A Worm to Remember
A Comparison of Conditional Learning in
Planaria Based on Monopolar Orientation to
a Specific Electrode
Emily Yuan
Under the direction of
Michael Levin, Ph.D
Debbie Sorocco, RA I
The Forsyth Institute
September 11, 2002
Introduction
Why Use Planaria to Study Learning
and Memory Mechanisms?
Planaria Anatomy
The planarian is the simplest living
animal whose body-plan exhibits
bilateral symmetry and cephalization.
The ratio of the brain weight to body
weight is similar to that of a rat!
system
bilateral
symmetry
Regeneration
Heads or Tails?
Comparison of Anterior/Posterior Memory Retention After
Regeneration
1. Classical Conditioning
2. Induced Fission
push button
6V battery
light
source
electrodes
3. Regeneration
4. Retest and Compare
Head vs. Tail
Methodology
Classical Conditioning Technique:
- Conditioned Stimulus (CS) = light
- Unconditioned Stimulus (UCS) = shock
- Conditioned Response (CR) = longitudinal
body contraction
- Trial = 2 sec of CS followed by 1 sec of UCS
- Successful trial = CR expression before
onset of UCS
Electrode Specific Experiment
N = 12 Dugesia dorotocephala
- 6 facing anode during
trial
- 6 facing cathode during
trial
A switch controlled direction of
current, allowed either electrode
to be anode or cathode,
depending
on
planaria
orientation.
Results
% of Conditioned
Responses
Anterior Orientation
During Conditioned Contractions
100%
90%
80%
70%
60%
50%
40%
30%
Cathode
Anode
20%
10%
0%
A-1
A-2
A-3
A-4
A-5
A-6
A-7
A-8
B-1
B-2
Worm
Preliminary experiment (no control over anterior
orientation): 68% of total CR expression occurred
when anterior was oriented toward anode
Results (continued)
Number of Conditioned Responses in Anode vs. Cathode
Orientated Planaria
4.5
Number of Conditioned
Responses (out of 25)
4
3.5
Anode Orientation
3
2.5
+
+
_
_
2
_
1.5
+
Cathode Orientation
1
0.5
_
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Trial Set Number
Comparison of changes in mean frequency of CR
expression over fourteen sets of 25-trials for anode and
cathode oriented planaria. (p<<0.01)
+
Conclusion
• Significant increase of CR expression when
planaria were oriented toward the anode
• Supports published data that:
- planaria can learn
- orientation in electrical field influences
rate of learning
Future Research:
These results provide information to design more effective
protocols for future classical conditioning experiments