The graphemic/motor frontal area Exner's area revisited.
OBJECTIVE
In 1881, Exner first described a "graphic motor image center" in the middle frontal gyrus. Current psycholinguistic models of handwriting involve the conversion of abstract, orthographic representations into motor representations before a sequence of appropriate hand movements is produced. Direct cortical stimulation and functional magnetic resonance imaging (fMRI) were used to study the human frontal areas involved in writing.


METHODS
Cortical electrical stimulation mapping was used intraoperatively in 12 patients during the removal of brain tumors to identify the areas involved in oral language (sentence reading and naming) and writing, and to spare them during surgery. The fMRI activation experiment involved 12 right-handed and 12 left-handed healthy volunteers using word dictation (without visual control) and 2 control tasks.


RESULTS
Direct cortical electrical stimulation of restricted areas rostral to the primary motor hand area (Brodmann area [BA] 6) impaired handwriting in 6 patients, without disturbing hand movements or oral language tasks. In 6 other patients, stimulation of lower frontal regions showed deficits combining handwriting with other language tasks. fMRI also revealed selective activation during word handwriting in left versus right BA6 depending on handedness. This area was anatomically matched to those areas that affected handwriting on electrical stimulation.


CONCLUSIONS
An area in middle frontal gyrus (BA6) that we have termed the graphemic/motor frontal area supports bridging between orthography and motor programs specific to handwriting.
Roux
Franck-Emmanuel
FE
INSERM, University of Toulouse, France. franck_emmanuel.roux@yahoo.fr
Dufor
Olivier
O
Giussani
Carlo
C
Wamain
Yannick
Y
Draper
Louisa
L
Longcamp
Marieke
M
Démonet
Jean-François
JF
D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D005625:Frontal Lobe / Q000502:physiology; D006236:Handwriting; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D055815:Young Adult