Jiří Vrána

Functional magnetic resonance imaging of cerebral activation during spinal cord stimulation in failed back surgery syndrome patients

Spinal cord stimulation (SCS) consisting of electrical stimulation of the dorsal spinal cord using epidural electrodes has been shown to relieve chronic neuropathic pain. To analyze the cerebral activation patterns related to SCS, and to evaluate the effects of SCS on the processing of acute experimental pain, we performed functional magnetic resonance imaging (fMRI) on eight patients suffering from failed back surgery syndrome who were also being treated with SCS for severe pain in their legs and lower back. Three types of stimulation were used, each lasting 36s: (i) SCS, (ii) heat pain (HP) applied to the leg affected by neuropathic pain, and (iii) simultaneous HP and SCS.

EEG source analysis and fMRI reveal two electrical sources in the fronto-parietal operculum during subepidermal finger stimulation

Using functional magnetic resonance imaging (fMRI) and electroencephalographic (EEG) source dipole analysis in 10 normal subjects, two electrical source dipoles in the contralateral fronto-parietal operculum were identified during repetitive painful subepidermal stimulation of the right index finger. The anterior source dipole peaking at 79 +/- 8 ms (mean +/- SD) was located in the frontal operculum, and oriented tangentially toward the cortical surface. The posterior source dipole peaking at 118 +/- 12 ms was located in the upper bank of the Sylvian fissure corresponding to the second somatosensory cortex (S2). The orientations of the posterior source dipoles displayed large variability, but differed significantly (P < 0.05) from the orientations of the anterior source dipoles. Electrical sources and fMRI clusters were also observed in ipsilateral fronto-parietal operculum. However, due to low signal-to-noise ratio of ipsilateral EEG sources in individual recordings, separation of sources into anterior and posterior clusters was not performed. Combined fMRI and source dipole EEG analysis of individual data suggests the presence of two distinct electrical sources in the fronto-parietal operculum participating in processing of somatosensory stimuli. The anterior region of the fronto-parietal operculum shows earlier peak activation than the posterior region.

Effects of spinal cord stimulation on the cortical somatosensory evoked potentials in failed back surgery syndrome patients

OBJECTIVE To evaluate the functional activation of the somatosensory cortical regions in neuropathic pain patients during therapeutic spinal cord stimulation (SCS). METHODS In nine failed back surgery syndrome patients, the left tibial and the left sural nerves were stimulated in two sessions with intensities at motor and pain thresholds, respectively. The cortical somatosensory evoked potentials were analyzed using source dipole analysis based on 111 EEG signals. RESULTS The short-latency components of the source located in the right primary somatosensory cortex (SI: 43, 54 and 65ms) after tibial nerve stimulation, the mid-latency SI component (87ms) after sural nerve stimulation, and the mid-latency components in the right (approximately 161ms) and left (approximately 168ms) secondary somatosensory cortices (SII) were smaller in the presence of SCS than in absence of SCS. The long-latency source component arising from the mid-cingulate cortex (approximately 313ms) was smaller for tibial and larger for sural nerve stimuli during SCS periods compared to periods without SCS. CONCLUSIONS SCS attenuates the somatosensory processing in the SI and SII. In the mid-cingulate cortex, the effect of SCS depends on the type of stimulation and nerve fibers involved. SIGNIFICANCE Results suggest that the effects of SCS on cortical somatosensory processing may contribute to a reduction of allodynia during SCS.

Source imaging of the cortical 10 Hz oscillations during cooling and warming in humans.

Primary cold and warm afferent fibers show a robust overshoot in their firing during periods of temperature change, which subsides during tonic thermal stimulation. Our objective was to analyze cortical activation, on a scale of hundreds of milliseconds, occurring during the process of dynamic cooling and warming, based on an evaluation of the amplitude changes seen in 10 Hz electroencephalographic oscillations. Eleven right-handed subjects were exposed to innocuous cold ramp stimuli (from 32 degrees C to 22 degrees C, 10 degrees C/s) and warm ramp stimuli (32 degrees C to 42 degrees C, 10 degrees C/s) on the thenar region of their right palm, using a contact thermode. EEG was recorded from 111 scalp sites, and the 10 Hz current source densities were modeled using low-resolution electromagnetic tomography. During cooling, the earliest amplitude decreases of 10 Hz oscillations were seen in the contralateral posterior insula and secondary somatosensory cortex (SII), and the premotor cortex (PMC). During warming, the earliest events were only observed in the PMC and occurred approximately 0.7 s later than during cooling. Linear regression analysis between 10 Hz current source densities and temperature variations revealed cooling-sensitive activation in the bilateral posterior insula, PMC and the anterior cingulate cortex. During warming, the amplitude of 10 Hz oscillations in the PMC and posterior insula correlated with stimulus temperature. Dynamic thermal stimulation activates, in addition to the posterior insula and parietal operculum, the lateral PMC. The activation of the anterior cingulate cortex during cooling may aid in the anticipation of the cold temperature end-point and provide continuous evaluation of the thermal stimulus.

Cortical oscillatory changes during warming and heating in humans.

Warmth and heat are registered by different types of cutaneous receptors. To disentangle the cortical activation patterns of warming and heating, we analyzed the temporal evolution of the electroencephalographic 10 and 20 Hz oscillations with the time resolution of hundreds of milliseconds. Sixty heat (from 32 to 50.5 degrees C, rate of change 6 degrees C/s) and warm (from 32 to 42 degrees C, 6 degrees C/s) stimuli were applied on the right thenar using contact thermode. EEG was recorded from 111 scalp electrodes in 12 healthy subjects, and analyzed using event-related desynchronization and low-resolution electromagnetic tomography methods. During warming, the amplitudes of 10 and 20 Hz oscillations over the contralateral primary sensorimotor (SI/MI) and premotor cortices decreased, and the amplitude of 20 Hz oscillations in the anterior cingulate and ipsilateral premotor cortex increased. Heating was associated with additional profound amplitude decreases of 10 and 20 Hz oscillations over SI/MI and premotor cortex, and by amplitude increase of 20 Hz oscillations originating in the posterior cingulate cortex. Results suggest biphasic amplitude changes of the cortical oscillations during ramp increase of temperature attributable to the periods of warming and heating. The amplitude decreases of 10 and 20 Hz oscillations in SI/MI and premotor cortex possibly aid in preparation of motor withdrawal reaction in an event that temperature should reach intolerable pain. Synchronization of the 20 Hz oscillations in the anterior and especially in the posterior cingulate cortex may aid suppression of unwanted movements.

Somatosensory-evoked potentials are influenced differently by isometric muscle contraction of stimulated and non-stimulated hand in humans

Chronic pain is associated with motor dysfunctions, and stimulation of the motor cortex has been shown to alleviate chronic pain. Recently Nakata et al. [Pain 107 (2004) 91-98] showed differentiated patterns of neuromagnetic evoked fields following painful laser stimulation during phasic movements of stimulated and non-stimulated hand. Phasic movements and static contractions differ in their functional activation of the motor cortices. Therefore, we decided to analyze the effects of isometric contractions of intrinsic right and left hand muscles on cortical sources of somatic-evoked potentials related to a painful galvanic stimulation of the right middle finger. Using spatio-temporal source dipole analysis of 111 electroencephalographic signals in 10 right-handed men, source activities were evaluated in the left primary somatosensory cortex (S1), left (S2(L)) and right (S2(R)) secondary somatosensory cortex, anterior cingulate cortex (ACC) and posterior cingulate cortex (PCC). Ipsilateral hand muscle contraction was associated with a decrease of source activity in S1 and with subsequent increases in S2(L) and the PCC. Contralateral hand muscle contraction was accompanied by a decrease of source activity in bilateral S2 cortices followed by decreases in the S1 and anterior cingulate cortex. Results suggest early suppression of source activity in S1 during ipsilateral hand muscle contractions and in bilateral S2 during contralateral hand muscle contractions.

An interaction of nucleons at an energy between 1014 and 1015 eV/nucleon

A jet (0+14)α with primary energy {3.3− 2.2+ 5.3}. 1014eV/nucl. was observed in the “I”-stack. An interaction with very small multiplicity (ns=3or 4)found in the axis of the jet is probably caused by another nucleon from the α-primary. 10 particles of the narrow cone have opening angles of some 10−4radians, 4 particles in the diffuse cone are emitted at angles of a few 10−2radians. A pronounced anisotropy exists in the C. M. system. The coefficient of inelasticity ≈ 0.1was calculated directly extrapolating the measured energies of secondaries. The interpretation of the whole event is in good agreement with Heisenbergs theory of multiple production of particles.

267 MODIFICATION OF CORTICAL EVOKED POTENTIALS DURING SURAL NERVE STIMULATION IN FAILED BACK SURGERY SYNDROME PATIENTS TREATED WITH SPINAL CORD STIMULATION

We analyzed whether cortical processing of cutaneous sural nerve stimuli would be altered by spinal cord stimulation (SCS) in patients with failed back surgery syndrome. In nine patients (4 women, 5 men, age 39–56 years) suffering from intractable pain in their left leg and back, the left sural nerve was stimulated with 0.2 ms square pulses (13–34mA) and 5–8 s inter-stimulus intervals. The evoked potentials (111 EEG electrodes), that were recorded during ongoing SCS or in absence of SCS, were modeled using BESATM (MEGIS, Germany). The source model encompassed four source dipoles located in the following regions: the right primary somatosensory cortex (S1, 87ms), the left and right secondary somatosensory cortex (S2, 161 and 167ms, respectively), and the mid-cingulate cortex (314ms). The source amplitudes of the S1 and of both S2 source dipoles were reduced during periods of SCS compared to periods without SCS (P< 0.05). In contrast to the S1 and S2 sources, the amplitude of the mid-cingulate source was increased during SCS (P< 0.05). Subjective intensity of sural nerve stimuli, evaluated using visual analogue scale, was not affected by SCS (P> 0.05). While reduced amplitudes of S1 and S2 sources during SCS suggest inhibition of afferent input possibly occurring at segmental level, the increased source activity in the cingulate cortex points to a positive interaction between SCS and the sural nerve stimulation. These cortical activation changes are not associated with subjective intensity measures of the sural nerve stimuli. Supported by GAUK 66/2005, IGA 8232, RG 0021620816, LC 550 and CNS 1M0517.

250 CEREBRAL ACTIVATION DURING SPINAL CORD STIMULATION AND HEAT PAIN IN FAILED BACK SURGERY SYNDROME PATIENTS

Spinal cord stimulation (SCS) is an established treatment for chronic neuropathic pain. However, in recent studies conflicting results regarding the effect of SCS were noted in a selected group of patients suffering from Complex Regional Pain Syndrome and mechanical allodynia. In the present study we investigated the pain relieving effect of SCS in a rat experimental model of neuropathic pain as related to the severity of mechanical allodynia. Adult male rats (n = 45) were submitted to a unilateral sciatic nerve ligation. The level of allodynia was tested using the withdrawal response to tactile stimuli with the von Frey test. A portion of these rats developed marked tactile hypersensitivity in the nerve-lesioned paw (von Frey test), similar to “tactile allodynia” observed after nerve injury in humans. Then prior to SCS treatment the rats were subdivided into three groups based on the level of allodynia: mild, moderate and severe. All allodynic rats (n = 27) were treated with SCS for 30min (f = 50Hz; pulse with 0.2ms and stimulation at 2/3 of motor threshold) at 16 days post-injury. Our data demonstrate a differential effect of SCS related to the severity of the mechanical allodynia. SCS leads to a faster and better pain relief in mildly allodynic rats as compared to the more severely allodynic rats. Thus, we suggest that the selection and subdivision of patient groups similar to those defined in our experimental setting (mild, moderate and severe allodynic) may provide better pre-treatment prediction of possible therapeutic benefits of SCS.

Energy spectrum of electron pairs in a high energy photon-electron cascade

The energy spectrum of electron pairs generated in a high energy photon-electron cascade up to a depth of 1·5 c. u. was measured and the possible influence of the medium on the shape of the spectrum according to Landau-Pomerančuk-Ter Mikaelyan and Migdal was investigated. Two procedures were used for the analysis; no significant deviation from the Bethe-Heitler spectrum could be observed. Different ways of estimating the primary energy were applied; the resulting value, 2×1012eV, was accepted as the primary energy.AbstractИзмерялся энергетич еский спектр электро нных пар, возникающих в высокоэнергетичес ком электронно-φотонном ливне вплоть до глуби ны 1,5 ливневых единиц о т вершины ливня и исследовалос ь возможное влияние с реды на φорму спектра по ЛандауПомеранчук у, Тер-Микаеляну и Мигда лу. Анализ осуществля лся двумя методами; никакого существенн ого отклонения от спе ктра Бэте-Гейтлера на блюдать не удалось. Для определе ния первичной энерги и были использованы р азличные методы; в качестве первичной энергии было принято значение 2⋅1012 eV.