Not as Dumb as You Thought: Fruit Flies

This piece, by Onno Berkan, was published on 10/22/24. The original text, by Snyder et al., was published by Nature Neuroscience on 07/02/24.

A recent Berkeley study investigated how the presence and behavior of human experimenters influence the neural activity of hippocampal neurons in Egyptian fruit bats during experimentation. The researchers found that neural responses were significantly modulated by the experimenters, both when the bats were flying and stationary.

The experiment involved two main parts: first, bats freely flew to one of two human experimenters for a reward. Second, the bats remained stationary while the humans approached them to feed or handle them. The researchers precisely tracked the positions of both the bats and humans throughout the experiments.

Analysis of the neural data revealed that over a third of the recorded bat hippocampal neurons carried significant spatial information about at least one experimenter's position. Interestingly, most neurons responsive to experimenter identity were selective for only one of the two experimenters. There was little overlap between neurons modulated by stationary humans during bat flight and those modulated by moving humans while bats were stationary, suggesting largely independent neural populations for these conditions.

The study also found that neural responses to the experimenters were stable over time, indicating the modulation was present from the beginning of the session rather than emerging gradually. This suggests the bats rapidly formed associations between the experimenters and their spatial locations or behaviors.

These findings highlight the significant influence that human experimenters can have on neural activity in animal subjects, even when not directly interacting. The researchers emphasize the importance of controlling for and potentially eliminating these effects in neuroscience experiments involving animal subjects. They suggest explicitly tracking experimenter behavior and position may be necessary to fully understand and account for these influences, making data processing much more difficult.

The study was limited to female Egyptian fruit bats and two human experimenters, so further research is needed to explore these effects across different species, sexes, and experimental conditions.

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