Flies remember the time of day

Area of Science:

• Chronobiology
• Neuroscience
• Animal Behavior

Background:

• The circadian clock regulates daily rhythms in behavior and physiology.
• Animals exhibit time-specific memory, such as associating stimuli with particular times of day (time-place learning).
• The precise mechanisms underlying time-related learning and memory remain largely unknown.

Purpose of the Study:

• To investigate the mechanism of time-specific odor learning in Drosophila melanogaster.
• To determine if flies can form associations between odors and rewards at specific times.
• To explore the role of the circadian clock in this temporal learning process.

Main Methods:

• Drosophila melanogaster were trained to associate distinct odors with sucrose reward during morning and afternoon sessions.
• Training was repeated daily, and time-dependent odor preference was tested on the third day.
• Experiments were conducted under light-dark cycles, constant darkness, and constant light conditions, using wild-type and circadian clock mutant flies (per(01), clk(AR)).

Main Results:

• Drosophila demonstrated appetitive memory at the relevant time of day when conditioning events were separated by over 4 hours.
• Time-odor associations were formed in light-dark cycles and constant darkness, but not in constant light.
• Circadian clock mutants (per(01), clk(AR)) could learn odor-reward associations but failed to form time-odor associations.

Conclusions:

• Flies utilize temporal information as a cue in appetitive learning, forming time-odor associations.
• This time-odor learning relies on a period (per) and clock (clk)-dependent endogenous mechanism.
• The mechanism is independent of external light cues, highlighting the role of the internal circadian clock in temporal memory.