Feeling by sight or seeing by touch?
We have addressed the role of occipital and somatosensory cortex in a tactile discrimination task. Sight-ed and congenitally blind subjects rated the roughness and distance spacing for a series of raised dot patterns. When judging roughness, intermediate dot spacings were perceived as being the most rough, while distance judgments generated a linear relation. Low-frequency rTMS applied to somatosensory cortex disrupted roughness without affecting distance judgments, while rTMS to occipital cortex disrupted distance but not roughness judgments. We also tested an early blind patient with bilateral occipital cortex damage. Her performance on the roughness determination task was normal; however, she was greatly impaired with distance judgments. The findings suggest a double-dissociation effect in which roughness and distance are primarily processed in somatosensory and occipital cortex, respectively. The differential effect of rTMS on task performance and corroborative clinical evidence suggest that occipital cortex is engaged in tactile tasks requiring fine spatial discrimination.
Merabet
Lotfi
L
Laboratory for Magnetic Brain Stimulation, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA.
Thut
Gregor
G
Murray
Brian
B
Andrews
Jessica
J
Hsiao
Steven
S
Pascual-Leone
Alvaro
A
D000328:Adult; D000704:Analysis of Variance; D001766:Blindness / Q000503:physiopathology; D001931:Brain Mapping; D004192:Discrimination, Psychological / Q000502:physiology; D004215:Distance Perception / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D006801:Humans; D008280:Magnetics; D008297:Male; D009778:Occipital Lobe / Q000502:physiology; D010812:Physical Stimulation / Q000379:methods; D011597:Psychomotor Performance / Q000502:physiology / Q000528:radiation effects; D012677:Sensation / Q000502:physiology*; D013003:Somatosensory Cortex / Q000502:physiology* / Q000528:radiation effects; D014110:Touch / Q000502:physiology*; D014785:Vision, Ocular / Q000502:physiology*