Abstract
The present manuscript aims at identifying patterns of electrical activity recorded from neurons of the leech nervous system, characterizing specific behaviors. When leeches are at rest, the electrical activity of neurons and motoneurons is poorly correlated. When leeches move their head and/or tail, in contrast, action potential (AP) firing becomes highly correlated. When the head or tail suckers detach, specific patterns of electrical activity are detected. During elongation and contraction the electrical activity of motoneurons in the Medial Anterior and Dorsal Posterior nerves increase, respectively, and several motoneurons are activated both during elongation and contraction. During crawling, swimming, and pseudo-swimming patterns of electrical activity are better described by the dendrograms of cross-correlations of motoneurons pairs. Dendrograms obtained from different animals exhibiting the same behavior are similar and by averaging these dendrograms we obtained a template underlying a given behavior. By using this template, the corresponding behavior is reliably identified from the recorded electrical activity. The analysis of dendrograms during different leech behavior reveals the fine orchestration of motoneurons firing specific to each stereotyped behavior. Therefore, dendrograms capture the subtle changes in the correlation pattern of neuronal networks when they become involved in different tasks or functions.
Highlights
A major aim of Systems Neuroscience is the identification of patterns of electrical activity associated to sensory perceptions and underlying specific behaviors (Muller and Nicholls, 1974; Baader and Kristan, 1995; Reynolds et al, 1998; Nicholls, 2001; Kristan et al, 2005)
The nervous system of most vertebrates is composed by millions and often billions of neurons and present experimental tools allow the recording of the electrical activity of a very small—and often negligible—fraction of these neurons and it is very difficult to relate patterns of electrical activity to specific behaviors
Semi-intact leeches can be studied for several hours while their electrical activity is recorded and their behavior monitored www.frontiersin.org allowing the identification and characterization of patterns of electrical activity underlying specific behaviors (Figure 1)
Summary
A major aim of Systems Neuroscience is the identification of patterns of electrical activity associated to sensory perceptions and underlying specific behaviors (Muller and Nicholls, 1974; Baader and Kristan, 1995; Reynolds et al, 1998; Nicholls, 2001; Kristan et al, 2005). The spontaneous behavior and the reaction to stimuli are mediated by 21 pairs of excitatory motoneurons and 7 pairs of inhibitory motoneurons, innervating the four different muscular synergies referred to as longitudinal, oblique, dorsoventral, and circular muscular fibers (Mason and Kristan, 1982; Norris and Calabrese, 1987; Lockery and Kristan, 1990a,b) These motoneurons have been extensively investigated using force and length transducers, imaging of muscle contractions and other electrophysiology tools (Stuart, 1970; Ort et al, 1974; Friesen et al, 1978; Kristan, 1982; Mason and Kristan, 1982; Norris and Calabrese, 1987; Zoccolan et al, 2001, 2002; Zoccolan and Torre, 2002; Garcia-Perez et al, 2004)
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