Ingen bildrubrik

1
The Rat's Tactile Discriminative Abilities
By Filip Aggestam Dr. Peter Cahusac
Introduction The mystacial vibrissae represent a
sensitive tactile system that is an essential
tool for the rat to perceive its immediate
environment. The rat, as a nocturnal animal with
notoriously bad vision, depends at times
exclusively on its whiskers to guide its
movements through familiar territory (Jenkinson
and Glickstein, 2000). The vibrissae are
discrete tactile sensors that project out from
each side of the animals face. According to
Brecht et als (1997) terminology the
macrovibrissae are long and project out
laterally in a pattern of five rows, each row
containing up to seven vibrissae, and
microvibrissae situated frontally that are more
numerous and shorter (see Fig. 1).
Taken from Brecht et al (1999)
Figure 1. The Lashley Jumping stand and the
mystacial vibrissae.

• The mystacial vibrissae are essential for
• Depth perception (Schiffman et al. 1970).
• Analyse Surface Features(Simons Carvell, 1990)
• Defence mechanism (Blanchard et al. 1994)
• Gap crossing (Jenkinson and Glickstein. 2000)

The prevalent view in regard to the function of
the mystacial whiskers has been as a skin like
receptive surface. It has been suggested that the
rats vibrissal apparatus is almost as sensitive
as human fingertips. Simons and Carvell (1990)
clearly demonstrated the sensitivity of the
mystacial vibrissae with trained rats performing
a fine-grained texture discrimination Generally,
research efforts up to now have lead to the
opinion that the mystacial vibrissae comprise a
sensory system that simply expands the rats
awareness of its immediate surroundings, like an
extended skin-surface (Vincent, 1912 Guic-Robles
et al. 1989).
Figure 2. The stimuli and rat performing a
discrimination.

• The mystacial vibrissae are an essential
  component to perceive and react to a wide range
  of stimuli in their surrounding milieu. Given the
  nature of the rats normal habitat it might be
  expected that discriminating between natural
  objects, such as wood and stone would be
  important. Previous research has already
  established that the rat can detect many surface
  features, such as roughness (Simons Carvell),
  form (Washington Cahusac, 1993), and size
  (Krupa et al 2001). It would be of interest to
  investigate whether the rat would be able to
  extract information about the hardness of a
  stimulus.
• Aim of the study
• This study investigated the rats ability to
  discriminate between different materials using
  only hardness as a cue.
• The wind represents a natural element of any
  environment, hence the influence of wind on
  performance during a roughness discrimination was
  investigated.
• Finally, it was of interest to investigate the
  possibility of the rat using auditory cues to
  reveal the hardness of a stimulus when whisking.

2
The Rat's Tactile Discriminative Abilities

• Summary of Results
• Reliably able to discriminate between Stone,
  Metal, Wood and Plastic using only hardness as a
  cue.
• Materials with similar hardness and surface
  properties, such as the 4 different metals, could
  not be discriminated.
• Auditory cues are not used during discrimination
  since white noise does not effect performance.
• Wind levels of approximately 7-9 m/s inhibit the
  rat from performing a whisker discrimination.

Subjects
Sixteen male Wistar rats were obtained for this
study. Having initial weights between 135-175
gram. Due to limitations in time all rats did not
reach the designated performance criterion, this
resulted in that six rats had to be discontinued.
Materials and Apparatus A Lashley Jumping
Stand was employed to train the rat to perform a
roughness discrimination. The proportions of the
apparatus are 100cm x 80cm. It consists of three
elevated platforms, a start platform and two
choice reward platforms. The distance between
the start platform and the choice platforms could
be adjusted according to the size of the rat. On
each choice platform a gate lead into a hidden
platform with a food cup (see Fig. 3). Eight to
teen standard food pellets were given as a daily
food ration. A reward was given consisting of
Maryland cookies. During the course of the
experiment a black spray paint, clove oil were
used on the stimuli. A small torch pen was used
when working in complete darkness. A White-noise
generator, type 419C (Serial Number 5211, Dawe
Instruments Ltd) with an amplifier and speakers
were used. Furthermore an electrical fan (Carlton
Breezy fan, 40 cm Pedestal fan, 230-240v50Hz)
was employed.
Training Procedure 6 weeks were invested into
training a rat to perform a roughness
discrimination using only their whiskers, finding
a reliable reward and getting the rat used to the
experimenter. The lack of motivation presented a
problem, this was dealt with by applying a
deprivation schedule. The schedule consisted of
giving the rats nine pellets of food at the end
of each session. During the weekend when no
testing occurred the rats were given ad libitum
access to food and water. The texture
discrimination training consisted of a procedure
in which the rat had to choose between a rough or
smooth stimulus. The rat received a reward when
choosing the rough stimulus. The same procedure
was implemented on all rats and experiments, its
purpose was simply to learn the rat that it had
to make a choice of either stimuli using only
their whiskers. A single trial proceeded as
following, the rat was placed on the start
platform and had 30s to make its choice, if they
failed to do so within this timeframe they were
put back into their cage for 90s. If the subject
made an incorrect choice they were also put back
into their cage. A correct choice resulted in 30s
access to the food tray (see Fig. 4). To prevent
the influence of any visual cues during the
discrimination task all trials were simply
conducted in complete darkness. A pen torch was
used between trials to guide the experimenter and
to take down the results. To prevent the animal
from using olfactory cues all the stimuli were
cleaned and covered with clove oil after each
experimental session. Initially the behaviour of
16 rats were tested over 5 week in daily sessions
(5/7 per week), 15 trials per day. After the
training period 10 rats were tested in the same
manner but with 25 trials per day . The
predetermined performance criterion was set as a
95 confidence interval over more than two days,
the subjects reached this when they had 75
correct on all trials over a full days session.
Hardness discrimination test The exact same
procedure was followed except that the 10
remaining rat were divided into 5 groups with 2
rats in each. Each pair was introduced to 2
stimuli consisting of four different materials,
e.g. wood and stone or plastic and metal, etc. 4
Metals were used later (Iron, Aluminium, Copper
Brass) in a second discrimination test. Exposure
to the new materials was continued until the rats
were reliably able to discriminate between them,
this took approximately 2 weeks. White noise
test Once again the same procedure except that
the rats where now also exposed to a white noise
generator to see whether this would have any
effect on the rats performance (see Fig 5.) This
experiment took only 2 days since the rats had
already reached their performance criterion. The
behaviour of 4 rats were tested over 2 days, 15
trials per day. Wind strength test This last
test also followed the same procedure but with a
fan installed on top of the apparatus to test
what wind velocity would disrupt the rats
performance. This experiment took only 2 days
since the rats had already reached their
performance criterion. The behaviour of 6 rats
were tested over 2 days, 15 trials per day.
Figure 3. The Lashley Jumping stand

• What are the results?
• A rat required approximately 2 weeks of training
  to reliably discriminate between a simple rough
  and smooth stimulus and reach the predetermined
  performance criterion.
• White noise was presented over 2 days. It did not
  significantly influence the performance (see Fig.
  5).
• It took 2 weeks for a rat to learn how to
  discriminate between materials with different
  hardness (stone, metal, wood plastic). However,
  the rats were unable to discriminate between
  different metals (see Fig. 5)
• Wind was introduced as a influence during
  whisking. It was found that wind velocities of 7
  to 9 m/s significantly disrupted the rats ability
  to perform a discrimination.

Figure 4. A rat whisking a stimulus and gaining
access to a reward.
3
The Rat's Tactile Discriminative Abilities

• Conclusions
• So what can be said about the rats mystacial
  vibrissae? Previous studies have confirmed that
  the vibrissal array may provide a wide range of
  information about objects. The rodents whiskers
  operate in a very flexible manner allowing the
  rat a fairly high-resolution perception of novel
  objects or environments. It can be concluded that
  the facial whiskers enable the rat to derive an
  impressive amount of information from its
  environment, which makes it a very useful tool
  for survival in the wild.
• The object of this study was to investigate
  whether the rat would be able to discriminate
  between different materials using only hardness
  as a cue. When presenting the rats with materials
  that are very different in terms of hardness,
  such as wood and stone, it does appear as if the
  rats are able to successfully discriminate
  between them. There are however limitations in
  their ability to detect hardness, an attempt was
  made to see whether the rat would be able to tell
  different metals apart, in this case aluminium,
  bras,copper iron. It seems as if the rat is not
  capable to discriminate between materials when
  the range of hardness is more limited.

• Potential Problems...
• The Clove oil might not completely block out
  olfactory cues
• Alternative cues might influence the rats
  choice, e.g. friction
• Novelty of the wind and white noise might have
  influenced the results
• Shortage of time for the wind and white noise
  experiment limit the possibility for a conclusion
• Future research...
• Investigate the effectiveness of clove oil
• Use stimuli with measurable hardness to more
  closely investigate the limits.

Figure 6. Rat whisking a stimuli and crossing
the gap.

• Conclusion continued
• We also investigated the effect white noise would
  have on performance, the purpose of this
  experiment was mainly to test if the rat were
  using auditory cues when whisking a stimulus.
  Introducing white noise did however only decrease
  the performance slightly, this reduction in
  performance was probably only due to the novelty
  of the white noise generator.
• Finally, we looked at the effect wind would have
  on the performance of a whisking rat. Introducing
  a fan on top of the apparatus that could generate
  different levels of wind velocity. The results
  indicate that the rat is able to continue
  discriminating between stimuli until a wind
  velocity of approximatelly 7-9 m/s

Acknowledgments I would like to thank Dr. Peter
Cahusac, the Nuffield Foundation and the
University of Stirling for making this project
possible.
Figure 7. The White noise generator and fan.