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Lab#2 Animal_behavior_Renn_2007_REVISED-Fri.
NAME ________________
“Learning” in Planarians
Learning is described as a process by which we acquire
knowledge about the world. In experimental science, the way
we can measure this phenomena is by a behavioral bioassay.
Learning can be defined as a change in behavior due to
experience. This definition excludes behavioral changes due to
developmental maturation or by drugs. The behavioral change
has to come from exposure to the environmental medium that
has acted on sensory systems to produce stimuli. While some researchers exclude very
simple experience-induced behavioral modifications from the definition of “true
learning”, most neuroscientists identify the category of non-associative learning to
include sensitization, habituation, and dishabituation.
There are two types of sensitization. (1) a stimulus that originally elicited a weak or no
response, evokes an increased response with repeated presentations. or (2) following one
stimulus, a different stimulus evokes an increased response than would have been
otherwise observed. For example, after a very loud crash sound, smaller noises can startle
a person, which otherwise would go almost unnoticed.
In the case of habituation, repeated presentation of the same stimulus produces
decreasing responses to it. In the example of the loud crash, if it keeps sounding
repeatedly every twenty seconds, the startle to it will decrease with additional
presentations.
Behaviorally, dishabituation is very much like the 2nd form of sensitization in that one
stimulus evokes an increased response to another stimulus, however dishabituation is
different from sensitization because it restores the strength of a response that was
previously decreased by habituation.
Because the same stimulus can evoke an increased response in either habituated or nonhabituated responses, dishabituation was thought to represent a special instance of
sensitization in which the increase in response is simply superimposed on a habituated
response level. However, by considering the ontogeny (see your 4 questions of animal
behavior) researchers were able to determine that dishabituation and sensitization reflect
separate mechanisms (see your 4 questions of animal behavior). Rankin and Carew
(1988) studied the withdraw reflex in the sea slug Aplysia throughout development and
found that dishabituation was present in all developmental stages, but sensitization was
not seen until several weeks later. The identification of molecular mechanisms that
distinguish between sensitization and dishabituation continues to be an area of current
research (e.g. Mongeluzi and Frost (a Reedie), 2000; Hawkins et al., 2006) and will be
presented in lecture.
For the purpose of this lab, we will distinguish between sensitization and dishabituation
according to a behavioral definition. We will refer to any stimulus that restores (or
exceeds) normal response to stimulus as a “dishabituating” stimulus only when that
animal has previously been habituated (i.e. trained with repeated stimulus that resulted in
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a decremented or reduced response). Much of the behavioral analysis, as well as the
study of the molecular mechanisms underlying non-associative learning, was conducted
using the marine mollusk (slug) Aplysia (visit Steve Arch’s lab if you would like to see
one). The nervous system of the slug is easily accessible and they have very large
neurons for electrophysiology, however these animals are difficult to maintain in lab so
we will use a different model organism to study simple forms of learning.
simple learning
18
A
B
C
D
16
response strength
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12
10
another stimulus
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2
0
1
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5
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7
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21
trail
number
trial
number
Figure 1 presents the average response strength determined for three animals that were
each tested with a repeated stimulus for 21 trials (error bars indicate standard error). In
your own words, in your lab notebook, describe which simple form of learning is
represented during phase A, B, C and D.
Planarians belong to the order Tricladida (named for their three branched gut structure)
in the phylum Platyhelminthes (Flatworms). Although this phylum has retained a sac like
gut with only one opening, flatworms are triploblastic (have tissues derived from three
embryonic germ layers) but have no coelom. Planarians can be found in most bodies of
fresh water, they are the free-living relatives of parasitic flatworms such as tapeworms
and flukes. Most planarians are hermaphrodites and can therefore reproduce sexually as
either males or females (simultaneously). They also reproduce asexually by fission. In
nature they do this by holding tight to the substrate at the tail end while the head end
crawls away, but in the lab they show remarkable regenerative capabilities and have
recently become a powerful model for cell differentiation (for a review see Salo, 2006).
More significant to their utility in research on behavior, these animals have a central
nervous system. In the head of a planarian, there is a concentration of nervous tissue that
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can be called a “brain” which allows more complex behaviors. By virtue of abundant
sensory cells, specialized sense organs and a centralized, cephalized nervous system,
planarians show varied behavior with rapid and precise responses. Planarians are
negatively phototactic (avoid light), positively rheotactic (move toward water current)
and respond to different chemical cues. In lab we will test the hypothesis that
planarians exhibit simple forms of learning.
When fully extended, a planarian can readily be characterized as having a “head” and
“body”. When fully contracted, a planarian appears to be an undifferentiated, roughly
circular blob. A planarian crawling in a Petri dish initially exhibits a reflexive contraction
response when water is dropped onto or near its anterior region (hereafter referred to as
its head). This response declines in magnitude over repeated trials but shows partial or
full recovery following moderate physical agitation (dishabituation).
Table 1. Scoring System for Planarian for Contraction Response
Score Behavior
Description
0
No response
The planarian remains in extended swimming position
1
Simple flinch
The planarian responds but without visible shortening
of the body
2
Head Retraction Visible widening of the body and decrease in head
distinction
3
Full Contraction Near or complete loss of head-body distinction
MATERIALS:
Each team of 4 students will have:
plastic disposable pipettes
100 – 1000 micropipettor + blue tips
Petri dishes (60mm)
15 flat worms (12 experimental, 3 practice)
Planarian water in a 15 ml tube
2 white plastic squares
stopwatch
instructions for setting a stopwatch to beep every 10 seconds:
upper left button = Reset \Select
upper right button = Start\Stop\Set
Lower right button = Chrono/Timer
Chrono/Timer switch from Chrono to Timer
Select 3 times
Set 1 time
Select 3 times
press-Start
Stopwatch will beep every 10 seconds and count the number of 10-second intervals.
press-Stop
Reset
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PROCEDURE
Practice drawing the planarian into and expelling it from the disposable pipette gently.
Draw a substantial amount of water into the plastic pipette along with the planarian to
prevent it from clinging to the pipette’s inside surface. This is how you will move one
animal at a time in and out of the experimental arena. By rapid repetition, this is also the
stimulus that will be used for sensitization and dishabituation.
Working in teams of 4 students, establish interobserver reliability.
Get three practice worms
 Fill the Petri dish bottom with 3 ml. of Planarian water (use a 100-1000
micropipettor to measure). This is sufficient to submerge the planarian but not
allow it to avoid the impact of a water stimulus. (Before adding the worm shake
the water to break surface tension and cover the bottom of the plate)
 Using a practice planarian before beginning the experiment proper, transfer one
planarian to the center of the Petri dish on top of the white plastic square.
 Set the stopwatch to beep every 10 seconds. (instructions above)
 For each trial, expel a drop of water from the disposable pipette onto the
planarian’s head from approximately 1 cm above the water’s surface.
 Draw the stimulus water from the Petri dish so as not to add more volume.
Increasing volume would introduce a confounding factor.
 Repeat this for 5 trials at 10 second intervals.
 In your lab notebook, record your response using the scoring system in table 1.
 As a team, compile the scores in the following table to calculate reliability.
Trial / 1
2
3
4
5
Obs.
1
2
3
4
____ ____ ____ ____ ____ How many observers agreed on each trial?
Interobserver-reliability is calculated as
(total # in agreement)/ (total # of observations) * 100
In order to achieve 90% inter-observer reliability, your team must score 18 agreements
for the set of 20 observations.
Discuss your results. Repeat the test until the team achieves 90% interobserver reliability.
Experimental Methods
A habituation trial will be conducted with 10 second intervals for 15 trials. The 10
second interval should allow time for the planarian to resume its gliding motion. Be
careful to not disturb the Petri Dish, if the dish is disturbed, skip this data point, because
the individual has received additional stimulus that is not part of the experimental design.
Dishabituation/Sensitization stimulus: The planarian is stimulated by drawing it into
and expelling it from the disposable pipette 5 times in rapid succession. This stimulus
typically produces the effect without risk of injury to the subject. If you are working with
a very large planarian you may need to cut the tip off of the disposable pipette to provide
a large enough opening to not damage the animal.
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Protocol – Read through the Protocol and make a plan of attack. Use a work
flowchart or outline in your lab notebook, and decide who will drop the water, who
will do the recording, and be sure you know how to set the timer.
Experiment 1: Habituation/Dishabituation Protocol
Get 6 flatworms.
Each team of 4 will habituate 6 individual planarians in separate dishes with repeated
water drops. The team can split into pairs. The pairs should work in parallel, each
habituating 1 of the group’s planarians at a time. One student administers the water drop
while the other records the response. The recorder should start the timer when both the
two droppers in your team are ready, and the recorders should enter data directly into the
lab notebook.
It is important to run these protocols in parallel so that the “no treatment” in the control is
the same amount of time as the dishabituation stimulus.
HDH
HCH
Three of the habituated planarians will be “dishabituated” with the dishabituation
stimulus immediately following the habituation trials. As soon as this animal has resumed
its gliding motion, immediately repeat the full 15 trials for habituation.
Trial 1 … Trial 15
dishabituation
Trial 16 … Trial 30
The other three of the habituated planarians will be the “control group” and will not be
treated with the dishabituation stimulus. This animal will sit undisturbed for a time equal
to the dishabituation stimulus. This animal will then be retreated with the full 15 trials for
habituation in parallel with the experimental animal.
Trial 1 … Trial 15
no treatment
Trial 16 … Trial 30
After the experiment, return the used Planarians to the jar labeled “used planarians”.
Experiment 2: Sensitization/Habituation/Dishabituation/Habituation Protocol
Get 6 new flatworms
BEFORE you do anything, do one water drop test to get a baseline measure for each
animal (experimental and control). Record this baseline as trial 0.
Each team will “sensitize” 3 new individual planarians with the disposable pipette and
immediately habituate these animals with the repeated water drop stimulus. Each team
will also run 3 control planarians that do not receive the sensitization stimulus.
SHDH
CHCH
Three of sensitized/habituated planarians will be “dishabituated” with the disposable
pipette and then retested for persistence of habituation with repeated water drops.
Trial 0
sensitization Trial 1 … Trial 15 dishabituation
Trial 16 … Trial 30
The other three control planarians will be the “control group” and will not be treated with
the sensitization or dishabituation stimulus. This animal will sit undisturbed while the
other pair in your team is sensitizing and later dishabituating their test animal. This
animal will then be retreated with the habituation trial in parallel with the experimental
animal.
Trial 0
no treatment Trial 1 … Trial 15 no treatment
Trial 16 … Trial 30
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DATA ENTRY StatView Instructions
Log in to the computer and the Courses Server as YOURSELF.
Enter your data before starting the statistical analysis section.
Drag the Expt 1+2 worm data template data template file from the Courses Server to
your desktop.
Open the Expt 1+2 worm data template that is on your desktop.
Save As Joe_Th_Carey or Sue_F_Ned etc.
Enter your results, one row for each worm, in the “Joe_Th_Carey” file on your desktop.
Save this file on your desktop and also put this file in the drop box.
You will need this file for part A of the assignment.
The class will also be waiting for your results for the class data file.
STATISTICAL ANALYSIS
What are we controlling by including a control group that does not receive the stimulus?
Was there an experimenter artifact? There should be no difference between the
experimental and control animals prior to the dishabituating stimulus. But, there could be
a strong effect of water dropping technique that might cause a different degree of
habituation. In some experimental designs it is important to randomize all sources of
variation, but sometimes it is not possible, or it may introduce too much confusion to the
experimental design. When it is not possible to control these effects or randomize the
design, it is important to examine the data to ensure that significant results are due to
biology that you are studying and not due to your experimental design.
Below are listed several interesting questions you could answer by interrogating the data
from this very simple experiment. The questions are listed on the left and the statistical
tests are listed on the right. In your group decide which tests you would need to do to
answer each question. If your group has additional questions, write them in your lab
notebook and decide what parts of the data set you will need to use to answer them.
Experiment 1-Which comparison and statistical test would you use with data from
experiment 1 in order to answer the following questions?
Match A-E with 1-5.
1) Did the animals habituate to repeated stimulus?
A) paired t-test trial 1 compared to trial 2, 3,
or 4.
2) Did the dishabituation stimulus cause a significant
B) paired t-test for the first mean habituation
increase in response?
score compared to the second mean
habituation score for experimental animals.
3) Is the response to stimulus fully restored by the
C) paired t-test trial 16 and trial 1
dishabituation stimulus? (not significantly different)
experimental animals only.
4) Is habituation after dishabituation the same as the
D) t-test (trial 16 minus trial 15)
original habituation? (use mean score for 15 trials as
experimental compared to control.
the characteristic of mean habituation)
5) Did the animals show sensitization?
E) paired t-test for trial 1 and trial 15 all
(According to the earlier description of sensitization,
animals.
how is this different than the sensitization stimulus that
we use in experiment 2?)
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Experiment 2- Which comparison and statistical test would you use with data from
experiment 2 in order to answer the following questions about sensitization?
Match A-E with 1-5.
1) Did the sensitization stimulus cause an increase
A) paired t-test (trial 1 minus trial 0) compared to
in response?
(trial 16 minus trial 15) experimental animals. **
2) Does the dishabituation stimulus cause a
B) compare the animal’s mean score for the entire
significant increase in response to stimulus? (same
habituation session before the dishabituation
as in experiment 1)
stimulus to the mean score for the entire habituation
session afterwards using a paired t-test and
experimental animals only
3) Does the dishabituation stimulus cause a greater C) paired t-test compare trial 0 to trial 1
difference in response than the sensitization
experimental animals only.
stimulus?
4) Is the habituation after dishabituation different
D) t-test (trial 16 minus trial 15) experimental
than habituation after sensitization? (use mean
compared to control.
score for 15 trials as the characteristic of mean
habituation)
5) Did the sensitization stimulus cause greater
E) t-test (trial 1 minus trial 0) experimental
sensitization than simple repeated stimulation with
compared to control.
the same stimulus?
Combining Data, a “Meta Analysis” Which comparison and statistical test would you use
with data from experiment 1 and experiment 2 in order to answer the following questions
about sensitization?
Match A-B with 1-2.
1) Is habituation following dishabituation
A) compare the mean for trials 16 through 30
stimulus affected by an earlier sensitizing stimulus? experiment 1 experimental animals compared to the
mean for trials 16 through 30 experiment 2
experimental animals.
2) As a necessary control for a meta analysis you
B) t-test trial 1 experiment 1 compared to trial 0
must show that the animals used (and baseline
experiment 2. **
conditions) in the two experiments are not different.
--Why do we not use a “paired t-test” and only a “t-test” in some of these analyses?
--Record your reasoning in your lab notebook and include any other interesting
comparisons you could do to answer additional questions about the simple learning
in planarians.
** tests marked with a double asterisk are tricky, ask for help if you need it.
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HAND IN (Due at the end of lab)
A: Hand in two graphs of your team’s data, one for experiment 1 and another for
experiment 2. On each graph, the average score for the 3 experimental animals and
also the average score for the 3 control animals should be plotted on the Y-axis and
the trial number for that experiment should be plotted on the X-axis.
After you have entered your data and put your file in the drop box begin this part of the
assignment.
StatView Instructions for data graph
Drag the score by trial data template from the Courses Server to your Desktop.
Open the score by trial data template file that is now on your Desktop.
Copy the scores for trials 0-30 for all 6 animals in experiment 1 from your saved version
of Expt 1+2 worm data template (Joe_Th_Carey) on your desktop.
In the score by trial data template, select the entire area where the data will go and use
Paste Transposed from the Edit menu to move trial scores from horizontal to vertical
form.
The text entries (habituation, sensitization, dishabituation) in your data set will
automatically be assigned numbers as placeholders, but you DO NOT want to graph
these, so you must first delete them. Find the trial number 15.5 and delete the placeholder
numbers in the data field.
Repeat these steps for all 6 animals in experiment 2.
The placeholder numbers that need to be deleted now correspond to trials 0.5 and 15.5.
You will calculate the mean for the 3 control and the three experimental animals for each
experiment separately in the appropriately named 4 columns to the far right.
Use the Source:Dynamic Formula to enter the formula to calculate the average score for
each set of 3 worms.
Choose Analyze / New View to make the graphs.
Using Bivariate Plots / Line Chart plot the average scores for the experimental and the
average scores for the control animals on the Y axis (Y Variable) and plot the trial# for
the appropriate experiment on the X axis (X Variable)
B: Choose 3 hypotheses from above (or ones generated by your team).
1) Apply the appropriate statistical test to the class data set.
2) Present your results in a graph.
3) Include a figure legend to briefly state the method (not the result).
3) Summarize the results of your statistical analyses and explain whether
your data clearly answer the question you asked.
Graph your team’s data and discuss the hypotheses that you wish to test before going on
to the statistical analysis. You will have to wait for the complete lab dataset in order to
have a sample size appropriate for the t-tests.
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General StatView Instructions for t-tests
The exact steps that you use will depend upon the questions you choose to answer.
Both types of t-tests can be done using the worm_data_day_room file (example:
worm_data_T_Ned) found on the Courses Server.
When you need to separate experiment 1 from experiment 2, you will use Manage->
Create Criteria
When you need to separate experimental from control values, you will select the
expt/control column and use the Split By button in the Variables window.
When you need to calculate the difference between two columns, you will need to do this
in a new column. Use Manage-> Formula to calculate the difference between two
columns and place the results in a new column.
The mean of trials 1-15 and the mean of trials 16-30 are done for you in columns at the
end of the file.
t-test: used to compare the means of two distributions given the between group and
within group variances
Factorial ANOVA is an extension of the t-test for >2 groups.
Analyze-> New View
Unpaired Comparisons
Unpaired t-test
Hypothesized difference: 0
95% Confidence Interval
Tail: Both
OK
Assign a continuous variable and a nominal variable with the Add button.
Paired t-test: used when multiple response variables are measured for each individual
Repeated measures ANOVA is an extension of the paired t-test for > 2 groups.
Analyze-> New View
Paired Comparisons
Paired t-test
Hypothesized difference: 0
95% Confidence Interval
Tail: Both
OK
Assign two continuous variables with the Add button.
To make your graphs, you will use Cell Plot->Point Chart to plot the two means with
95% Confidence Intervals. While the t-test tables are still selected, Point Chart will
use the same two variables already selected.
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WORM RUNNERS
In 1955 two psychologists, Thompson and McConnell, published a paper claiming that
they had successfully trained individuals of the planarian species Dugesia dorotocephala
(black planarian) with a classical conditioning task. Planarians had hardly ever been
used before in learning experiments, but the Thompson and McConnell experiment was a
relatively straightforward extension of behavioral psychology techniques to a new
organism. The subject of planarian learning did not become the subject of controversy
until after the publication of further, dramatic experiments. As mentioned above,
planarians can regenerate into viable flatworms if they are cut into pieces. McConnell
used this regenerative property to ask exciting questions about the retention of memory.
He trained worms, cut them in half, allowed them to regenerate and then tested them to
see how much of their previous training they had retained. Surprisingly, worms that
regenerated from the brainless tail sections remembered as much as if not more than head
section regenerates (McConnell et al., 1959). A further characteristic of the particular
species used by McConnell is that it is cannibalistic. In an even more daring and
controversial paper, McConnell fed pieces of trained worm to hungry untrained worms
(McConnell, 1962). Their results indicated that a behavioral tendency or a “memory” had
been transferred from the trained to the untrained worms. “Knowledge, it seemed, was
edible!” Others went on to identify the mechanism of memory transfer and focused their
efforts on RNA by injecting a recipient with intact RNA isolated from previously
conditioned worms. The training could be transferred if the RNA was first degraded
(Jacobson et al., 1966). For a time, experimenters in this field published a special-interest
newsletter titled “Worm Runner’s Digest”. The results of those studies are still
controversial. However, recent advances in our understanding of gene regulation
including additional functions of RNA molecules have renewed scientific interest in this
protocol.
PROCEDURE
In the back of the room there is a container of planarians to be used for a long-term
learning experiment (labeled “for training”). Each day these flatworms will be trained to
go right (Carey’s class) or to go left (Ned’s class).
1. Hook the 9 volt battery to the Train-a-Tray. Attach a wire between the positive
battery terminal to the + sign on the Train-a-Tray. Attach the other wire to the
Train-a-Tray only. You will manually touch the loose end to the negative terminal
of the battery in order to deliver a “punishment.”
2. Fill the Y-trough with 3 ml of pond water. Fill the pre-training holding pen with
pond water
3. Gently place your 3 worms in the pre-training holding pen using the disposable
pipette as before.
4. Get 5-6 worms from your habituation experiments and allow them to crawl
around the Train-a-Tray trough to get it good and slimy. (~5minutes)
5. Remove the slime contributors.
6. Place your first flatworm for training at the base of the Y-Maze with its head
pointing toward the Y and watch it crawl.
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7. When it reaches the Y and is between the center contact point and the contact
point in one Y arm:
a. If it goes down the wrong arm, it is punished with a quick shock. When it
stretches out to crawl again, use the disposable pipette to return it to the
“already trained” container for training tomorrow.
8. Each worm should receive 3 training trials
9. Each group of 4 students should train 3 flatworms (or more if there are < 6 student
groups in class).
10. When you are finished, return all worms to the “already trained” container for
training tomorrow.
11. Rinse your training tray. (DO NOT USE SOAP.)
ANALYSIS
Determine the number of worms making correct choices and the number of worms
making wrong choices observed by your team.
Record these in the lab data collector for today’s lab. http://collector.reed.edu/
You will enter: 1) your name
2) your partners' names
3) class (Ned/Carey)
4) day (T,W,TH,F)
5) the total # of correct choices.
6) the total # of incorrect choices.
At the end of the week, the data will be available from all classes, so that we can use lab
lecture to determine if the worms have learned. We will see if the worms made
significantly more correct choices on Friday than on Tuesday. No assigned write up other
than your lab notebook record.
References (will be available in lab if you are interested)
Thompson, R. and McConnell (1955) Classical Conditioning in the Planarian Dugesia
dorotocephala, J. Comp Phsyiol Psych 48:65-68.
McConnell, J.V., Jacobson, A.L. and Kimble, D.P. (1959) The Effects of Regeneration
upon Retention of a Conditioned Response in the Planarian. J. Comp Phys Psych 52:1-5.
McConnell, J.V. (1962) Memory Transfer Through Cannibalism in Planarians J
Neuropsychiatry 3:s42.
Jacobson, A.L. Fried, C., Horowitz, S.D. (1966) Planarians and Memory. Nature
209:599-601.
Hawkins, R.D., Tracey E. Cohen, T.E., and Kandel, E.R. (2006) Dishabituation in
Aplysia can involve either reversal of habituation or superimposed sensitization Learning
and Memeory 13:397-403.
Rankin, C.H. and Carew, T.J. (1988) Dishabituation and sensitization emerge as separate
processes during development in Aplysia. Journal of Neuroscience 8:197-211.
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Mongeluzi,D.L. and Frost, W.N. (2000) Dishabituation of the Tritonia Escape Swim
Learning and Memory 7:43-47
Appendix
Learning can be defined as a process that expresses itself as an adaptive use information
to cause a change in behavior resulting from experience. Though information can be
learned that does not lead to the change in behavior, that learning is very difficult to
detect in most animals. The stages of learning include acquisition, consolidation,
retrieval and extinction. Memory can be defined as the encoding, storage, and retrieval
(or forgetting) of information from past experiences. Memory is necessary if learning is
to take place.
Non-associative learning occurs after repeated presentation of a stimulus. In the first part
of this lab, you explore simple forms on non-associative learning, sensitization and
habituation. Habituation is fundamentally different than fatigue, the loss of efficiency
in the performance of motor act due to physiological run down. It is also different than
sensory adaptation that occurs at the level of the sensory receptor, when it simply stops
sending impulses after repeated stimulation. In habituation, the sensory cell is still
sending signals to the CNS, but they are essentially ignored.
Associative learning is a broad category that refers to many of our daily activities:
learning to be afraid, learning to talk, learning a foreign language, or learning to play the
piano. In essence, associative learning involves the formation of associations among
stimuli and /or responses. It is usually subdivided into classical conditioning and
operant conditioning. Classical Conditioning is a type of associative learning, also
known as Pavlovian conditioning. Ivan Pavlov described the learning of conditioned
behavior as being formed by pairing stimuli to condition an animal to give a certain
response. The simplest form of classical conditioning, is reminiscent of what Aristotle
would have called the law of contiguity, which states that: “When two things commonly
occur together, the appearance of one will bring the other to mind." This type of
conditioning is induced by a procedure in which a generally neutral stimulus, termed the
conditioned stimulus (CS), is paired with a stimulus that generally elicits a response,
termed the unconditioned stimulus (US). At first the unconditioned stimulus will elicit
the unconditioned response (UR). After repeated pairing of a conditioned stimulus
with the unconditioned stimulus in order to evoke the unconditioned response, the
conditioned stimulus alone will be sufficient to evoke a response that is now termed the
conditioned response (CR). Operant Conditioning is the type of associative learning
made famous by B.F. Skinner. In operant conditioning, learning occurs when an animal
performs an action in the course of normal behavior and this particular action is
reinforced (either positively or negatively). After sufficient pairing, the animal learns to
associate its action (the operant) with the reinforcement. This is the type of learning
we examine with the Train-a-Tray in the second part of lab.
For both associative and non-associative learning, the information is encoded in the
animal’s nervous system through modifications of biophysical properties of neurons, as
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well as the strength of synaptic connections among neurons. These changes are often
referred to as a “memory trace” or “engram”. In humans there is no single universal
system for learning and memory. Instead, different memory systems can use different
mechanisms, and a single memory system will include multiple mechanisms. We will
discuss these mechanisms in lecture.
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