SEEG electrode shaft affects amplitude and latency of potentials evoked with single pulse electrical stimulation.

BACKGROUND: Long and thin shaft electrodes are implanted intracerebrally for stereoelectroencephalography (SEEG) in patients with pharmacoresistant focal epilepsies. Two adjacent contacts of one of such electrodes can deliver a train of single pulse electrical stimulations (SPES), and evoked potentials (EPs) are recorded on other contacts. In this study we assess if stimulating and recording on the same shaft, as opposed to different shafts, has an impact on common EP features. NEW METHOD: We leverage the large volume of SEEG data gathered in the F-TRACT database and analyze data from nearly one thousand SEEG implantations in order to verify whether stimulation and recording from the same shaft influence the EP pattern. RESULTS: We found that when the stimulated and the recording contacts were located on the same shaft, the mean and median amplitudes of an EP are greater, and its mean and median latencies are smaller than when the contacts were located on different shafts. This effect is small (Cohen's d ∼ 0.1), but robust (p-value < 10-3) across the SEEG database. COMPARISON WITH EXISTING METHOD(S): Our study is the first one to address this question. Due to the choice of commonly used EP features, our method is congruent with other studies. CONCLUSIONS: The magnitude of the reported effect does not obligate all standard analyses to correct for it, unless they aim at high precision. The source of the effect is not clear. Manufacturers of SEEG electrodes could examine it and potentially minimize the effect in their future products.

Cholinergic and Nadph-δ neurons in the pedunculopontine and laterodorsal tegmental nuclei of human and nonhuman primates.

The brainstem pedunculopontine (PPN) and laterodorsal tegmental (LDTg) nuclei are involved in multifarious activities, including motor control. Yet, their exact cytoarchitectural boundaries are still uncertain. We therefore initiated a comparative study of the topographical and neurochemical organization of the PPN and LDTg in cynomolgus monkeys (Macaca fascicularis) and humans. The distribution and morphological characteristics of neurons expressing choline acetyltransferase (ChAT) and/or nicotinamide adenine dinucleotide phosphate diaphorase (Nadph-δ) were documented. The number and density of the labeled neurons were obtained by stringent stereological methods, whereas their topographical distribution was reported upon corresponding magnetic resonance imaging (MRI) planes. In both human and nonhuman primates, the PPN and LDTg are populated by three neurochemically distinct types of neurons (ChAT-/Nadph-δ+, ChAT+/Nadph-δ-, and ChAT+/Nadph-δ+), which are distributed according to a complex spatial interplay. Three-dimensional reconstructions reveal that ChAT+ neurons in the PPN and LDTg form a continuum with some overlaps with pigmented neurons of the locus coeruleus, dorsally, and of the substantia nigra (SN) complex, ventrally. The ChAT+ neurons in the PPN and LDTg are -two to three times more numerous in humans than in monkeys but their density is -three to five times higher in monkeys than in humans. Neurons expressing both ChAT and Nadph-δ have a larger cell body and a longer primary dendritic arbor than singly labeled neurons. Stereological quantification reveals that 25.6% of ChAT+ neurons in the monkey PPN are devoid of Nadph-δ staining, a finding that questions the reliability of Nadph-δ as a marker for cholinergic neurons in primate brainstem.