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TO SWIM OR NOT TO SWIM: NEUROBIOLOGY OF LEECH SWIMMING

Introduction

Define behavior in terms of synaptic interactions between identified neurons.
Is this sufficient?

Leech Anatomy and Central Nervous System

Swimming Leech
Cross Section of a Leech
Central Nervous System
Segmental Ganglion - ventral surface

Concept of identified neurons

How Does One Identify Neurons Involved in Swimming?

Traditional Approach: Semi-Intact preparation.

Simultaneous intracellular recording from neurons during 'fictive' behavior.

Result: Static connectionist models

- define the functional limits of the network
- dynamic complexity of network is lacking and unexplained

Organization of the Leech Swim Generating System

Neuronal basis of swimming has progressed to the point where swim initiation following body wall stimulation can be traced, neuron to neuron, from the sensory neurons that perceive the stimulus to motor neurons that produce the swimming movements.

Summary Diagram - connectionist model!!

Five functional classes of neurons (at least) comprise a swim-generating pathway.

Motor Neurons
Oscillator Neurons (Central Pattern Generator)
Swim-Gating Interneurons
Trigger Neurons
Mechanosensory Neurons (P Cell)

What's Missing?? - many things

Mechanism underlying activation of swim-gating and oscillator neurons - Trigger Neurons
Swim variability - Trigger Neurons



What do I mean by swim variability?