Adaptive mechanisms in the elasmobranch hindbrain

Area of Science:

• Neuroscience
• Sensory Biology
• Comparative Physiology

Background:

• Elasmobranchs and teleosts possess mechanisms to suppress self-generated electrosensory noise (reafference).
• A modifiable efference copy mechanism, initially discovered by Bell, is central to this signal suppression.
• This adaptive filtering is observed in various brain regions, including the elasmobranch medulla, gymnotid electrosensory lateral lobe, and teleost mechanosensory lateral line nucleus.

Purpose of the Study:

• To investigate the adaptive filter mechanism responsible for suppressing electrosensory reafference in elasmobranchs.
• To elucidate the neural pathways and cellular substrates involved in this sensory gating process.
• To explore the universality and plasticity of this mechanism across different species and sensory modalities.

Main Methods:

• Intracellular recordings from projection neurons in the skate dorsal nucleus.
• Direct electrical stimulation of parallel fiber projections in the vestibulolateral cerebellum.
• Analysis of motor corollary discharge, proprioceptive, and electrosensory inputs.

Main Results:

• Motor corollary discharge, proprioceptive, and electrosensory signals independently and additively contribute to cancelling reafference responses in projection neurons.
• The cancellation signal is stable between behavioral bouts but can be rapidly modified (within minutes) to match changes in reafference.
• The adaptive filter's plasticity is primarily located at the synapses between parallel fibers and projection neurons.

Conclusions:

• The adaptive filter mechanism represents a universal form of efference copy, crucial for sensory processing in vertebrates.
• Plasticity at parallel fiber synapses in the cerebellum is a key site for modifying sensory cancellation signals.
• This mechanism allows for flexible and efficient processing of self-generated sensory information in diverse neural circuits.