Electrically evoked behaviors: axons and synapses mapped with collision tests

Area of Science:

• Neuroscience
• Neurophysiology

Background:

• Previous studies utilized double-pulse methods to characterize axon bundles and their properties like refractory periods and conduction velocities in behaving animals.
• Directly stimulated axons were identified by their activation leading to specific behaviors.

Purpose of the Study:

• To introduce and describe new collision effects, specifically asymmetric collision, for locating synapses.
• To determine the direction, timing, and reliability of synaptic transmission using asymmetric collision parameters.
• To construct circuit diagrams of neural systems by applying collision tests.

Main Methods:

• Utilizing symmetric and asymmetric collision effects to map axon bundles and locate synapses.
• Applying asymmetric collision effects between acoustic stimuli and electrical pulses to define auditory startle pathways.
• Analyzing the direction, time, and strength of asymmetry to infer transmission properties.

Main Results:

• Five axon bundles were localized using symmetric collision effects in turning systems.
• Evidence for two synapses was provided through asymmetric collision effects in turning systems.
• Three fast, reliable synapses were located in startle response systems using asymmetric collision.
• Asymmetric collision effects precisely defined the timing and location of the acoustic volley in hindbrain sites for acoustic startle.

Conclusions:

• Asymmetric collision effects offer a powerful method for precisely locating synapses and mapping neural circuits.
• This technique enables the construction of detailed circuit diagrams in behaving animals, particularly for systems mediating turning and startle responses.
• The findings highlight the utility of collision tests for understanding synaptic function and neural network organization.