Two Compasses in the Central Complex of the Locust Brain

Area of Science:

• Neuroscience
• Animal Behavior
• Sensory Ecology

Background:

• Migratory insects utilize celestial cues, including the sun's position and polarized skylight, for spatial orientation.
• The central complex (CX) in insect brains contains neurons that encode sky compass information.
• In desert locusts, the CX represents polarized light (E-vector) and the sun's azimuth topographically.

Purpose of the Study:

• To investigate if solar azimuth is represented topographically in the desert locust's central complex (CX).
• To determine how neurons in the CX encode the azimuth of an unpolarized light spot, potentially representing the sun.
• To explore the relationship and interaction between the celestial polarization compass and the solar azimuth compass within the CX.

Main Methods:

• Intracellular recordings from eight types of CX neurons in male and female desert locusts.
• Stimulation using polarized blue light from the zenith and a rotating unpolarized green light spot at various elevations.
• Analysis of neuronal responses to correlate activity with E-vector orientation and solar azimuth.

Main Results:

• CX neurons did not encode the elevation of the unpolarized light spot.
• Two types of columnar neurons exhibited a linear correlation between CX slice innervation and azimuth tuning to the unpolarized light spot.
• Both E-vector orientation and solar azimuth are represented topographically in the CX but are not directly linked, interacting nonlinearly.

Conclusions:

• The central complex (CX) in desert locusts contains a topographic representation of solar azimuth, functioning as an internal compass.
• The CX processes distinct celestial compass cues (polarized light and solar azimuth) separately.
• These compass systems interact in a cell-specific and nonlinear manner within the CX, contributing to heading direction signaling.