Spontaneous 2-dimensional carrier confinement at the n-type SrTiO3/LaAlO3 interface.

We describe the intrinsic mechanism of 2-dimensional electron confinement at the n-type SrTiO3/LaAlO3 interface as a function of the sheet carrier density n(s) via advanced first-principles calculations. Electrons localize spontaneously in Ti 3d(xy) levels within a thin (≲2 nm) interface-adjacent SrTiO3 region for n(s) lower than a threshold value n(c)∼10(14) cm(-2). For n(s)>n(c) a portion of charge flows into Ti 3d(xz)-d(yz) levels extending farther from the interface. This intrinsic confinement can be attributed to the interface-induced symmetry breaking and localized nature of Ti 3d t(2g) states. The sheet carrier density directly controls the binding energy and the spatial extension of the conductive region. A direct, quantitative relation of these quantities with n(s) is provided.

Chronic motor cortex stimulation in the treatment of central and neuropathic pain. Correlations between clinical, electrophysiological and anatomical data.

Thirty-two patients with refractory central and neuropathic pain of peripheral origin were treated by chronic stimulation of the motor cortex between May 1993 and January 1997. The mean follow-up was 27.3 months. The first 24 patients were operated according to the technique described by Tsubokawa. The last 13 cases (eight new patients and five reinterventions) were operated by a technique including localisation by superficial CT reconstruction of the central region and neuronavigator guidance. The position of the central sulcus was confirmed by the use of intraoperative somatosensory evoked potentials. The somatotopic organisation of the motor cortex was established peroperatively by studying the motor responses at stimulation of the motor cortex through the dura. Ten of the 13 patients with central pain (77%) and ten of the 12 patients with neuropathic facial pain had experienced substantial pain relief (75%). One of the three patients with post-paraplegia pain was clearly improved. A satisfactory result was obtained in one patient with pain related to plexus avulsion and in one patient with pain related to intercostal herpes zooster. None of the patients developed epileptic seizures. The position of the stimulating poles effective on pain corresponded to the somatotopic representation of the motor cortex. The neuronavigator localisation and guidance technique proved to be most useful identifying the appropriate portion of the motor gyrus. It also allowed the establishment of reliable correlations between electrophysiological-clinical and anatomical data which may be used to improve the clinical results and possibly to extend the indications of this technique.