First published online December 10, 2003
Journal of Experimental Biology 207, 369-375 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00736
Antennal movements reveal associative learning in the American cockroach Periplaneta americana
David D. Lent1,* and
Hyung-Wook Kwon2
1 Arizona Research Laboratories, Division of Neurobiology, 611 Gould-Simpson
Building, PO Box 210077, The University of Arizona, Tucson, AZ 85721,
USA
2 Dept of Biological Sciences, 6270 Medical Research Building III,
Vanderbilt University, 465 21st Ave. South, Nashville, TN 37235,
USA
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Fig. 1. The visual associative learning paradigm employed to train restrained
cockroaches. (A) Experimental set-up. Restrained cockroaches were positioned
at the center of the arena. The distance from the head to the position of
visual and olfactory cues was 15 cm. Green and red LEDs (I.D. 3 mm) as visual
cues were positioned in parallel with an odor cue approximately 5° from
the midline of the head. (B) Learning performance was determined from
classical conditioning procedures. These are forward conditioning,
simultaneous conditioning and backward conditioning. The duration of the
conditioned stimulus (CS; light cue) was 2 s and that of the unconditioned
stimulus (US; odor cue) was 1 s. The time between the onset of the CS and the
US indicates inter-stimulus intervals (ISI). The ISI in simultaneous
conditioning was 1 s. The CS and US overlap and cease simultaneously. In
forward conditioning, the CS is given in its entirety and, after a 2-s ISI, is
followed by the US. In backward conditioning, an ISI of 2 s separates the US
from the following 2 s-long CS. There is no overlap between the CS and US in
forward and backward conditioning. (C) Basic training regimens consisted of
three pre-training trials, five training trials and either three testing
trials and three control testing trials, or three control testing trials and
three testing trials. A 2-s exposure to a red diode (650 nm) was used to
control for other incidental stimuli (see text).
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Fig. 4. Antennal projection responses (APRs) and learning performance of restrained
cockroaches during forward, simultaneous and backward conditioning procedures.
APRs during training (hatched bars) and testing (black bars) trials were
increased significantly in all three conditioning procedures compared with
pre-training (open bars) trials. APRs during training and testing in each
conditioning procedure were not statistically different and showed no
difference between forward and backward conditioning.
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Fig. 2. Patterns of antenna movements analyzed from video recording from the
simultaneous conditioning procedure. Antennal projection responses (APRs) are
the pointing behaviors of the right antenna to the cue position after a 2-s
stimulation during a 20-s observation period. The APR patterns are presented
in polar plots and the data are smoothed using five-point adjacent averaging.
Black dots represent the position of the right antenna at a given time, and
each point gives the continuous changes of antennal angles throughout the 2 s
light-on stimulus and the following 8-s observation period. Vectors (blue
arrows) show average points during the APR that vary significantly from
baseline. During pre-training (A1-A3), there are spontaneous antennal
movements but no APRs to the LED (green circle) position. During training
(B1-B5), antenna movements after LED onset show an increasingly precise APR to
the cue position. During testing (C1-C3), APRs were induced by the visual
stimuli and were very similar to the APRs during olfactory stimuli. This
animal showed no APR during the third trial of the test (C3). Control tests
(D1-D3) did not result in APRs to red LED stimulation.
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Fig. 3. Percentage of antennal projection responses (APRs) to olfactory, visual,
mechanical and auditory stimulation. The APRs were analyzed to determine the
unconditioned responses to different stimuli with possible arousing effects.
APRs to olfactory stimuli differed significantly from those to visual,
mechanical and auditory stimulation.
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Fig. 5. (A) Learning performances [assessed by percentage of antennal projection
responses (APRs)] were tested for up to 30 min after five training trials with
simultaneous conditioning (N=18). A high percentage of APRs to the
visual cue was retained 5 min, 10 min, 20 min and 30 min after training and
showed no statistical difference in these intervals. The responses at these
times were significantly different from pre-training and control test levels,
which were not significantly different. (B) Tests for long-term memory of APRs
(N=9). After training, APRs to the green light cue were tested for up
to 72 h. APRs were significantly different from those at pre-training even at
72 h, showing that cockroaches retained this learned behavior for long
periods. The response from 30 min to 1 h decreases by almost 30% but remains
stable for up to 72 h. The response at 72 h has decreased to almost 40%, which
is half of that observed at 30 min.
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© The Company of Biologists Ltd 2004
