Transcranial magnetic stimulation of the occipital pole interferes with ver

bal processing in blind subjects

Amir Amedi, Agnes Floel, Stefan Knecht, Ehud Zohary & Leonardo G Cohen

협동과정 뇌과학 곽영빈

Background information

• Visual cortex has a more prominent role in processing nonvisual tasks in blind than in sighted

• fMRI studies show occipital cortex activation during verbal generation, memory, and language-related tasks in blind

• Strong correlation between V1 activity and verbal tas

ks in blinds suggest the contribution of V1 in supramodal cognitive operations

Purpose of study

• To identify the causal link between early visual cortex activity and successful performance on verbal tasks

– Compared the effect of virtual legion (rTMS) of specific cortical sites on the performance of a verb-generation task in early blind and sighted control

– rTMS of the occipital pole increased the error rate in verb-generation task in blind subjects, but not in sighted controls

Barker, 1984Barker, 1984

Transcranial Magnetic Stimulation allows the Safe, Non-invasive and Transcranial Magnetic Stimulation allows the Safe, Non-invasive and Painless Stimulation of the Human Brain Cortex.Painless Stimulation of the Human Brain Cortex.Electromagnetic induction generates disorder into a normally ordered system

Repetitive Transcranial Magnetic Stimulation

Experimental design

• rTMS application– Lt posterior calcarine (V1)– Lt lateral occipital (LO)– Lt inferior prefrontal (PF)– Rt primary somatosensory

(S1, cortical control site)– Midfrontal region (sham)

• Outcome measures– Error rate – Accuracy score ((sham

-condition)/sham)– Reaction time

Methods

• 9 early-blind (lost sight before 4 yrs old or congenitally) subjects and 9 sighted subjects matched for age, sex, handedness and education

• TMS coil positioning determined by use of a MRI-guided, stereotactic device with subthreshold intensity

• Verb-generation task – 200 nouns per subject, 40 nouns per rTMS site (respon

d with appropriate verb within 5s)

– The order of rTMS sites counterbalanced between subjects, stimuli sets rotated across conditions and subjects and matched between blind and sighted

Data analysis

• ANOVARM of STIMULATION SITE(sham/S1/V1/LO/PF) and between-subject factor GROUP(blind/sighted)

– Error rate

– Normalized accuracy rate

– Reaction time from noun onset

– Reaction time from rTMS onset

– Motor output distortions

• Post hoc analysis with correction for multiple comparisons

Effects of rTMS on verbal processing

rTMS of V1 compared to sham and S1 stimulation resulted in larger error rates in the blind subjects. rTMS of PF resulted inlarger error rates in the sighted control subjects

Subanalysis of error types

Semantic and morphosyntactic errors occurred in approximately the same proportion in sham and S1 sites in both groups. In the blind group, rTMS of V1 resulted in significantly more semantic errors. In the sighted group, rTMS of PF resulted in significantly more semantic errors.

Discussion

• rTMS of the occipital pole reduced accuracy in a verb-generation task with semantic processing affected the most in blind subjects.

• Connections between extrastriate visual areas and prefrontal cortex exist. Connectivity between the two areas is enhanced in blind.

• Reduced performance during rTMS of V1 would be due to disruption of the network.

• Early retinotopic areas are recruited in the processing of higher-level cognitive functions in early blind individuals.