In 1998, NASA flew crickets on Neurolab to study how spaceflight affects developing nervous systems; across the 16-day mission, they joined about 2,000 animals in space

On April 17, 1998, space shuttle Columbia took off from NASA's Kennedy Space Center with a crew of seven people and some very special passengers. Onboard Spacelab were 2,000 animals, including rats, mice, snails, fish and crickets, making Neurolab one of the largest collections of living organisms ever sent into space, according to NASA's official mission archive. This 16-day mission, STS-90, focused on one question: how does spaceflight affect the developing brain and nervous system?

Why crickets made the cut

Sending crickets into space might seem like a strange choice for brain research, but crickets possess a simple, well-mapped gravity-sensing system. Unlike humans, crickets do not have gravity receptors deep within the inner ear; instead, their receptors are located outside the body. The nerve cell, known as a position-sensitive interneuron, provides a direct connection from the receptors to the brain. According to the paper ‘Crickets in space: morphological, physiological and behavioral alterations induced by space flight and hypergravity,’ this simple connection made crickets a suitable model organism to study changes that take place when the gravity input is missing.


Inside the CRISP experiment

The experiment was called CRISP, short for Crickets in Space. Researchers sent eggs and larvae at various stages of development of the common house cricket, Acheta domesticus, to compare the animals that developed partly on Earth and those developing entirely in space. The study's methodology states that eggs and first-, fourth-, and sixth-stage larvae were used in the experiment.

What the researchers actually found

The findings suggest a more complicated picture than a simple system failure in space. The study reports no observable structural differences in the nervous tissue it examined, including neuromuscular junctions and cerebral neurons, after exposure to space conditions. However, the functioning of the position-sensitive interneuron was altered. It was much less sensitive to weightlessness, and the space-grown animals had higher levels of a related signaling molecule called a neuropeptide than those grown on Earth.

Despite that, the crickets' behavior remained largely unchanged. Their compensatory reflexive movement of the head, which assists them in orienting themselves relative to gravity, responded poorly to both the zero-gravity environment and the increased gravity used for comparison on the ground. Researchers observed that, after returning from space, the crickets appeared to rely on other senses, including touch and vision, to adapt to gravity despite changes in the basic gravity circuit.

Why this connects to human spaceflight

It may be difficult to connect crickets to people, but the way nervous system development responds to the absence of gravity may also be relevant to humans. According to a 2021 review published in the journal Frontiers in Neural Circuits by scientists at McGill University and Johns Hopkins University, almost 70 percent of astronauts face problems of impaired balance, motion sickness, and coordination issues during the first few days of their journey in outer space and right after returning to Earth. The study, ‘Challenges to the Vestibular System in Space,’ explains that such effects happen because the human vestibular system has to reorient itself whenever there’s a sudden change in normal sensory input. Studying a simpler animal like a cricket allows the researchers to focus on what occurs on the cellular level because it is much more difficult to do that within the human brain. Such research may help scientists better understand and address astronaut disorientation during future missions to the Moon and Mars.

A mission built for the brain

Neurolab was NASA's contribution to the 'Decade of the Brain' campaign, launched by the United States Congress and President George H.W. Bush in 1990, which aimed at expanding the scientific knowledge about the functioning of the nervous system. Alongside the CRISP experiment, there were 25 other experiments on board the spacecraft, organized into eight groups. Of these experiments, eleven were carried out on humans, and 15 were devoted to animal research. The Neurolab mission is considered one of NASA's largest biological expeditions and addressed brain questions that scientists are still studying today. On the outside, the crickets that flew on Neurolab returned looking the same, but inside their tiny nervous systems, something had truly changed, a reminder that gravity influences biology in ways not always visible from the outside.