What if hunger could turn down an animal’s heat alarm—not just making the warning quieter, but changing the alarm’s pattern so escape is no longer the default? To ensure survival, animals must detect and avoid noxious stimuli, such as harmful chemicals, toxic gases, or extreme temperatures.

These avoidance behaviors are essential for minimizing damage and guiding appropriate behavioral responses. The nematode Caenorhabditis elegans can produce robust innate escape behaviors and modulate these responses according to external and internal regulatory cues.

Animals must continuously adapt their behavioral outputs in response to changes in internal state, including nutritional state. In Caenorhabditis elegans, starvation induces a profound and progressive suppression of heat-avoidance behavior. The thermoresponsive sensory neurons called AWCs mediate robust heat-evoked reversals over a broad range of stimulus intensities.

They use two signals, each covering distinct heat-intensity ranges. Prolonged food deprivation led to a striking progressive reduction in heat-avoidance responses, with responses after six hours of starvation approaching the animals’ usual spontaneous reversal rate. This suggests a robust inhibition of danger-avoidance behavior.

The reduction in heat-avoidance response persisted even when food odor was present, indicating that the effect is driven by the internal starvation state rather than external smell. The setup makes the comparison clear: each longer food-free interval is tested against the same steadily increasing heat challenge, while the starting spontaneous movement is measured separately.

The ASI neurons are specifically required for starvation-dependent modulation of heat-avoidance behavior. Under these conditions, AWC neurons are the primary driver of heat-evoked reversals during early food deprivation, while ASI neurons selectively mediate their suppression during prolonged starvation.

Under early food deprivation, AWC neurons respond consistently to heat, but under prolonged starvation they enter a heterogeneous and less predictable response mode. Starvation does not simply attenuate AWC calcium responses; it fundamentally alters their dynamics, shifting from a largely deterministic excitation profile to a heterogeneous regime characterized by decreased and variable responses.

This transformation in thermal encoding might underlie the behavioral plasticity observed during starvation. Prolonged starvation transforms heat-evoked AWC calcium responses from a stereotyped, intensity-dependent activation pattern to a heterogeneous, less predictable regime.

This shift is not merely a quantitative attenuation but a qualitative reorganization of response states, including frequent calcium downregulation or variable traces. In the same animal, a single stimulus train can include both calcium increases and decreases.

In an early food-deprived state, AWC neurons may signal heat intensity in a consistent and reliable manner to promote aversion. Under prolonged starvation, dampened and variable AWC responses may bias the animal away from escape behaviors, prioritizing food-seeking over threat avoidance.

Starvation profoundly modulates heat-avoidance behavior by engaging distinct neurons, altering neural response dynamics, and mobilizing opposing signal pathways. This behavioral change depends on a shift in the internal state that is not rescued by food-associated olfactory cues.

AWC and ASI neurons work to integrate thermal and nutritional cues into an adaptive behavioral output. In the face of acute harmful stimuli, animals typically favor rapid escape to minimize injury. However, under prolonged food deprivation, that protection may come at the cost of missed opportunities for locating food.

By reducing the sensitivity or reliability of danger-avoidance pathways, particularly through changing AWC output, Caenorhabditis elegans may adopt a more exploratory behavioral mode, tolerating greater risk to increase the chances of finding food. This trade-off between protection and exploration mirrors similar state-dependent shifts observed in other species, suggesting that internal metabolic needs can reshape threat evaluation and behavioral responses.

In hungry worms, the nervous system weakens and reshapes heat avoidance, apparently favoring exploration for food over perfect protection. The finding shows how body needs can change both what a danger signal means and what action follows.