Behavioural and neurogenetic evidence for emotion primitives in the fruit fly Drosophila from an open field test.

Activation of reward-related neurons in Drosophila melanogaster decreased wall-following in the open field test, while inhibition increased it, supporting emotion-like modulation.

• Why it matters: It is largely undefined whether evolutionarily conserved “emotion primitives” exist in insects, limiting how well insect genetics can model vertebrate-like affective building blocks.
• What they did: Wildtype and transgenic flies were tested in the open field test, using wall-following and total walking activity as independent behavioural indicators across aversive and positive conditions, with neuromodulatory genetic manipulations and ethanol or diazepam treatments.
• The result: Wall-following and total walking activity were modulated in opposite directions by stimulus valence (generally increased wall-following under aversive stimuli and decreased under positive conditions), enabling Drosophila to be used to dissect neuronal and neurochemical substrates of emotion primitives.

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