Artikel
Electrical excitability of the frontal cortex
Elektrische Erregbarkeit des frontalen Kortex
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Autoren
Veröffentlicht: | 4. Mai 2005 |
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Gliederung
Text
Objective
Contrary to the general clinical view, there is considerable overlapping of primary motor units over a cortical area much broader than the “classical” narrow motor strip along the central sulcus. In the present study, direct cortical stimulation was applied to determine the electrical excitability of the frontal cortex.
Methods
Electrical stimulation of the frontal cortex was performed in 35 patients during surgery in the central region. The central sulcus (CS) was identified by somatosensory evoked potential (SEP) phase reversal. Cortical motor mapping was first performed by monopolar anodal stimulation with a train of 500 Hz (7 - 10 pulses) followed by bipolar stimulation (pulses at 60 Hz with max. 4 sec train duration). Surgery was performed under general anesthesia without muscle relaxants. Action potentials were recorded from the forearm flexor, thenar and quadriceps muscles contra- and ipsilateral to the side of stimulation. The motor areas identified were divided into three categories: (1st): areas located in the primary motor cortex (PMC), which defined as Brodmann areas 4 and 6aα; (2nd): areas located in the secondary motor cortex (SMC), defined as Brodmann areas 6aβ and 8 and (3rd): areas located in the supplementary motor cortex (SuMC), defined as Brodmann areas 9, 45, 44.
Results
Of 315 motor responses elicited by electrical cortical stimulation, 51.5% (162) were located in the PMC, 44.4% (140) outside the motor strip in the SMC, and 4.1% (13) in the SuMC. In all the motor responses from the PMC (162/162) action potentials were recorded only from the contralateral muscles, whereas in 35/140 of the responses from the SMC action potentials were recorded from the ipsilateral muscles.
Conclusions
There is a high concentration of pyramidal cells in the precentral gyrus but also a significant number distributed throughout the frontal and parietal lobe. Contrary to the general clinical view, there is considerable overlapping of motor units over a cortical area much broader than the “classical” narrow motor strip along the central sulcus. Thus anatomic orientation must, whenever possible, be complemented by intraoperative mapping of all these areas in order to prevent postoperative motor deficits.