13. FARS 2. Population coding and Working Memory (2001)
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Transcript 13. FARS 2. Population coding and Working Memory (2001)
Michael Arbib: CS564 - Brain Theory and Artificial Intelligence
University of Southern California, Fall 2001
Lecture 13.
The FARS model of Control of Reaching and Grasping 2
Reading Assignments:
FARS Model:
Fagg, A. H., and Arbib, M. A., 1998, Modeling Parietal-Premotor
Interactions in Primate Control of Grasping, Neural Networks,
11:1277-1303.
The class also reviewed material on serial order and basal ganglia
contained in the slides for Lecture 9. FARS Model 1
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Coarse Coding/Population Coding
To code some variable x lying in an interval [a,b) we
could take n cells, with cell i (i = 0, …, n-1) firing if and
only if the current value of x lies in the ith subinterval
(b a )(i 1)
(b a )i
a n , a
n
In coarse coding, we achieve much greater discrimination by taking into
account the continuously varying firing level fi of each cell, and then
we can decode values of x actually varying across each interval, using
some such formula as
ba
fi a
n 1
i 0
n 1
n 1
f
i 0
i
Note: In the Georgopoulos study we saw “negative votes” for firing
below the neuron’s resting discharge rate.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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The “Visual Front End” of the FARS Model
F4
VIP
(arm goal position)
Parietal
Cortex
(position)
How (dorsal)
(object/grasp transform)
F5
AIP
PIP
(shape, size, orientation)
(grasp type)
Visual
Cortex
IT
What (ventral)
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
3
cIPS* IT connections are hard-wired
for a simple set of objects
PI P
IT
Cyli nder
Box
Sphere
gene ra l
gene ra l
gene ra l
dia m e te r
width
dia m e te r
le ngth
le ngth
height
PI P
IT
Cyli nder
Box
Sphere
gene ra l
gene ra l
gene ra l
dia m e te r
width
dia m e te r
le ngth
le ngth
height
PI P
IT
Cyli nder
Box
Sphere
gene ra l
gene ra l
gene ra l
dia m e te r
width
dia m e te r
le ngth
le ngth
height
Note the use of coarse coding
* In the paper we spoke of PIP where we now say cIPS.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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cIPS AIP connections are hard-wired
for a simple set of affordances
PI P
Cyli nder
ge ner al
diam eter
na rrow
wide
le ngth
short
long
AIP
A
B
C
preci sion
apert ure = 20mm
preci sion
preci sion
D
preci sion
apert ure = 60mm
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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IT AIP
The mapping from object identity in IT to maps directly
to both the grasp type and the aperture of grasp in AIP
when the nature of the object implies such data:
E.g., in the case of AT, the projection from IT can provide the
necessary grasp type and parameters for a lipstick but not for a
cylinder.
IT
narrow cylinder (bottle cap)
wide cylinder (jar top)
AIP
A
B
C
precision
aperture = 20mm
precision
precision
D
A bottle cap activates
a precision grasp
with a narrow
aperture.
A jar top maps to a
precision grasp with
a wide aperture.
precision
aperture = 60mm
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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cIPS IT connections are hard-wired
for a simple set of objects
PI P
IT
Cyli nder
Box
Sphere
gene ra l
gene ra l
gene ra l
dia m e te r
width
dia m e te r
le ngth
le ngth
height
PI P
IT
Cyli nder
Box
Sphere
gene ra l
gene ra l
gene ra l
dia m e te r
width
dia m e te r
le ngth
le ngth
height
PI P
IT
Cyli nder
Box
Sphere
gene ra l
gene ra l
gene ra l
dia m e te r
width
dia m e te r
le ngth
le ngth
height
Note the use of coarse coding
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
7
F5 activity during execution of a precision grasp
The top two traces show the position of the thumb and index finger.
Left: The next five traces represent the average firing rate of five F5 neurons (set-,
extension-, flexion-, hold-, and release-related). The remaining five traces represent
the various external (Ready, Go, Go2) and internal (SII) triggering signals.
Right: Illustrating the temporally distributed coding of F5 cells.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Positioning F2, F6 and Areas 46 and SII in
Monkey
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Prefrontal Influences on F5
pre-SMA
Frontal Cortex
F6
Inferior
Premotor
Cortex
F4
(arm goal position)
46
(grasp type)
Dorsal
premotor
cortex
F5
F2
(abstract
stimuli)
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Grasp Selection in F5
Within F5, the active grasps compete through a
winner-take-all
Area 46, working in conjunction with F6, supplies task-dependent
biases for grasp selection in F5, based upon
task requirements (such as what is going to be done after the
grasp), or
a working memory of a recently executed grasp.
The biasing can
be on the class of grasp (e.g. power versus precision), or
include the parameters of the grasp (e.g. width of aperture)
mechanism which incorporates any biases that might be received
from area 46.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Supplementary Motor Area (SMA) in Monkey
a
unilateral lesion of the SMA disrupts the monkey's
ability to allocate his hands to different subtasks
of a bimanual task (Brinkman, 1984)
SMA is involved in the temporal organization of complex movements
(Tanji, 1994).
Luppino, Matelli, Camarda, & Rizzolatti subdivide SMA:
SMA-proper (F3; the caudal region) has heavy projections to the
limb regions of F1 and related portions of the spinal cord.
F6 (pre-SMA) does not project to the spinal cord, and has only
moderate projections to areas F3 and F2 (the dorsal premotor cortex),
but has a very heavy projection to area F5.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Pre-SMA
pre-SMA
F6
Inferior
Premotor
Cortex
F4
(arm goal position)
Frontal
Cortex
46
Dorsal
premotor
cortex
(grasp type) F5
F2
(abstract
stimuli)
F6 (pre-SMA) has a very heavy projection to area F5.
Inputs into area F6 include VIP, and area 46.
F6 contains neurons that become active when an object that the monkey is
about to grasp moves from being out of reach into the peripersonal space of
the monkey
Interpretation: this class of pre-SMA (F6) neuron is responsible for
generating a go signal when it is appropriate for the monkey to begin a
reaching movement.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Area 46
Area 46 has been implicated as a working memory
in tasks requiring information to be held during
a delay period (Quintana & Fuster, 1993).
This memory has been posited to participate in learning tasks involving
complex sequences of movements (Dominey, 1995).
Area 46 projects to F6, and also exchanges connections with area F5
(Luppino, et al., 1990; Matelli, 1994).
When a human is asked to imagine herself grasping an object, activated
areas (PET or fMRI) involved include:
Area 46 (Decety, Perani, Jeannerod, Bettinardi, Tadary, Woods, 1994)
Area 44 (a possible F5 homologue)
A site along the intra-parietal sulcus (Grafton, et al., 1996).
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Role of Area 46 for Grasping in the Dark
pre-SMA
F6
Inferior
Premotor
Cortex
F4
(arm goal position)
Frontal
Cortex
46
Dorsal
premotor
cortex
(grasp type) F5
F2
(abstract
stimuli)
During the performance of the task in the light, area 46 maintains a memory of
those F5 cells that participate in the grasp.
To simulate performance in the dark, PIP and IT are then cleared.
If a new trial is initiated soon enough, area 46 provides positive support to those
F5 cells that were active during the first trial.
The area 46 working memory provides a static description of the grasp that was
recently executed, in the sense that the temporal aspects of the grasp are not
stored - only a memory of those units that were active at some time during the
execution.
[Area 46 is involved in human imagination of grasp execution.]
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Conditional Tasks and Area F2
pre-SMA
F6
F4
(arm goal position)
46
(grasp type) F5
Dorsal
premotor
cortex
In addition to
simulating the Sakata
task, we simulate
conditional tasks.
F2
(abstract
stimuli)
Dorsal premotor cortex (F2) is thought to be responsible for the association of
arbitrary stimuli (an IS) with the preparation of motor programs (Evarts, et al.,
1984; Kurata & Wise, 1988; Mitz, Godshalk, & Wise, 1991; Wise & Mauritz, 1985).
In a task in which a monkey must respond to the display of a pattern with a particular
movement of a joystick:
some F2 neurons respond to the sensory-specific qualities of the input. However,
many F2 units respond in a way that is more related to the motor set that must be
prepared in response to the stimulus.
When a muscimol lesion in this region is induced, the monkey loses the ability to
correctly make the arbitrary association.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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F5 activity during execution of a precision grasp
The top two traces show the position of the thumb and index finger.
Left: The next five traces represent the average firing rate of five F5 neurons (set-,
extension-, flexion-, hold-, and release-related). The remaining five traces represent
the various external (Ready, Go, Go2) and internal (SII) triggering signals.
Right: Illustrating the temporally distributed coding of F5 cells.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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The Complete FARS Model
Inferi or
Premotor
Cortex
F6
F4
VIP
(arm goal position)
Parietal
Cortex
(position)
How (dorsal)
(object/grasp transform)
46
(grasp type)
AIP
F5
PIP
(shape, size, or ientation)
Vis ual
Cortex
F2
(abstr act
stimuli)
IT
What (ventral)
expect at ion
(sensory
hyperf eat ures)
A7
(inter nal model)
SII
MI
(muscle assemblies)
SI
motor commands
(elem entar y
sensory
features)
sensory info
hand
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Thumb and index finger temporal behavior as a
function of cylinder size
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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F5 cell responses during precision grasps of seven
different apertures
This particular cell is
active only for narrow
precision pinches
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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F5 movement-related cell (A) and a hold-related
(B) cell during the perturbation experiment
20mm/30mm traces correspond
to presentation and grasping
of a 20mm and a 30mm
cylinder, respectively;
traces labeled 2030 and 30
20 indicate perturbation
trials, in which a 20mm
cylinder is switched for a
30mm cylinder, and a 30mm
cylinder for a 20mm one,
respectively.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Two objects that map to the identical grasp
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Comparison of population
responses towards two
different objects (but
identical grasps).
Lighted movement task, AIP
(A) and F5 (B) cells; and
AIP populations during
fixation (C) and dark
movement (D) tasks.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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F5 Feedback to AIP
Visual-related
AIP receive object-specific inputs; motor-related cells
receive recurrent inputs from F5, which do not demonstrate object-specific
activity.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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A single object mapping to two possible grasps
Before execution, one grasp must be selected based upon the current
context (e.g., based upon an Instruction Stimulus).
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Two F5 units (A, B) in
response to the four
conditions: (c,pr), (c,pw),
(nc,pr), and (nc,pw). c =
conditional; nc = nonconditional; pr = precision
pinch; pw = power grasp.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Four boxes of different dimensions
Grasping is performed
along the horizontal axis.
The two blocks in the left
column are grasped using
a precision pinch of a
10mm aperture; the blocks
on the right require a
20mm aperture.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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Comparison of AIP visual
responses for objects of the
same (A) and different (B)
widths; and AIP motorrelated responses (dark
movement condition) for
objects of same (C) and
different (D) widths.
Michael Arbib CS564 - Brain Theory and Artificial Intelligence, USC, Fall 2001. Lecture 13. FARS 2
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