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


METHODS
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.


RESULTS
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.


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


CONCLUSIONS
This study assessed that no scalp SEP in the first 100 ms after MN stimulus could be generated in SMA-proper.
Barba
C
C
Fondazione Santa Lucia, IRCCS, Rome, Italy. carmen.barba@tiscali.it
Valeriani
M
M
Colicchio
G
G
Mauguière
F
F
D000328:Adult; D001931:Brain Mapping; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004827:Epilepsy / Q000503:physiopathology*; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008475:Median Nerve / Q000503:physiopathology*; D009044:Motor Cortex / Q000503:physiopathology*; D011930:Reaction Time