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Leech Talk
TO SWIM OR NOT TO SWIM: NEUROBIOLOGY OF LEECH SWIMMING
Introduction
- Neuronal basis of behavior
- Understand how information (neural code) propagates through the nervous system to produce a given behavior in response to a specific stimulus.
- Problem: What does 'understand' mean?
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?
Source of Variability
- Hormonal?
- Neurons in the head and tail ganglia
- Neurons in the Head/Tail Ganglia Add Another Layer of Control / Complexity
Analysis of Head / Tail Ganglia Control of Swimming
Goal: Understand how neuronal activity propagates through the nervous system to produce a given behavior in response to a specific stimulus
Results from Traditional Approach
Inhibitory Control (Swim-Inactivating System) - Cell SIN1; unknown cells
Cell SIN1: Activity pattern during swimming.
Cell SIN1: terminates swimming
Swimming depends of the interactions between the swim-activating and inactivating systems, and their respective effects on the segmental swim-generating network.
Goal Achieved? - partially!
Time Series Analysis (Signal Processing): A Computational Approach
use mathematical tools to tell us about the dynamics of the data data = sequence of voltage measurements in time (time series) Goal: Use time series analysis to quantify features of the physical system - leech CNS. Compare results with network model generated from traditional approach.
1) Is there an information pattern or neuronal firing sequence required for initiating swimming?
Quantify pattern of neuronal activity that predicts swimming.
Is it dependent on the manner by which swimming is elicited? (triggered vs. spontaneous)
2) Does the nervous system have to be in a specific state for swimming to be triggered?
Raw Data - single trials
Raw Data - multiple trials
Tr1 Stimulation: Swimming vs. Non-Swimming Trials
Time Series Analysis
Post-Stimulus Time Histogram
CONCLUSIONS:
1) Systematic analysis (traditional approach) of leech CNS has resulted in a network model that provides significant insights into the neuronal basis of swimming.
2) Just starting to use time series analysis to characterize and quantify the variability observed in the swim generating network.
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