Swimming rhythm in decerebrated, paralyzed stingrays: normal and abnormal coupling

Area of Science:

• Neuroscience
• Animal Behavior
• Biophysics

Background:

• Locomotion is a complex behavior typically driven by a combination of central pattern generators and sensory feedback.
• Understanding the neural basis of rhythmic movements, like swimming, is crucial for deciphering motor control.
• Previous research suggests central pattern generators (CPGs) play a key role in coordinating rhythmic behaviors.

Purpose of the Study:

• To investigate the neural mechanisms underlying stingray swimming in the absence of sensory input (fictive locomotion).
• To analyze the properties of rhythmic motoneuronal activity during fictive swimming.
• To determine the role of intersegmental and intrasegmental coupling in generating swimming patterns.

Main Methods:

• Recording rhythmic motoneuronal activity from decerebrated, paralyzed stingrays.
• Comparing these recordings with electromyograms (EMGs) from the same animals.
• Analyzing parameters such as intersegmental delay, burst duration, and cycle period.

Main Results:

• A rostral-to-caudal sequence of alternating dorsal (elevator) and ventral (depressor) efferent activity was observed, constituting fictive locomotion.
• Intersegmental delay and burst duration remained linearly related to the swim cycle period, with intercepts near the origin, indicating constant phase coupling.
• Fictive swimming showed differences from active swimming, including fewer spontaneous sequences, a wider range of cycle periods, and increased burst duration:cycle period ratios.

Conclusions:

• Stingray swimming rhythm can be generated by neural circuits independent of phasic afferent input.
• Separate oscillator circuits for elevator and depressor motoneurons appear to exist within a single spinal segment.
• Intersegmental and intrasegmental coupling during fictive swimming is labile, suggesting complex network dynamics.