The generation of rhythmic activity in a distributed motor system

Area of Science:

• Neuroscience
• Marine Biology
• Animal Behavior

Background:

• Rhythmic neural activity underlies complex behaviors in many animals.
• The marine mollusk Pleurobranchaea exhibits rhythmic activity involving both its brain and buccal ganglia.
• The precise origin of this coordinated rhythmic activity has been debated.

Purpose of the Study:

• To determine if rhythmic activity in Pleurobranchaea originates from independent oscillators in the brain and buccal ganglia or a single locus.
• To investigate the role of cerebrobuccal connectives (CBC) in transmitting rhythmic signals.
• To elucidate the neural circuitry responsible for coordinated motor output.

Main Methods:

• Experiments involved isolated nervous systems of Pleurobranchaea californica.
• Tonic nerve stimulation was used to evoke rhythmic activity.
• Cerebrobuccal connectives (CBC) were interrupted to assess signal dependency.
• Simultaneous intracellular recordings were made from brain motoneurons and buccal interneurons.

Main Results:

• Motor output from the brain is dependent on continuous input from the buccal ganglia.
• The brain's rhythmic activity is driven by rhythmic generation within the buccal ganglia.
• Buccal interneurons projecting to the brain provide both drive and pattern for brain motor output.
• Tonic stimulation of CBCs can induce rhythmic activity in isolated brains due to axonal properties.

Conclusions:

• Rhythmic, coordinated activity in Pleurobranchaea originates solely from oscillatory circuits within the buccal ganglia.
• The brain receives and processes rhythmic signals from the buccal ganglia, but does not generate them independently.
• This study localizes the primary oscillatory locus for coordinated behavior in Pleurobranchaea.