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A neural test bed for simulating executive control deficits in saccade generation
Uday JagadisanNeeraj GandhiUniversity of Pittsburgh
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Typical oculomotor behaviour displays an alternating pattern of gaze shifts and fixations
Balanced exchange of activity in the brain between inhibitory networks that maintain fixation and excitatory networks that generate gaze shifts
Balance shift towards increased inhibition difficulty or delay in initiating movements
Balance shift towards increased excitation lack of movement suppression (behaviour as seen in disorders such as ADHD, Schizophrenia)
Sensorimotor function – a balance hypothesis
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Model - Reciprocal inhibition in the superior colliculus (SC)
(illustration from Munoz & Fecteau, 2002)
C
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Biasing the rostro-caudal balance in SC Objective: Perturb the balance between rostral SC and caudal SC on a trial-by-trial
basis while recording activity in both networks cannot use microstimulation (difficult to stimulate and record in the same place) cannot use inactivation (recovery over long time-scales)
Can we use the blink reflex to our advantage? Omnipause neurons (OPNs) in the PPRF have been shown to shut off during blinks,
linked to loopy eye movement associated with blink
Like the OPNs, cells in the rostral SC show a reduction in activity related to saccades – can they also be turned off using blinks?
If so, what are the consequences of this on the caudal network?
Schultz, et al. (2010)
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Single units in rostral and caudal SC (intermediate layers) of monkey (macaca mulatta)
Delayed saccade (overlap 500-1200 ms) paradigm Air-puff delivered at random time on ~25% of trials; analysis focuses on
blinks during initial fixation (Fixation Blinks) Saccade target – IN or OUT of response field
caudal
rostral
SC
Experimental Methods
TIME (ms)
Target
Fixation Point
Eye
Air-puffEye lid
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Single units in rostral and caudal SC (intermediate layers) of monkey (macaca mulatta)
Delayed saccade (overlap 500-1200 ms) paradigm Air-puff delivered at random time on ~25% of trials; analysis focuses on
blinks during initial fixation (Fixation Blinks) Saccade target – IN or OUT of response field
Experimental Methods
TIME (ms)
Target
Fixation Point
Eye
Air-puffEye lid
For more on these trials, please visit my poster on Monday afternoon (QQ13 489.01)
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Activity in the rostral SC – control vs fixation blink
-400 0 1000
25
50
75
100
Time from blink onset (ms)
Activ
ity (s
pikes
/s)
ControlFixation Blink
5 deg
-400 -200 0Time from saccade onset (ms)
Start of blink
End of blink
n = 449Suppression lasts past the blink into the delay period …
… even as the eyes are stable.
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Activity in the rostral SC – Summary (4 neurons)
Significant
1 2 3 40
20
40
60
0
20
40
60
1 2 3 4Cell Number
Activ
ity (s
pike
s/s)
Delayperiod During saccade
-500 0 7000
25
50
75
100
Time from target onset (ms)
Activ
ity (s
pike
s/s)
-400 -200 00
25
50
75
100
Activ
ity (s
pikes
/s)
Time from saccade onset (ms)
p < 0.0001 p > 0.05ControlFixation Blink
C
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Activity in the rostral SC – Summary (4 neurons)
Significant
1 2 3 40
20
40
60
0
20
40
60
1 2 3 4Cell Number
Activ
ity (s
pike
s/s)
Delayperiod During saccade
-500 0 7000
25
50
75
100
Time from target onset (ms)
Activ
ity (s
pike
s/s)
-400 -200 00
25
50
75
100
Activ
ity (s
pikes
/s)
Time from saccade onset (ms)
p < 0.0001 p > 0.05ControlFixation Blink
C
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-100 0 100 200 7000
100
200
300
400
500 ControlFixation Blink
n = 440n = 75
Time from target onset (ms)
Activ
ity (s
pikes
/s)
Increased activity in the visual response
Activity in the caudal SC – visual and delay activity
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Activity in the caudal SC – visual and delay activity Control
Fixation Blinkn = 540n = 73
-100 0 100 200 7000
100
200
Time from target onset (ms)
ControlFixation Blink
n = 440n = 75
-100 0 100 200 7000
100
200
300
400
500
Time from target onset (ms)
Activ
ity (s
pike
s/s)
-100 0 100 200 7000
40
80
120
ControlFixation Blink
n = 168n = 42
Time from target onset (ms)
Activ
ity (s
pike
s/s)
Activ
ity (s
pike
s/s)
-100 0 100 200 7000
100
200
300
ControlFixation Blink
n = 307n = 7
Time from tar
Periods of increased activity
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Activity in the caudal SC – saccade-related burst
-500 -100 0 100 300
500
400
300
200
100
0
Time from saccade onset (ms)
Activ
ity (s
pike
s/s)
ControlFixation Blink
n = 540n = 73
-500 -100 0 100 3000
100
200
300
400
500
600
700 ControlFixation Blink
n = 440n = 75
Time from saccade onset (ms)
Activ
ity (s
pike
s/s)
-500 -100 0 100 3000
100
200
300
400
500
600 ControlFixation Blink
n = 307n = 7
Time from saccade onset (ms)
Activ
ity (s
pike
s/s)
-500 -100 0 100 3000
50
100
150
200
250
300 ControlFixation Blink
n = 168n = 42
Time from saccade onset (ms)
Activ
ity (s
pi
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Activity in the caudal SC – Summary (17 neurons, 2 monkeys)
0 100200 700Time from target onset (ms)
Activity incontrol trials
-500 -100 0 100 300Time from saccade onset (ms)
0 200 400 6000
200
400
600
10 10010
100
500
500(log-log)
Activity incontrol trials
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0 100200 700Time from target onset (ms)
Activity incontrol trials
-500 -100 0 100 300Time from saccade onset (ms)
0 200 400 6000
200
400
600
10 10010
100
500
500(log-log)
Activity incontrol trials
Activity in the caudal SC – Summary (17 neurons, 2 monkeys)
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0 200 500 1000 0 200 500
0.15
0.1
0.05
0
0.05
0.1
0.15
Time from target onset (ms)
Propo
rtion
of tr
ials i
n eac
h bin
Time from GO cue (ms)
ControlFixation blink -correctFixation blink - early
0
Behaviour – early (delay period) saccades
Story so far ...
What happens on these trials?
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-100 0 100 200 300 400 500 600 7000
100
200
300
400
Time from target onset (ms)
Activ
ity (
spik
es/s)
ControlFixation Blink -correct
-100 0 100 200 300 400 500 600 7000
100
200
300
400
500
600
700
Time from target onset (ms)
Activ
ity (
spik
es/s)
ControlFixation Blink - correct
Increased excitability associated with early saccades
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-100 0 100 200 300 400 500 600 7000
100
200
300
400
Time from target onset (ms)
Activ
ity (
spik
es/s)
ControlFixation Blink -correctFixation Blink - early
-100 0 100 200 300 400 500 600 7000
100
200
300
400
500
600
700
Time from target onset (ms)
Activ
ity (
spik
es/s)
ControlFixation Blink - correctFixation Blink - early
Increased excitability associated with early saccades
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Blinks during fixation lead to reduced fixation network activity that persists for several hundred milliseconds even as the eye position is stable
The reduction of fixation network activity in the rostral SC may be related to the increased excitability in the response of neurons in caudal SC
We have established a model that can be used to study the balance between excitation and inhibition in the saccadic system
Summary
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Acknowledgements
Thanks to
Lab Support Neeraj Gandhi Husam Katnani NIH Grant
EY015485 Gloria Foster Joe McFerron
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Thank you!
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-100 0 100 200 300 400 500 600 7000
100
200
300
400
Time from target onset (ms)
Activ
ity (
spik
es/s)
ControlFixation Blink -correctFixation Blink - earlyGapTask
-100 0 100 200 300 400 500 600 7000
100
200
300
400
500
600
700
Time from target onset (ms)
Activ
ity (
spik
es/s)
ControlFixation Blink - correctFixation Blink - earlyGapTask
Activity during “early” saccades
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0 100 200 7000
25
50
75
100
Time from target onset (ms)
Activ
ity (s
pike
s/s)
ControlFixation Blink
0
25
50
75
100
Activ
ity (s
pike
s/s)
0 100 200 700Time from target onset (ms)
ControlFixation Blink
Tar
Increased activity in SC location opposite to target