Diapositive 1

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Lattention
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SNS le paroxysme dun trouble attentionnel
Souvent associée à un problème au niveau du
cortex pariétal droit
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Lattention serait latéralisée
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1. Etude neuropsychologique de lattention
Lattention un gain de temps?
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2. Etudes neurobiologiques de lattention
- Spotlight - Object based
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2a.
Cortex pariétal, un siège de lattention?
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2b. Influence de lactivité cellulaire au niveau
du cortex visuel
Pourquoi V4?
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3. Effet de lattention au sein du cortex visuel
et études métaboliques
Protocoles
Résultats
Pas de variation de signal au niveau de V1, V2 ou
V3, et augmentation à partir de V4 (couleur,
forme..) ou MT (mouvement..)
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Eléments de discussion sur le phénomène
attentionnel
Modulation du gain (temps et intensité) Accentua
tion (sur stimulus efficace) Suppression
(efficace/inefficace) Descendant (cortex
pariétal)
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Résultats par électrophysiologie divergents

• Protocoles et questions posées
• Technologies limitées (au niveau spatial)
• Implication V4, TEO, (V5),
• très discuté V1, V2 ou V3 (Motter, 1993)
• (signal électrique produit par une image réduit
  lors de la présentation dune autre image)

Problème récurrent en IRMf
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Lattention et son exploration neurobiologique
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R. Desimone et J. Duncan modèle top-down bias
pour lattention
Intégration distribuée et compétitive à tous les
niveaux Compétition populations de neurones
codant pour les attributs dun même objet
pertinent sont facilitées, les autres
supprimées Contrôle descendant hormis le
contrôle ascendant (ex intensité du stimulus),
le contrôle descendant reposerait sur lamorçage
de populations neuronales représentant le
stimulus pertinent
Théorie prenant en compte les aspects
élémentaires des processi attentionnels
Descendant, modulation du gain, accentuation,
suppression
Où et doù
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Situation chez le singe Cortex V1, V2, V3, V4
Où ?
S2
S1
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Effet de lattention Situation chez le
singe Cortex V4, MT (et V1)
Où ?
S2
S1
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doù ?
Où ?
S1
TOP-DOWN Bias
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Où?
Mise en place de protocoles
Interactions suppressives
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V1 non affecté par le phénomène dattention?
a. Interaction suppressive et réciproque pour
représentation
- 2 stimulations vont sinhiber réciproquement
- stades de lintégration corticale extrastrié ?
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Protocole 1
2 X 2
Point de fixation tache
6 dexcentricité
Bobine 1.5 T
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Protocole 2
UT Uniform texture
ST Segregated texture
Line textures (8  8 deg in size, centered at
8 deg eccentricity)
The uniform texture contained line elements
(0.4  0.05 deg) at identical orientation
alternating at 1 Hz between 45 and 135 deg. The
boundaries of the checkerboard texture were
defined by the orientation difference between
line elements at 45 and 135 deg alternating at
1 Hz. In the actual experiment, bright lines were
presented on a dark background. Textures were
presented in blocks of 18 s interleaved with
blank periods.
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présentation de la texture et signal Bold
ST UT
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Problème de la taille du Champ Récepteur pour V2
et V1
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SSI with various display sizes. SSIs for display
sizes of 2  2, 4  4, 6  6, and 7  7,
presented to a quadrant, and of 6  6, presented
to a hemifield, for areas V1, V2, V4, TEO, and
V3A. With a display of 2  2, sensory
suppression was significant in all areas, but V1.
With a display size of 4  4, sensory
suppression was significant in V4, TEO, and V3A,
but not in V1 or V2. With display sizes of 6  6
and 7  7 within-a-quadrant, there were
significant suppressive interactions in TEO and
V3A, but not in the remaining areas. Finally, no
sensory suppression was seen with the 6  6
display presented to a hemifield in any of these
areas (6  6, HF).
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Champs supérieurs et inférieurs et interaction
suppressive
Effet de la présentation dun motif seul ou
associé dans le champ inférieur de trois images
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b. Attention dans un champ de lespace et signal
BOLD
Effet de lattention sur le signal BOLD au niveau
V1 et V4
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Moyenne des effets dans différentes structures du
cortex visuel
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Attention - réduit les interactions
suppressives - agit au niveau de V3, V4 et
TEO
Aucune modulation au niveau de V1 ?
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Et pourtant, V1 semble recruté (Watanabe et
coll., 1998)
Group of unidirectionally translating random dots
superimposed over another group of random dots
executing expansion motion. The white random dots
(48.0 cd/m2) moved against a black circular
background (0.5 cd/m2) whose diameter was 8.0 deg
in angular subtence. The speed of the dots
translating unidirectionally and those producing
expansion were both 15 deg/sec. The experiment
used 120 translating dots and 120 expanding dots.
Individual dots appeared for 150 msec and then
disappeared, to be replaced by others at random
locations. (Bobine 1.5 T)
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Effet de lattention sur Expansion vert ou sur la
translation (rouge) au niveau V1 et MT
Mouvement des yeux
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Activité de V1 modulable en accord avec Motter,
1993
Confirmation? Somers et coll., 1999
Protocole à base de disque avec lattention
portée sur représentation fovéale et extrafovéale
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1
3
a
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(a) Visual stimuli were composed of an annulus
and a central target. Radial wedge patterns were
rotated in the annulus. Single letters or a
fixation point appeared as the central target (b)
Scans consisted of nine 28-sec epochs. A fixation
target alone was passively viewed in the first
epoch. Attention was alternately directed to
foveal and extrafoveal regions of the stimulus
(a) in subsequent epochs. A fixation target alone
was passively viewed in the first epoch.
Attention was alternately directed to foveal and
extrafoveal regions of the stimulus (a) in
subsequent epochs. (c) Functional mapping of
visual eccentricity reveals a foveal
representation (shown in red see color key) in
the center of the patch, with more peripheral
eccentricities (up to 15o-20o) represented
inferiorly (upper visual field) and superiorly
(lower visual field). (d) Functional labeling of
retinotopic visual cortical areas identifies
areas V1 , V2 , V3 , and V3A, superior to the
calcarine sulcus, and areas V1, V2, VP, and
V4v, inferior to the calcarine. Upper and lower
visual field representations are indicated
by  and , respectively. (e and f) Patterns of
statistically significant increased activation
for attend extrafoveal motion vs. attend foveal
letters for both hemispheres of two example
subjects (color map shows P values).
Mid-eccentricity regions (green in c) of all four
visual field quadrants of V1 and higher visual
cortical areas exhibit highly significant
increases in activation. Dashed lines mark
iso-eccentricity contours. Solid lines mark
boundaries between neighboring cortical areas.
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Champ visuel supérieur
Champ visuel inférieur
Time course data by cortical area, averaged
across subjects (n  12 hemispheres) for attend
foveal letters vs. attend extrafoveal motion.
(a-h) Mid-eccentricity ROIs in V1 , V1, V2 ,
V2, V3 , VP, V3A, and V4v exhibited greater
activation during attend-extrafoveal-motion
epochs. (i) Confluent foveal representation
(e.g., red region of Fig. 2b) exhibited greater
activation during attend-foveal-letters epochs.
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Average attentional modulation amplitudes. Attend
extrafoveal motion -  passive viewing shown in
black. Passive viewing -  attend foveal letters
shown in white stacked on top of black bars.
Attend extrafoveal motion - attend foveal letters
shown in gray.
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Linfluence de lattention sur lactivité au
niveau de V1 a été confirmée récemment par
électrophysiologie. - protocoles ne
satisfont pas toujours la question
- implication relative et conditionnelle
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Attention au niveau de V1. Et avant ?
Kastner et coll., (2004) Functional imaging of
the human lateral geniculate nucleus and
pulvinar. J Neurophysiol. 91438-448.
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Mais alors,
Activité du LGN modulée par lattention?
?
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D. OConnor et coll., 2002 (Nature neurosciences)
Visual stimuli and experimental design.(a, b)
High- or low-contrast checkerboard stimuli were
presented to the left or right of a central
fixation point (). In experiments 1, 3 and 4,
subjects covertly directed attention to a
checkerboard arc (b, blue arrows) and detected
randomly occurring luminance changes along that
arc. The detection of luminance changes in low
contrast and high-contrast checkerboard stimuli
was not matched for task difficulty. (c) Axial
slice showing activations of the right
(green-blue) and left (yellow-orange) LGN and
visual cortex evoked by the checkerboard stimuli.
The coronal plane shows that activations in the
thalamus were restricted to the LGN no
activations within the pulvinar were obtained.
Scale indicates Z-score values of activations in
colored regions. R, right hemisphere.
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Time series of fMRI signals in the LGN (a-c) and
visual cortex (d-f). Group analysis (n 4). Data
from the LGN and visual cortex were combined
across left and right hemispheres. Activity in
visual cortex was pooled across areas V1, V2,
V3/VP, V4, TEO, V3A and MT/MST. (a, d)
Attentional enhancement. During directed
attention to the stimuli (red curves), responses
to both the high-contrast stimulus (100, solid
curves) and low-contrast stimulus (5, dashed
curves) were enhanced relative to an unattended
condition (black curves). (b, e) Attentional
suppression. During an attentionally demanding
fixation task (black curves), responses evoked by
both the high-contrast stimulus (100, solid
curves) and low-contrast stimulus (10, dashed
curves) were attenuated relative to an easier
attention task at fixation (green curves). (c, f)
Baseline increases. Baseline activity was
elevated during directed attention to the
periphery of the visual hemifield in expectation
of the stimulus onset (blue). Gray shades
indicate periods of checkerboard presentation.
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Attentional response modulation in the LGN and in
visual cortical areas V1, V2, V3/VP, V4, TEO, V3A
and MT/MST. Attentional effects were quantified
and normalized by defining several indices (a)
attentional enhancement index (AEI, experiment
1), (b) attentional suppression index (ASI,
experiment 2) and (c) baseline modulation index
(BMI, experiment 3). For all indices, larger
values indicate larger effects of attention.
Index values were computed for each subject based
on averaged signals obtained in the different
attention conditions and are presented as
averaged index values from four subjects (see
Methods). In visual cortex, attentional effects
increased from early to later processing stages.
Attentional effects in the LGN were larger than
in V1. Vertical bars indicate s.e.m. across
subjects. AEI (RATT - RUNATT)/(RATT RUNATT)
ASI (REASY - RHARD)/(REASY RHARD) BMI
REXP/RATT) R, response ATT, attended visual
presentations UNATT, unattended visual
presentations EASY, easy attention task HARD,
hard attention task EXP, expectation period.
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IIa. doù ?
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Type 2 ( endogène)
Type 1 ( exogène)
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