0

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Spike

den

sity (

sp/s

)

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Time from target onset (ms) Time from saccade onset (ms)

50 70 90 110 130 1500

100

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Time from target onset (ms) Time from saccade onset (ms)

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Neuron 1

Neu

ron

2

Neuron 3

Neuron 1

Neu

ron

2

Neuron 3

Neuron 1

Neu

ron

2

Neuron 3

Unstable population vector Stable population vector

0.4

1

Popu

latio

n st

abili

ty

SCFEF

0 100 200 300 400 −300 −200 −100 0 100

Time from target onset (ms) Time from saccade onset (ms)

0.4

1

caudal SC

rostral SC

+

Fixation Point

Stimulus

Eye

Express Regular

Gap

Time (ms)

0 100 200 300 400 −300 −200 −100 0 100

Time from target onset (ms) Time from saccade onset (ms)

0 100 200 300 400 −300 −200 −100 0 100

Time from target onset (ms) Time from saccade onset (ms)

Nor

mal

ized

spi

ke d

ensi

ty (s

p/s)

0

0.2

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0.6

0.8

1

0.4

1

Popu

latio

n st

abili

ty

0 100 200 300

Time from target onset (ms)

0 100 200 300

Time from target onset (ms)

0.4

1

Popu

latio

n st

abili

ty

0

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Spik

e de

nsity

(sp/

s)

rostral SC

caudal SC

0

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1

0.4

1

0

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1

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Time from target onset (ms) Time from saccade onset (ms)

Nor

mal

ized

spi

ke d

ensi

ty (s

p/s)

0

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1

SC

FEF

1

2

3

+

+

Fixation Point

Stimulus

Eye

. . .

Time (ms)

0 100 200 300 400 −300 −200 −100 0 100

Time from target onset (ms) Time from saccade onset (ms)

0

1

2

3

0

Fano

Fac

tor

Uday K. Jagadisan1,4 and Neeraj J. Gandhi1,2,3,4

Departments of Bioengineering1, Otolaryngology2, Neuroscience3, and the Center for Neural Basis of Cognition (CNBC)4, University of Pittsburgh, PA, 15213

Population temporal structure supplements the rate code during sensorimotor transformations

Funded by: NIH Grant EY022854

0 100 200 300 4000.1

0.2

0.3

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1

−300 −200 −100 0 100

0 100 200 300 400 −300 −200 −100 0 1000.1

0.2

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0.9

1

Time from target onset (ms) Time from saccade onset (ms)

Time from target onset (ms) Time from saccade onset (ms)

Popu

latio

n st

abili

tyPo

pula

tion

stab

ility

R1(t)R2(t)

.

.

.

Rn(t)

R1(t+τ)R2(t+τ)

.

.

.

Rn(t+τ)

. .

. .

R(t) R(t+τ)

. .

. .

R(t) R(t+τ).

R1(t)R2(t)

.

.

.

Rn(t)

R1(t+τ)R2(t+τ)

.

.

.

Rn(t+τ)

. .

. .

. .

. .

R1(t)R2(t)

.

.

.

Rn(t)

R1(t+τ)R2(t+τ)

.

.

.

Rn(t+τ)

. .

. .

. .

. .

- Neurons involved in sensorimotor processing produce bursts for both motor and non-motor events

- The mechanism by which downstream structures discriminate between sensory/cognitive and movement-related inputs in unknown

- We recorded from the frontal eye �elds (FEF) and superior colliculus (SC) in monkeys performing saccade tasks to probe this phenomenon

Delayed saccade task Mean population activity

Sensory burst

Motor burst

Why does the “sensory” burst not produce a movement?

The across trial reliability of spiking activity (measured by Fano Factor) does not explain the discrepancy.

Up close view of the population revealsa di�erence in the pattern of activity

The population code is temporally inconsistent during the visual burst and consistent during the motor burst

Instantaneous neuron shu�e

Temporal shu�e

Temporal stability in rostral SC shows the inverse pro�le

The visual burst is stable during “express”-like saccades

533.06 GG32

0.4

1

Popu

latio

n st

abili

ty

0 100 200 300 400 −300 −200 −100 0 100

Time from saccade onset (ms)Time from target onset (ms)

SC

FEF

SC+FEF

Caudal SC

plus rostral SCplus anti-RF

0 100 200 300 400 −300 −200 −100 0 100

Time from saccade onset (ms)Time from target onset (ms)

0.4

1

Popu

latio

n st

abili

ty

0

60

90

30

-90

-60

-30

5

20 40

2

10

0

60

90

30

-90

-60

-30

5

20 40

2

10

Introduction

n = 17, 1 monkey

n = 57, 2 monkeys

FEF

SC

Summary and Conclusions

Acknowledgements: Joe McFerron, Gloria Foster, Alexandra Maxim

Shu�e controls: the stabilty pro�le is speci�c to temporal structure in the real data

Combining all neurons from SC into one population - contralateral, ipsilateral, and rostral SC - preserves the stability pro�le

Temporal stability - dot product between time-separated population unit vectors

Red dots - point image of target location on SC mapBlue dots - location of neuron on SC based on stimulation-evoked vector

Combining neurons from SC and FEF preserves the pattern of temporal stability

Gap task

Temporal stability hypothesis: Stable population activity, coupled with an increase in �ring rate, is necessary for movement generation.The unstable visual burst could, in e�ect, increase the threshold for integration into a saccadic burst

- The sensory burst in visuomovement neurons in SC and FEF is unstable compared to the premotor burst. Thus, saccade generation requires stable population ac-tivity along with an increase in �ring rate.

- The reduction in population stability during the visual burst is attributable to the speci�c activity pattern in the recorded population.

- Neurons in rostral SC show the opposite pattern for large saccades - increased stability during the visual burst in caudal SC and decreased stability during the saccade.

- Population temporal structure is stable when a saccade is triggered o� the visual burst as in short latency sac-cades in the gap task.

- For more on how temporal structure could be decod-ed, go to poster 533.14 (HH4).

Rostral SC neurons are active during �xation and microsaccades and lower their activity for large saccades. They further reduce their drive during large movements by becoming unstable at the population level.