•• 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