppl 1):P179
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Submit your next manuscript to BioMed Central and take full advantage of: • Convenient online submission • Thorough peer review • No space constraints or color ﬁgure charges • Immediate publication on acceptance

WB: Distributed Processing of Sensory Information in the Leech. II. Identification of Interneurons Contributing to the Local Bending Reflex.

WO: Neuronal control of leech behavior.

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Stimulus reconstruction based on postsynaptic potentials of leech interneurons

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