Temperature modulates the tuning properties of small target motion detector neurons in the dragonfly visual system

Dragonflies are poikilothermic animals with limited thermoregulation; therefore, their entire bodies, including the brain, experience a range of temperatures during their daily activities.^1,2 These flying insects exhibit hunting prowess, pursuing prey or conspecifics whether in direct sunlight or under the cover of cloud.^3,4 Likely to underlie these aerobatic feats are the small target motion detector (STMD) neurons.⁵ These visual neurons are sensitive to target contrast and tuned to the target's size and velocity, with some neurons exhibiting complex predictive and selective properties, well suited for prey interception and feeding amid swarms.^3,4,6,7,8,9 Increased temperature can modulate the biochemical processes underlying neuronal processing, increasing sensitivity and quickening the responsiveness of insect photoreceptors and downstream optic flow neurons,^10,11,12 while in other neuronal pathways, compensatory processes have been shown to account for temperature changes.^13,14 We determined the ethological range of temperatures experienced by the dragonfly, Hemicordulia tau, in its natural environment. Across this behaviorally relevant range, we showed increased temperatures having a large 8.7-fold increase in the contrast sensitivity of STMD neurons. However, suppression of responses to larger targets was unaltered. STMD tuning for target velocities was changed remarkably, not only increasing the optimum but extending the fastest velocities encoded by an order of magnitude. These results caution against interpreting functionality underlying spike rates at constrained, experimental temperatures. Moreover, they raise intriguing new questions about how information is represented within the brain of these flying insects, given the relationship between visual stimulus parameters and neuronal activity varies so dramatically depending on current environmental conditions.