How do individuals with congenital - momilab › 2014 › 12 › lezione_sopramoda… · • How do...
Transcript of How do individuals with congenital - momilab › 2014 › 12 › lezione_sopramoda… · • How do...
•• How do individuals with congenital How do individuals with congenital
blindness form a conscious blindness form a conscious
representation of a world they have representation of a world they have
never seen?never seen?
•• WhatWhat happenshappens toto visualvisual--devoteddevoted brainbrain
structurestructure in in individualsindividuals whowho are are bornborn
depriveddeprived of of sightsight??
Match-to-SampleTask
(Haxby et al, J Neurosci, 1994)
Object and Spatial Visual Pathways in the Human Brain
Object Form Topography in Ventral Extrastriate Cortex Object Form Topography in Ventral Extrastriate Cortex
Are the topographically organized, Are the topographically organized,
categorycategory--related patterns of neural related patterns of neural
response in the ventral visual pathway a response in the ventral visual pathway a
representation of visual sensory images representation of visual sensory images
or a more abstract representation of or a more abstract representation of
object form that is not dependent on object form that is not dependent on
sensory modalitysensory modality??
fMRI: 3 Tesla GE scanner(GRE-EPI, TR= 2.5 sec, FOV= 24 cm, 3.5-mm sagittal slices, 8 runs of 174 volumes)
2 minutes 2 minutes 2 minutes
15 sec 15 sec
Simple exploration
One-back
Cortical regions activated during visual and/or Cortical regions activated during visual and/or tactile discrimination tasks in the sighted individualstactile discrimination tasks in the sighted individuals
Cortical areas activated during tactile Cortical areas activated during tactile discrimination in sighted and discrimination in sighted and congenitally blind individualscongenitally blind individuals
Sightedsubjects
Blindsubjects
Are patterns of neural activity elicited during tactile discrimination category-specific?
Is the category-specificity of patterns of neural response supramodal?
•• Ventral extrastriate cortex shows categoryVentral extrastriate cortex shows category--specific specific responses to the tactile exploration of objects responses to the tactile exploration of objects during a discrimination taskduring a discrimination task
•• Cortical areas involved in visual discrimination of Cortical areas involved in visual discrimination of objects are also involved in tactile discrimination of objects are also involved in tactile discrimination of the same objectsthe same objects
•• CategoryCategory--related patterns of response also in blind related patterns of response also in blind individuals who have had no visual experienceindividuals who have had no visual experience
÷÷ no merely due to visualno merely due to visual--based imagerybased imagery
÷÷ visual experience is not a previsual experience is not a pre--requisite for development requisite for development of categoryof category--related patterns of neural responserelated patterns of neural response
Object based representation in the ventral stream - Summary
Is this supramodal organization
restricted to ventral extrastriate cortex, or does it extend to
other “visual” areas?
ParietoParieto--occipitaloccipital cortexcortex
Block Design OneBlock Design One--back recognition taskback recognition taskRandomized stimuli presentation Randomized stimuli presentation
5 sec of visual exploration + 5 sec ISI5 sec of visual exploration + 5 sec ISI(24 matrices 2D or 3D)(24 matrices 2D or 3D)
VisualVisual
TaTacctiletile
10 sec of tactile exploration + 5sec ISI 10 sec of tactile exploration + 5sec ISI (16 matrices 2D or 3D)(16 matrices 2D or 3D)
SubjectsSubjects: 6 sighted and : 6 sighted and 44 congenitally blind rightcongenitally blind right--handed healthy volunteers handed healthy volunteers (mean (mean ageage±±sdsd= 28= 28±±1.3)1.3)
MRIMRI:: 1.5 Tesla GE scanner (GRE1.5 Tesla GE scanner (GRE--EPI; SPGR)EPI; SPGR)
Dorsal stream response to visualDorsal stream response to visualand tactile spatial location tasksand tactile spatial location tasks
Dorsal extrastriateDorsal extrastriate cortexcortex is activated bis activated bothothbyby optic and tactile spatial detection in optic and tactile spatial detection in
sighted and blind individualssighted and blind individuals
Ricciardi et al., Neuroscience, 2006
30 sec 20 sec
ST2sec
5secICI
1secISI
10 sec
Visual Task
30 sec 20 sec
ST4,5sec
5secICI
1secISI
15 sec
Tactile Task
Auditory Task
The The MentalMental Clock Task Clock Task forfor investigatinginvestigatingmultimodal multimodal spatial imageryspatial imagery in sighted anin sighted and d
congenitallycongenitally blindblind individualsindividuals
Bonino et al., in preparation
Similar Similar occipitooccipito--parietal parietal netwonetworksrks substainsubstainmultimodal multimodal spatial imageryspatial imagery in sighted anin sighted and d
congenitallycongenitally blindblind individualsindividuals
Visual
z= +41x=-49
PPC/IPS
Tactile
Auditory
PPC/IPS
z= +41x=-49
SightedSighted (n=1(n=10)0) Blind Blind (n=1(n=10)0)
These results demonstrate that dorsal extrastriate cortical areas are involved both in visual and tactile motion and spatial discrimination
Thus, similarly to ventro-temporal cortical regions, the dorsal pathway shows supramodal features, and therefore can process localization data independently from the sensory modality through which information is acquired
Spatial localization in the dorsal stream- Summary
Is this supramodal organization
restricted to ventral extrastriate cortex, or does it extend to
other “visual” areas?
hMT+hMT+
Coherent changes in visual images caused by object or viewer movement are called optic flow: it provides information about object form, position, orientation, and movement, as well as self-motion within the environment
Tactile exploration of the environment involves analogous changes in tactile images, or ‘tactile flow’:
÷ Object Form
÷ Position and movement
÷ Consistency
hMT+ responds to specific components of optic flow
We investigated whether the extrastriate visual cortical region, hMT+, plays a role in supramodal representation of sensory motion that is not mediated by visual mental imagery
We measured neural activity in sighted subjects during passive perception of optic and tactile motion in congenital and early blind subjects during perception of tactile motion
Subjects: 7 sighted and 4 congenitally blind healthy right-handed volunteers (26 ± 3 yr)
fMRI: 1.5 Tesla GE scanner GRE-EPITR= 3.0 sec, FOV= 24 cm 22-26 5-mm axial slices, 10-12 runs of 100 volumes
Rotational flow Translational flow
hMT+ is activated both by optic and tactile motion perception in sighted
Optic Flow
Tactile Flow
Tactile/OpticOverlap
Tactile motion activateTactile motion activates s hMT+hMT+ in in congenitallycongenitally blindblind subjectssubjects
Tactile Flow
Optic Flow
Tactile flow perception in sighted subjects activated the more anterior part of hMT+ but deactivated the more posterior part
By contrast, tactile flow perception in blind subjects activatedthe full extent of hMT+, including the more posterior part that is deactivated by tactile flow in sighted subjects
Tactile motion: summaryTactile motion: summary
Sighted Optic Flow Blind Optic FlowSightedTactileFlow
SSupramodalupramodal sensorysensory motionmotion
Poirier C et al., Neuroimage, 2006
Beuchamp MS et al., J Neurosci, 2007
Auditory Flow
Optic FlowTactile Flow
rTMSrTMS--mediated functional suppression of hMT+ mediated functional suppression of hMT+ impairs tactile flow discrimination in humansimpairs tactile flow discrimination in humans
0102030405060708090
100
1 2 3 4 mean
no-TMSControl-TMShMT-TMS
Accu
racy
of
resp
onse
GAP BETWEEN VELOCITIES
Gap: χ2(3)= 283.71, p.<0.01TMS: χ2(2)= 46.21, p.<0.01
TMS Experimental
condition (hMT+):
-49, -62, 5 mm
Control condition: 0, -76, 30
mm
Expe
rimen
t2
These results demonstrate that activation of hMT+ by tactile motion is not mediated by visual mental imagery and that the role of hMT+ in tactile motion perception can develop with no visual experience
Moreover, visual experience appears to lead to a segregation of hMT+ into an anterior subregion(MST?) that is involved in the representation of both optic and tactile motion and a posterior subregionthat is involved only in the representation of optic motion, possibly due to competitive interactions between visual and tactile inputs in normal development
Tactile motion: summaryTactile motion: summary
Conclusions -1
Overall, the results of these studies indicate that the cortex of the ventral and dorsal “visual” pathways are able to process information acquired through different sensory modalities, and is therefore organized in a more abstract supramodal fashion
This supramodal organization may also help to explain how individuals who have had no visual experience are able to acquire normal knowledge about objects and spatial representation, and interact effectively with the external world
Supramodal representation and plastic reorganization in the “visual” pathways in congenitally blind subjects
“what”ventral stream
Tactile Object Shape Recognition
“where”dorsal stream
Tactile/Auditory Spatial
Localization
Tactile/ Auditory Motion
Perception
Tactile recognition, linguistic, non-visual sensory and cognitive processes, such as for example Braille reading or verbal memory tasks
Action RecognitionImagery
Working Memory
If the extrastriate “visual” cortex is organized in a more abstract supramodal fashion, what
could we expect from higher-order cognitive functions that rely on the sensory processing
of these brain areas, such as working memory or mental imagery?
• Mirror neurons are a particular class of visuomotorneurons, originally discovered in area F5 of the monkeypremotor cortex, that discharge both when the monkeydoes a particular action and when it observes anotherindividual
Is visual experience necessary for the development of the mirror neuron system
in the human brain?
ExperimentalExperimental ParadigmParadigm
Stimuli•Action (sounds/movies)
•Environmental(sounds/movies)
•Motor Pantomime
• Upon completion of scanning, aurally presented actions were subdivided into motor familiar and motor unfamiliar, based on ratings provided by the two distinct groups
Task• Odd-ball motor execution and sound recognition (for sighted also visual)
Is MNS activated by sounds of familiar actions independently from visual experience?
p<0.05 corrected
FamiliarActionSounds
Is MNS response to aurally presented actions modulated by the degree of motor familiarity?
p<0.05 uncorrected
The effect of motor familiarity varies within the MNS regions
Sighted
Blind
Summary & ConclusionsSighted Blind
MNS response toaurally presentedactions does notdepend on visual
imagery or experience
Motor familiaritymodulates
magnitude of MNS response to
aurally presentedactions
Effect of familiarity varies
within the distinctregions of the MNS
ConclusionsConclusions --22
• Both congenitally blind and sighted individuals show overlapping networks subserving perceptual and higher-cognitive function
• Visual experience is not a necessary prerequisite for the development of the functional architecture of distinct cognitive abilities – supramodal organization
• These findings further expand previous data indicating that representation of the external world relies on supramodal cortical association areas and may contribute to explain why individuals who have had no visual experience interact effectively with the surrounding environment
ConclusionsConclusions --33
• The study of the blind brain has shed a bright light on many questions regarding not only plastic rearrangements but also functional organization of the sighted brain itself
• The blind brain should not be considered as a ‘disabled’ brain but rather as a truly ‘differentially able’ brain