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Clin Neurophysiol. 2005 Nov;116(11):2664-74. Epub 2005 Oct 10.

Short and middle-latency Median Nerve (MN) SEPs recorded by depth electrodes in human pre-SMA and SMA-proper.

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  • 1Fondazione Santa Lucia, IRCCS, Rome, Italy.



To analyse waveforms, latencies and amplitudes of Median Nerve (MN) SEPs recorded by stereotactically electrodes implanted in the SMA of 14 epileptic patients (9 in pre-SMA,3 in SMA-proper, 2 in both) in order to evaluate which short and middle-latency SEPs are generated in this area and which could be the physiological relevance of these responses.


Short and middle-latency MN SEPs were recorded by chronically implanted electrodes in the fronto-temporal cortex and in particular in the mesial frontal region of 14 drug-resistant epileptic patients. MN stimulations of 100 micros were delivered by skin electrodes at the wrist; stimulus intensity was adjusted slightly above the motor threshold.


The main result of this study is that middle-latency SEPs were originated in pre-SMA but not in SMA-proper as demonstrated by both referential and bipolar recordings. In particular off-line computed bipolar traces between neighbouring contacts implanted in the pre-SMA and in the frontal external regions showed a phase reversal at the deepest contacts located in pre-SMA. Conversely, bipolar recordings between neighbouring contacts implanted in the SMA-proper and in the frontal external regions showed inversion recovery at more superficial contacts, implanted in area 6. Finally, we confirmed that no short-latency MN SEP (and in particular the N30) is originated in the whole SMA.


Among premotor areas, somatosensory inputs seem to reach pre-SMA and area 6 but not SMA-proper.


This study assessed that no scalp SEP in the first 100 ms after MN stimulus could be generated in SMA-proper.

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