Frontal Fibers Connecting the Superior Frontal Gyrus to Broca Area: A Corticocortical Evoked Potential Study.
BACKGROUND
The frontal aslant tract is a deep frontal pathway connecting the superior frontal gyrus (SFG) to Broca area. This fiber is assumed to be associated with language functions, especially speech initiation and spontaneity. The aim of this study was to electrophysiologically investigate this network using corticocortical evoked potentials (CCEPs).


METHODS
This study enrolled 8 patients with brain tumors or medically intractable focal epilepsies who underwent frontal craniotomy over the language-dominant side. All patients underwent CCEP recordings during tumor resection or during invasive evaluation for epilepsy surgery. Alternating 1-Hz electrical stimuli were delivered to pars opercularis (pO) and pars triangularis (pT), corresponding to Broca area, and SFG via the subdural grid electrodes with intensity of 10 mA. Electrocorticograms from SFG and pO/pT time-locked to 50 stimuli were averaged in each trial to obtain CCEP responses.


RESULTS
In all patients, stimulation of pO/pT induced CCEP responses in SFG. CCEP responses were recorded in lateral SFG in 5 patients and in supplementary motor areas in 4 patients. Reciprocality was observed in 7 patients in the stimulation of SFG. CCEP responses were significantly faster at SFG from pO/pT than at pO/pT from SFG (Wilcoxon signed rank test, P = 0.028).


CONCLUSIONS
The present study demonstrated a corticocortical network connecting Broca areas and SFG in a reciprocal manner. Our findings might provide new insight into language and motor integration.
['Ookawa|Satoshi|S|', 'Enatsu|Rei|R|', 'Kanno|Aya|A|', 'Ochi|Satoko|S|', 'Akiyama|Yukinori|Y|', 'Kobayashi|Tamaki|T|', 'Yamao|Yukihiro|Y|', 'Kikuchi|Takayuki|T|', 'Matsumoto|Riki|R|', 'Kunieda|Takeharu|T|', 'Mikuni|Nobuhiro|N|']
D000328:Adult D000368:Aged D000369:Aged, 80 and over D001932:Brain Neoplasms D065711:Broca Area D056324:Diffusion Tensor Imaging D004828:Epilepsies, Partial D005071:Evoked Potentials D005260:Female D006801:Humans D007806:Language Disorders D008279:Magnetic Resonance Imaging D008297:Male D008875:Middle Aged D011183:Postoperative Complications D017397:Prefrontal Cortex D011930:Reaction Time D055815:Young Adult
Superior frontal gyrus Broca area Frontal aslant tract Supplementary motor area Electric cortical stimulation