Talk outline Long-range horizontal network and the association field - - PowerPoint PPT Presentation

Talk outline

• Long-range horizontal network and the association field
• Electrophysiology, optical imaging : dynamics of

propagating waves

• A hypothesis
• Non invasive approach in human : Perception and MEG
• Functional role : reduced spike time variance
• Spike Time Aligment Model : STAM)

Psychophysics Anatomy

Mc Guire et al. 1991 Gilbert & Wiesel, 1989 Gilbert, 1992 Sincich & Blasdel, 2001 Schmidt & al, 1997

Physiology

Spikes/s

80 80

The -static- Association field : a multidiciplinary approach

Kapadia et al., 1995, 2000 Polat & al., 1998 Stemmler et al 1995, Somers et al. 1998, Dragoi et al 2000 Series et al., 2001

Modelling

Field et al 1993; Hess & Dakin 1997; Hess et al 1998; Kovacs & Julesz 1993,1994

Intracellular recordings in Cat area 17

Bringuier et al., Science, 1999

Iso-latency map

Optical recordings in Monkey V1 Grinvald & al., 1994; Glaser et al., 1999

Slow propagation wave of activity through intrinsic horizontal connections

Space-time map

0.1 to 0.5 m/s

The stimulus-evoked population response in visual cortex of awake monkey is a propagating wave

Lyle Muller, Alexandre Reynaud, Frédéric Chavane & Alain Destexhe (2014)

Voltage Sensitive Dye (VSD) imaging

Waves propagating through long range facilitation from “fast” neurons decreases the response latency of “slow” neurons

(Fast/slow : high/low contrast ; magno/parvo cells)

As a consequence the variance of the response latencies at the population level is reduced –and the overall population response latency is shortened. Decreased variance and overall shortened latencies increases the firing probability of neurons at later stages and provides the population with a phase advance, and a temporal mechanism for figure/ground segregation

A Hypothesis

Latency (ms)

200 100 0 50 100

Contrast Maunsell & al. (1999)

L1

Firing threshold Resting state

Cell 1

t1

Hypothesis

Propagating facilitation

Cell 2 L2

t2

Using apparent motion to decompose and measure spatial facilitation dynamics Fast/slow -> Early/late

Psychophysics: Perceptual correlates: apparent speed ? Magneto-encephalography: Correlates of propagating waves ?

Experiments

┴ // ┴ //

High contrast (50%) Low contrast (20%)

Using fast apparent motion to decompose and measure spatial facilitation dynamics Fast/slow -> Early/late

Perceptual correlate of propagating waves: apparent speed of fast apparent motion

0.6 0.8 1 1.2 1.4 50 100 50 100 0.6 0.8 1 1.2 1.4

% Test faster

Gabor patches ┴ path Gabor patches // path

High / High Low / Low Low / High High / Low

Contrasts

Test vs. Reference speed

Speed ratio

Psychophysics •8 participants •Reference speed: 60°/s •Test speeds: 36, 48, 60, 72 and 84°/s •2IFC Task: I1 or I2 faster ?

• Conditions: 4 Contrast pairs x 2 Orientations x 5 Speed ratios •20 trials per condition•2 Temporal Alternative Forced Choice

The speeding-up effect: interpretation

Result : Low contrast apparent motion sequences perceived faster than high contrast

sequences, BUT only for parallel sequences

Stimulus X1 T1 X2 T2 (T2=T1+dtphysical) V1 High contrast Lhigh1 short latency Lhigh2 =Lhigh1 +dt short latency Versus Low contrast Llow1 long latency Llow2 =Llow1+dt long latency BUT DECREASED by spatial facilitation => physiological T1-T2 delay, dtapparent, shorter than physical dt ! MT : Speed = dX/dtapparent Perceptual decision : low contrast sequences appear faster

L1

Cell 1

t1 Propagating facilitation

C ell 2 L2

t2

Latency (ms)

Contrast

Georges et al. 2001 Seriès et al 2001 Arnal & Lorenceau, unpublished data

High ┴ High // Low ┴ Low //

1300-1600 ms

ISI Fixation Fixation

533 ms 550-850 ms

High contrast (50%) Low contrast (20%)

C

Latency Amplitudes

Magneto-encephalography (MEG) : • 10 participants (2 excluded for bad signals) • Passive fixation

• Conditions: 2 Contrasts x 2 Gabor orientations x 2 hemifields • 112 trials per condition
• 151 axial magnetometers • Planar transformation • Individual sensor selection
• Non-parametric tests on amplitude, peak latency and half-height latency (p-values presented for Wilcoxon tests)

Magneto-encephalography: Correlates of propagating waves ?

S1 (140 ms) S3 (180 ms) S4 (180 ms) S5 (190 ms) S6 (170 ms) S7 (180 ms) S8 (160 ms) S9 (160 ms) S2 (140 ms) 200 fT S10 (160 ms) Stimulus: High ┴

Magneto-encephalography: Individual sensor selection

Magneto-encephalography: Results

17 ms Paradis et al. 2012

Magneto-encephalography: Source reconstruction Minimum Norm approach

Source localization compatible with a V1 origin

Interim conclusions

• Perceptual and MEG results point to a significant

influence of orientation and contrast on neural dynamics

• Phase advance for low contrast aligned Gabor

patches (~17 ms) similar to electrophysiological results

• Functional role, if any ?
• Motion processing ?
• Eye-movement planning ?
• Contour processing ?

Motion processing ?

• Speeding-up effect only seen for high speeds (~60°/s.), rarely

encountered in a natural environment

(except during retinal slip induced by saccadic eye-movement).

• Speeding-up effect only seen for low contrast apparent

motion and aligned elements, unlikely to contribute to motion interpretation

• Speeding-up effect: a side effect of neural dynamics

developing within intrinsic long-range connections?

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Collinear Orthogonal Target

Eye movements – speeding-up saccadic- planning ? A tentative experiment (Arnal & Lorenceau, unpublished data)

Latency

173 174 175 176 177 178 179

Mean Latencies ms.

Saccade duration

25 26 27

Duration ms.

Maximum Speed

278 279 280 281 282 283 284 285 Orthogonal Colinear

Gabor Orientation Max speed °/s

Saccade gain

104 105 106 107 108 Orthogonal Colinear

Gabor Orientation Saccade gain %

*

Eye movements – speeding-up saccadic- planning ? A tentative experiment (Arnal & Lorenceau, unpublished data)

• > No significant evidence of speeded saccadic eye-movements
• > Significant gain may reflect position uncertainty for aligned elements (inducing overshoot)

Saccadic generation mostly in Superior Colliculus, lacking orientation selectivity

Spatial facilitation and Spike-Time Alignment Model STAM

Fact: Contrast greatly varies along contours in natural images, implying an important latency variance at the population level, at odd with efficient integration of contours at later stages

(e.g. from V1 to V2)

Proposal: spatial facilitation between neurons responding to elongated contours with varying contrast favor (more) synchronized spiking

STAM:

Chain of integrate-and-fire neurons connected (or not) by long-range facilitatory connections

Testing STAM with the border of Lena’s hat

B A D C

Testing STAM with Lena’s hat

Contrast distribution along Lena’s hat

Paradis et al. 2012

Conclusions

STAM implements a biologically plausible spatial facilitation dynamics between neurons responding to contours of varying contrast, resulting in spike time alignment

(reduced latency variance at the population level).

Reduced latency variance, and the resulting overall phase advance,

• f the neuronal population processing elongated contours in V1

(relative to neurons responding to “noisy” background)

increases the probability, and reduces the latency, of firing at later processing stages, thus providing a temporal mechanism for figure/ground segregation. Earlier and more reliable responses of neurons at later stages (e.g. V2) that feedback onto V1 could in turn enhance the temporal contrast between contours and background