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1 2,3 3 1 3 1 Anne-Dominique , Charles , Juliane , Florian , Denis Brunet , Christoph M. and Eric M. 3 Gindrat Quairiaux Britz Lanz Michel Rouiller 1 Unit of Physiology, Department of Medicine, University of Fribourg, Fribourg, Switzerland 2 Faculty of Medicine, Department of Fundamental Neurosciences, University of Geneva, Geneva, Switzerland 3 Functional Brain Mapping Laboratory, Departments of Clinical and Fundamental Neuroscience, Geneva University Hospital, Geneva, Switzerland Recordings of scalp somatosensory evoked potentials in macaque monkeys with a high-density electrode array Supported by Swiss National Science Foundation grant 310000-110005 (EMR) and NCCR Neuro Conclusion These data show that SSEPs can be successfully and reproducibly recorded from a high-density EEG cap in macaque monkeys. Moreover, the inverse solution algorithm allowing source localisation seems to be a very promising tool to better understand the different mechanisms involved in cortical reorganisation. The experiment will continue with the permanent cortical lesion performed in the near future in a first monkey, followed by regular post-lesional SSEP recordings in parallel with motor performance assessment in the acute phase and in the recovery phase until the animal reaches a post-lesional behavioural plateau. [email protected] Introduction Somatosensory evoked potential (SSEP) recordings from the scalp are commonly used in human for clinical applications. They are among others good predictor of outcome after a brain injury such as stroke. Recordings from the scalp with a high-density electrode array are also relevant for research purposes to reveal the time course of evoked topographies. In this pilot study, we made a transposition of this simple and minimally invasive tool to macaque monkeys, allowing repeated monitoring of the brain activity from the whole scalp surface using a multichannel electrode array. The goal of the present study was to allow repeated assessment of the cortical activity in the context of a central nervous system lesion. It is expected that SSEPs will allow to assess the post-lesional cortical reorganisation of neuronal networks and relate it to functional recovery, following a motor cortex lesion. ? As expected, voltage topographies obtained after sti- mulation on one side are essentially mirror images of those of the other side in relation to the antero- posterior axis. ? The voltage topography of the responses obtained after either median or tibial nerve stimulations is in line with the somatotopical organisation of the senso- rimotor cortex. ? Similar pre-lesional data were obtained in two other animals. ? Post-craniotomy voltage topographies do not show any artefact and are similar to pre-lesional maps, indi- cating that the craniotomy itself does not have any strong adverse effect on the recorded SSEPs. ? The first version of the inverse solution model shows an appropriate localisation of the main cortical activity after tibial nerve stimulation, that is to say in the leg representation of the sensorimotor cortex. First data of inverse solution Grand average of pre-lesional right tibial nerve SSEPs in a single monkey I. SSEP recordings ? ? Recordings with a customised EEG cap containing 33 electrodes regu- larly distributed over the scalp ? 2.5% sevoflurane anaesthesia ? Electrical stimulations to the median nerve at the wrist or to the tibial nerve at the ankle, successively on each side (0.5 Hz repetition rate, intensity slightly above the visible motor threshold, total of 75 sweeps) Three adult macaque monkeys (Macaca fascicularis) Results Post-craniotomy SSEPs Left tibial nerve stimulation (Grand average of 8 recordings) Left median nerve stimulation (Grand average of 8 recordings) Right median nerve stimulation (Grand average of 8 recordings) Left median nerve stimulation (Grand average of 29 recordings) (4.0 msec 9.0 msec 26.4 msec) (5.6 msec) (10.4 msec) (12.8 msec) (14.4 msec) (16.2 msec) A - 10m V + 12 345 - 1 m V + B C Mean voltage maps obtained by cluster analysis, with onset time 1 - + 1 4 3 2 5 6 Time post-stimulus (msec) 5 10 20 30 40 50 60 4 6 Overlapped waveforms of all 33 channels 1 Global Field Power (4.0 msec 9.0 msec 24.8 msec) (5.6 msec) (9.8 msec) (11.8 msec) (13.6 msec) (15.8 msec) A - 10m V + 12 345 - 1 m V + B C Mean voltage maps obtained by cluster analysis, with onset time 1 - + 1 4 3 2 5 6 Time post-stimulus (msec) 5 10 20 30 40 50 60 4 Overlapped waveforms of all 33 channels 1 6 6 Global Field Power Right median nerve stimulation (Grand average of 30 recordings) Right tibial nerve stimulation (Grand average of 8 recordings) Right tibial nerve stimulation (Grand average of 29 recordings) Left tibial nerve stimulation (Grand average of 31 recordings) Pre-lesional SSEPs Overlapped waveforms and the voltage topography at 21.8 msec (maximum of the GFP peak) are represented on the left part. The right windows show different views of the source estimation on MRI at this same time point. All the present data were acquired in a single monkey. Materials and methods III. SSEP data analysis and source estimation ? (http://sites.google.com/site/fbmlab/cartool) and com- puted against the average reference. ? k-means cluster analysis of the SSEP voltage maps (data-driven approach revealing a series of scalp topo- graphies reflecting the steps in information proces- sing) ? LAURA (local autoregressive average) inverse solu- tion algorithm with LSMAC (Locally Spherical Model with Anatomical Constraints) head model SSEPs data were analysed with the Cartool software posterior anterior left right Map orientation II. Lesion ? Future permanent unilateral lesion performed in the hand representation of M1, requiring a craniotomy ? “Sham lesion” consisting in the craniotomy alone, with bone flap resuture and fixation with bone substitute HydroSet (Stryker®) A R L P (4.0 msec 24.8 msec) (5.4 msec) (8.6 msec) (10.0 msec) (12.6 msec) (15.0 msec) A - 10m V + 12 45 - 1m V + B C Mean voltage maps obtained by cluster analysis, with onset time 1 1 4 3 2 5 6 Time post-stimulus (msec) 5 10 20 30 40 50 60 4 Overlapped waveforms of all 33 channels 6 3 Global Field Power - + - 1 m V + B C A Mean voltage maps obtained by cluster analysis, with onset time Overlapped waveforms of all 33 channels - 10m V + 1 4 Time post-stimulus (msec) 2 3 5 3 1 10 20 30 40 50 60 6 1 4 5 2 Global Field Power (6.0 msec 40.6 msec) (26.6 msec) (29.4 msec) (16.6 msec) (11.4 msec) - + 2 3 - 1 m V + B C A Mean voltage maps obtained by cluster analysis, with onset time Overlapped waveforms of all 33 channels - 10m V + 1 + Time post-stimulus (msec) 10 20 30 40 50 60 6 1 4 5 Global Field Power (6.0 msec 41.4 msec) (28.0 msec) (30.0 msec) (16.2 msec) (11.2 msec) 1 4 2 3 5 - 2 3 - 1 m V + B C A Mean voltage maps obtained by cluster analysis, with onset time Overlapped waveforms of all 33 channels - 10m V + 1 4 Time post-stimulus (msec) 10 20 30 40 50 60 6 2 3 5 1 4 1 5 Global Field Power (27.2 msec) (28.4 msec) (15.4 msec) (10.8 msec) (6.0 msec 31.8 msec) + - 2 3 - 1 m V + B C A Mean voltage maps obtained by cluster analysis, with onset time Overlapped waveforms of all 33 channels - 10m V + 1 + 1 4 Time post-stimulus (msec) 10 20 30 40 50 60 6 2 3 5 1 45 Global Field Power (6.0 msec 32.2 msec) (27.6 msec) (29.4 msec) (15.8 msec) (11.0 msec) - (4 msec 28.2 msec) (5.6 msec) (10.8 msec) (13.8 msec) (16.0 msec) (17.8 msec) A - 10m V + 12 3 45 - 1m V + B C 1 - + Time post-stimulus (msec) 5 10 20 30 40 50 60 4 6 Overlapped waveforms of all 33 channels Global Field Power 7 1 4 3 2 5 6 7 (24.8 msec) Mean voltage maps obtained by cluster analysis, with onset time
