Modulation of circuit feedback specifies motor circuit output

Area of Science:

• Neuroscience
• Systems Neuroscience
• Neural Circuits

Background:

• Bidirectional communication, including feedforward and feedback pathways, is prevalent in neural systems.
• The function and modifiability of feedback pathways remain largely unexplored in most neural systems.

Purpose of the Study:

• To investigate the role of feedback pathways in neural communication using the crab stomatogastric nervous system.
• To determine if peptidergic post-oesophageal commissure (POC) neurons trigger motor patterns by altering central pattern generator (CPG) feedback to projection neurons.

Main Methods:

• Examined bidirectional communication between projection neurons and CPG circuit neurons in the crab stomatogastric nervous system.
• Stimulated POC neurons and measured changes in feedback-mediated inhibitory postsynaptic currents/potentials (IPSCs/IPSPs) in projection neurons.
• Utilized dynamic-clamp techniques to inject feedback IPSPs of varying amplitudes into projection neurons.

Main Results:

• POC stimulation induced a long-lasting enhancement of feedback-mediated IPSCs/IPSPs in projection neurons, mirroring the duration of the triggered gastric mill rhythm.
• This enhanced feedback resulted from presynaptic modulation, as observed in projection neurons not directly activated by POC stimulation.
• Only enhanced feedback IPSPs (post-POC amplitude) elicited the specific motor pattern and enabled full expression of the gastric mill rhythm.

Conclusions:

• The strength of feedback synapses from CPGs to projection neurons is modifiable.
• Modifiable feedback pathways play a critical role in selecting and executing specific motor patterns.
• This study highlights the functional significance of feedback pathway plasticity in neural computation.