Octopus' Out Of Water

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Octopus' Out Of Water Reaching Movements
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Abstract

• Octopus vulgaris has been studied for more than
  50 years, but it has proven to be a very
  complicated creature.
• The research group focus is understanding the way
  the octopus moves, so this knowledge will be
  used, for example, in the field of robotics.
• It has been discovered that the octopus has a
  stereotypical reaching movement.
• The goal was to understand the mechanisms that
  generate those movements and create a dynamic
  computer model.

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Octopus

• Belongs to the Cephalopoda. The only one with a
  brain.
• An octopus is composed mainly of muscles.
• Arms uses sensing, chemotaxis, movement,
  catching pray There is no preferred arm.
• Special abilities change color, change body
  texture, jet propulsion, ink ejection,
  regenerate.
• Octopus is muscular hydrostat.

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Degrees of freedom

• Degree of freedom - The relative movement between
  two parts that can be describes with one
  parameter.
• Skeleton imposes a constraint on the number of
  degrees of freedom.
• The human hand has 7 degrees of freedom.
• The octopus has a virtually infinite number of
  degrees of freedom.

How can a movement be calculated?!?!
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Reaching movement

• It was found (Guetfruind et al. 1996) that the
  octopus has a stereotypical active reaching
  movement (not whip like).
• It can be described as such a. A bend is formed
  somewhere along the arm (suckers towards
  target).b. The bend propagates from the
  base part of the arm to its tip. The part
  of the arm proximal to the bend remains
  extended.

a. Bend formation
b.Bend propogation
(Gutfreund et al. 1996)
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Reaching movement

• The bend of a normal reaching movement advances
  in a slightly curved manner in a single linear
  plane.

(Gutfreund et al. 1996)
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Velocity profile

• Tangential velocity- bend advance in x,y,z axis
  (in 3D).
• The velocity profile of the octopus has bell
  shaped characteristics

Velocity stats
16 cm/sc min
61 cm/sc max
35 cm/sc mean
9.5 cm/sc sd
(Gutfreund et al. 1996)
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Embedded Reaching movement

• The total number of neurons in an octopus is
  .
• In the arms, there are neurons.
• There are motor neurons in each arm.
• This information led to the assumption that the
  reaching movement of the octopus is embedded in
  the arm itself.

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Evoked Reaching movement
Arm extensions can be elicited in denervated
arms by electrical stimulation of the arm axial
nerve cord or by tactile stimulation of the skin
or suckers, suggesting that a major part of
this voluntary movement is controlled by a motor
program that is confined to the arms
neuromuscular system. (Sumbre et al. 2001)
a. Arm cross section
b. Axial nerve cord
(Sumbre et al. 2001)
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The Reaching Model

• Our group has devised a dynamic computer model to
  simulate the reaching movement of the octopus in
  2D (3D is now the goal).
• The model has a similar velocity profile like the
  normal reaching movement.
• There are several parameters that can be changed
  gravity, friction in water (drag), activation
  force

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OOW Movement Goals

• Analyze differences In Water and OOW environments
  for the octopus, and its implications.
• Characterizing the bend point position in space,
  velocity profile, duration.
• Understand the mechanism behind the reaching
  movement in general.
• Comparison to the Reaching Dynamic Model.

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OOW- Methods

• The octopuss movements were videotaped on two
  cameras.
• For each experiment a calibration body was used,
  in order to integrate the data from the two
  cameras into three dimensions.
• During the OOW experiment, one of the octopuss
  arms was held by the experimenter.

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OOW Environment

• In OOW environment some parameters are not the
  same as in water
• No drag force OOW.
• No buoyancy. Buoyancy force (Density) (Volume)
• Gravitation force.
• OOW movement is probably energetically costly.

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OOW Bend pos. in Space

• The bend position in space in normal reaching
  movement is in a single linear plane, with
  slightly curved path.
• The bend position in OOW reaching movement is in
  three dimension.

Movement 6_1
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OOW Velocity profile

• Velocity profile for normal reaching was
  calculated using Tangential velocity
  formula.BUT,The nonlinear nature of the OOW
  reaching movement makes this formula inadequate.
  Another was used
• (which I term Euclidian velocity)
• Reaching movement Velocity profile table

OOW 2 OOW 1 Upwards Normal
15.945.5 7.882.59 28.110.74 35.249.55 Mean peak vel. (cm/sec)
13 23 17 83 num of movements
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OOW movement duration

• Reaching movement duration table

OOW 2 OOW 1 Upwards Normal
1.030.34 0.970.4 1.110.38 1.020.42 Mean dur. (sec)
13 23 17 83 num of movements
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Correction of arm base during OOW reaching
movement- two mechanisms
90 view of the bend point as a function of time
base
base
Tan vel.
Euc vel.
The advance of the bend point is independant of
the base correction
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Bell shaped velocity profile?

• When using the Euclidian velocity profile on
  normal reaching movements, the first phase was
  gone.
• This implies that this phase is due to a
  correction of the base of the arm.

Euc vel profile
(Tan-Euc) vel profile
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OOW The Model

• The parameters of the model were modified1. The
  octopuss arm base is directed upwards.2. The
  Drag force is eliminated.3. No buoyancy OOW.
• The activation forces were modified on need.

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Fetch movement

• It is interesting to see another kind of
  movement-the fetch movement, and understand how
  this movement can be generated.

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Fin!
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In water reach (no gravity)
OOW reach (gravity)
OOW In water
0.72 sec 0.8 sec Movement dur.
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Circadian Rhythms
Amit Shabtay 2004
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The Clock in our Lives

• In 1729, DeMarain described a daily rhythmic
  opening and closing of the leaves of a heliotrope
  plant.
• What was very interesting, is that this rhythm
  persisted, even in the absence of light.
• Since then it has been discovered that this
  clock is present in almost all eukaryotic life.
• Another kind of clock was found- a timer, on
  which we will not elaborate.

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Definitions

• Free run- only darkness conditions.
• Circadian time- the inner cycle of the animal,
  which is usualy ! 24 hours cycle.
• Solar time- 24 hours cycle of the sun.
• Citegeber time- artificial cycle given to the
  animal.
• All these cycles are normalized to 24 hours cycle.

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Experimental Data
Solar time
Free run
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Reseting the Clock
What about blind people?
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There are Many Clocks

• The signal from the SCN travels to the entire
  body, and affects many functions of it.

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Phase Response Curve
Next night will be earlier
Next night will be postponed
There is a delay in the response of the clock
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Two oscillating proteins
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Control mechanism in Closed systems
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A few Words about Skeletal muscles
A skeletal muscle is a muscle that is connected
to the skeleton (as opposed to the heart muscle
or smooth muscle)
Always work in maximum tension
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Length-Tension curves
The skeletal muscle has two kinds of forces-
passive force and active force
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The Importance of Closed circle Control
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Adding Load
Load is added,Spindle is stretched
a Motoneurons cause the muscle to
contract.Spindle is relaxed
Spindle is stretched again.
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Two Variable Equation
Muscle length as a function of firing motoneurons
Firing motoneurons as a function of muscle length
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Two Variable Equation
Matching axes
Muscle length as a function of firing motoneurons
Firing motoneurons as a function of muscle length
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Two Variable Equation
Joining graphs
Working point
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Correcting Errors
Correction
Error
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Correcting Errors
Time of error
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Correcting Errors
When the amplification is too high, oscillations
can occur
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Stable Feedback System

• The feedback system will always be stable if
  these three conditions are met
• 1. Amplification lt 1
• 2. Short delays
• 3. Slow response to
  changes

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Returning to Working Point
Short delays, Fast response
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Returning to Working Point
Short delays, Slow response
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End