Positive feedback loops sustain repeating bursts in neuronal circuits.

Area of Science:

• Neuroscience
• Animal Behavior
• Computational Biology

Background:

• Voluntary movements in animals are episodic, requiring sustained neuronal excitation.
• Existing models explain swim initiation in leeches but not prolonged swim episodes.
• Mechanisms sustaining neuronal excitation for extended movements remain largely unknown.

Purpose of the Study:

• Investigate mechanisms maintaining swimming activity in the medicinal leech.
• Identify the role of intersegmental interactions in sustained locomotion.
• Develop and validate a computational model of leech swimming.

Main Methods:

• Physiological experiments on medicinal leeches.
• Development of a computational model of neuronal circuits.
• Analysis of neuronal excitation, impulse adaptation, and nerve cord length effects.

Main Results:

• Intrasegmental mechanisms prolong excitation for only brief periods.
• Mutually excitatory intersegmental neuronal interactions drive sustained swimming.
• The model accurately replicated experimental findings on swim initiation, duration, and termination.

Conclusions:

• Sustained swimming in leeches relies on mutually excitatory intersegmental neuronal chains.
• Impulse adaptation in neurons is crucial for regulating swim bout duration.
• This study provides a framework for understanding sustained voluntary movements in animals.