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Sequential and multilimb movements

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Title: Sequential and multilimb movements


1
(No Transcript)
2
Sequential and multi-limb movements
  • Learning objective
  • To understand and describe
  • Neural control of sequential movements PMA and
    SMA
  • Characteristics and neural control of bimanual
    movements
  • Characteristics of coordinating the eyes, head,
    and arms

3
Sequential movements
Sequential movements refer to rapid serial
actions in tasks such as typing and piano
playing. How can very rapid responses be linked
when moment-to-moment feedback is not available
(known as the serial order problem)? RT for a
single key press (simple movement) 150-200
ms RT between key presses can be lt 150
ms Answer A general motor program with the
performer monitoring overall performance to
prevent drift.
4
Neural control of sequential movements
The supplementary motor area (SMA) is involved in
learning and retrieving movement sequences (for
all body parts).
SMA
M1
pre-SMA
SMA projects to M1. Pre-SMA (front of the SMA)
projects to SMA. Strong connections between SMAs
of each hemisphere
PMA
5
PMA Sequential movements
  • Involved in sequencing motor synergies using
    sensory cues
  • receives multisensory inputs
  • large devotion to visual signals used to guide
    eye, head, body movement

6
SMA Sequential movements
Same sequencing role but based more on internal
than on external sensory cues Associated with
bimanual control
7
SMA Sequential movements
Damage to SMA results in a failure to initiate
actions without sensory cues
Monkeys trained to lift hand for
reward. Following SMA/pre-SMA lesions, massive
decline in rate of lifting Could still produce
the move-ment in response to a visual cue (food
placed at the same position)
8
SMA Sequential movements
The supplementary motor area (SMA) is involved in
learning and retrieving movement sequences (for
all body parts).
SMA
SMA projects to M1. Pre-SMA (front of the SMA)
projects to SMA. Strong connections between SMAs
of each hemisphere
M1
pre-SMA
9
Role of pre-SMA in sequential movements
Pre-SMA is involved in acquiring new sequences.
More activity when the sequence is new, compared
to when its been already learned.
New seq.
Learned seq.
10
Role of SMA in sequential movements
In contrast, SMA neurons are more active when
performing a sequence already learned than one
still being learned. Suggests that SMA may be
more involved in retrieving the sequence.
New
Learned
11
Role of SMA in sequential movements
Surprisingly, neural activity in various motor
related areas are diminished in expert sequence
players. Study comparing professional pianists
(P) and control subjects (C) on complex finger
movement tasks. Same brain areas are active, but
much less so. Perhaps the neural correlate of
effort/skill level.
C
SMA
PMA
M1
PPC
P
12
Role of SMA in sequential movements
SMA is involved in internally generated
move-ments (deciding when and what movement to
make without an outside stimulus to guide you).
SMA neurons tend to be more active for memory
guided sequences than visually-guided ones.
Visually-guided
Memory-guided
13
Role of other motor cortex areas
In contrast, PMA neurons tend to be more active
in visually-guided sequences than during
memory-guided ones.
Visually-guided
Memory-guided
14
Role of other motor cortex areas
Neural activity in M1 was similar regardless
whether movement is visual or memory guided.
Visually-guided
Memory-guided
15
Neural control of sequential movements
SMA is active when subjects imagine themselves
performing the movement sequences (mental
rehearsal), but not for simple movements.
Simple movement
Imagined sequence
Sequence of movements
SMA
M1
S1
Inferior Prefrontal cortex
SMA PFC activity is bilateral
16
Role of SMA in sequential movements
SMA neurons are more active when the task
requires the arrangement of multiple movements in
the correct sequence and correct temporal order.
For example, some SMA neurons prefer a specific
order of movements to be performed.
17
Role of SMA in sequential movements
Other SMA neurons fire more for the preparation
of a specific rank-order.
This neuron fired more when the monkey was
preparing to initiate the third movement,
irrespective of the sequence of the three
movements.
18
Role of other cortical and subcortical areas
For internally guided movements
PPC
Pre-frontal cortex
Information related to internal goals
motivational states.
Cerebellum
Basal ganglia
19
Role of other cortical and subcortical areas
For externally guided movements
PPC
Cerebellum
Parietal cortex
PMA
Pre-frontal cortex
M1
Information from vision, audition, touch etc.
Cerebellum
Basal ganglia
20
Bimanual movements
Beyond single reaches, must also coordinate the
two arms for simultaneous performance. But the
two arms may have different movements parameters
assigned. Does motion of the two arms affect
their kinematics?
21
Bimanual movements
When movements are in phase, reaction times (RT)
and movement times (MT) for the two arms are
similar to that for one arm movement.
When comparing movement parameters of the two
arms find similar time to peak acceleration,
shape of trajectory, etc. for the two hands.
22
Interference in bimanual movements
But the limb that moves to a more difficult
target (either farther away or behind an
obstacle) influences the motion of the other limb.
RT and MT for the easier (shorter) movement is
longer when accompanied by a movement to a more
difficult (longer) hand movements.
23
Interference in bimanual movements
When both hands move to
  • near/easy targets short RT
  • far/difficult targets longer RT

Reaction Times (ms)
But when one hand moves to easy target while the
other moves to more difficult target RT are
even longer for both hands.
24
Interference in bimanual movements
Accuracy also gets worse for the easier hand
movement when accompanied with a more difficult
one.
25
Symmetry of bimanual movements
Natural coordination of the arms people prefer
to move their arms in spatial-temporal
symmetry. Can be very difficult to produce
simultaneous, but spatially or temporally
asymmetric hand move-ments. e.g., try drawing
circle in frontal plane with right hand and one
in the horizontal plane with left hand. This
difficulty in coordinating asymmetric move-ments
may suggest a limitation in the control systems
ability to do these movements independently.
26
Symmetry of bimanual movements
The preference for symmetry in bimanual
coordina-tion is perceptual. Untrained
individuals are unable to produce non-harmonic
polyrhythms. But with altered feedback (gear)
they are able to
generate symmetrical movement of the flags and
non-symmetrical movements of the hands.
27
Neural control of bimanual movements
Both SMA and M1 are involved in coordinating
bimanual movements. Most M1 neurons responded
during bimanual arm movements more so than to
single arm move-ments (but almost no difference
in M1 activity for dual and single finger
movements).
28
Neural control of bimanual movements
SMA neurons responded much more during bimanual
movements than during movements of either hand.
29
Eye-head-hand coordination
The brain must synchronize the activity of two
(or more) different motor systems whose effectors
are physically separated, and have different
kinematics and dynamics.
30
Eye-head-hand coordination
People first saccade to a the target just prior
to the hand arriving there. Start times of the
eyes and hand are highly correlated, although RT
of the hand movement onset is about 200 ms longer
than that of the eyes.
31
Eye-head-hand coordination
Although hand onset is later than saccade onset,
muscle activity of the arm begins slightly before
eye movement is initiated. This suggests that
commands to the eyes and arm may be delivered
simultaneously.
32
Eye-head-hand coordination
Saccades move faster (higher peak velocity
shorter duration) when accompanied by hand
movement to the same spot.
33
Eye-head-hand coordination
Moving the eyes to the target can increase
accuracy of reach movement, even if the target is
not seen after the saccade. Eye can track unseen
hand Oculomotor and manual control systems share
spatial information.
34
Eye-head-hand coordination
Mechanism for coordinating the two systems may be
a predictive controller with an internal model of
the two systems. This would account for
increased accuracy in tracking with our eyes
(smooth pursuit) a target moving with our hand
compared to a target moving on its own.
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