Response of regional cerebral blood flow and oxygen metabolism to thalamic stimulation in humans as revealed by positron emission tomography

On the relation between sensory deafferentation, pain and thalamic activity in Wallenberg's syndrome: A PET-scan study before and after motor cortex stimulation

Decrease of thalamic blood flow contralateral to neuropathic pain has been described by several groups, but its relation with sensory deafferentation remains unclear. Here we report one instance where the thalamic effects of sensory deafferentation could be dissociated from those of neuropathic pain. A 50-year-old patient underwent a left medullary infarct leading to right-sided thermal and pain hypaesthesia up to the third right trigeminal division, as well as in the left face. During the following months the patient developed neuropathic pain limited to the left side of the face. Although the territory with sensory loss was much wider in the right (non painful) than in the left (painful) side of the body, PET-scan demonstrated significant reduction of blood flow in the right thalamus (contralateral to the small painful area) relative to its homologous region. After 3 months of right motor cortex stimulation the patient reported 60% relief of his left facial pain, and a new PET-scan showed correction of the thalamic asymmetry. We conclude that thalamic PET-scan hypoactivity contralateral to neuropathic pain does not merely reflect deafferentation, but appears related to the pain pathophysiology, and may be normalized in parallel with pain relief. The possible mechanisms linking thalamic hypoactivity and pain are discussed in relation with findings in epileptic patients, possible compensation phenomena and bursting thalamic discharges described in animals and humans. Restoration of thalamic activity in neuropathic pain might represent one important condition to obtain successful relief by analgesic procedures, including cortical neurostimulation.

Alterations of contralateral thalamic perfusion in neuropathic pain

Contralateral thalamus, the place of termination of spinothalamic tract, is affected in patients with pain. We employed single photon emission computed tomography (SPECT) to evaluate the thalamic perfusion in patients with spontaneous neuropathic pain. Ten patients with complex regional pain syndrome (CRPS) and eleven radiculopathiy patients were enrolled in this study. Regional cerebral blood flow of thalamus was assessed bilaterally by iodine-123-labelled iodoamphetamine SPECT. To standardize the inter-patient data, we set a contralateral thalamic uptake index (CTUI) for assessing thalamic asymmetry. In one study, we found elevation of CTUI in patients with symptoms of neuropathic pain for less than 12 month, whereas no change was observed in the case of a longer lasting disease. An another study demonstrated decrease of CTUI after pain treatment, even though it was unrelated to the pain intensity prior to treatment. Our SPECT study revealed that neuropathic pain altered thalamic neuronal activity. CTUIs were increased in early stage of the disease but decreased as the disease progressed to the chronic stage. These results suggest that CTUI can be used to improve management of neuropathic pain for proper evaluation of spontaneous pain.

Sustained neuronal activation raises oxidative metabolism to a new steady-state level: evidence from 1H NMR spectroscopy in the human visual cortex

To date, functional 1H NMR spectroscopy has been utilized to report the time courses of few metabolites, primarily lactate. Benefiting from the sensitivity offered by ultra-high magnetic field (7 T), the concentrations of 17 metabolites were measured in the human visual cortex during two paradigms of visual stimulation lasting 5.3 and 10.6 mins. Significant concentration changes of approximately 0.2 micromol/g were observed for several metabolites: lactate increased by 23%+/-5% (P<0.0005), glutamate increased by 3%+/-1% (P<0.01), whereas aspartate decreased by 15%+/-6% (P<0.05). Glucose concentration also manifested a tendency to decrease during activation periods. The lactate concentration reached the new steady-state level within the first minute of activation and came back to baseline only after the stimulus ended. The changes of the concentration of metabolites implied a rise in oxidative metabolism to a new steady-state level during activation and indicated that amino-acid homeostasis is affected by physiological stimulation, likely because of an increased flux through the malate-aspartate shuttle.

Temporal Analysis of Cortical Mechanisms for Pain Relief by Tactile Stimuli in Humans

The mechanisms by which vibrotactile stimuli relieve pain are not well understood, especially in humans. We recorded cortical magnetic responses to paired noxious (intra-epidermal electrical stimulation, IES) and innocuous (transcutaneous electrical stimulation, TS) stimuli applied to the back at a conditioning-test interval (CTI) of -500 to 500 ms. Results showed that IES-induced responses were remarkably attenuated when TS was applied 20-60 ms later and 0-500 ms earlier than IES (CTI = -60 to 500 ms). Since the signals evoked by IES reached the spinal cord (CTI = -60 to -20 ms conditions) and the cortex (-60 and -40 ms condition) earlier than those evoked by TS, the present results indicate that cortical responses to noxious stimuli can be inhibited by innocuous tactile stimuli at the cortical level, with minimal contribution at the spinal level.

Imaging oxygen consumption in forepaw somatosensory stimulation in rats under isoflurane anesthesia

The cerebral metabolic rate of oxygen (CMRO2) was dynamically evaluated on a pixel-by-pixel basis in isoflurane-anesthetized and spontaneously breathing rats following graded electrical somatosensory forepaw stimulations (4, 6, and 8 mA). In contrast to alpha-chloralose, which is the most widely used anesthetic in forepaw-stimulation fMRI studies of rats under mechanical ventilation, isoflurane (1.1-1.2%) provided a stable anesthesia level over a prolonged period, without the need to adjust the ventilation volume/rate or sample blood gases. Combined cerebral blood flow signals (CBF) and blood oxygenation level-dependent (BOLD) fMRI signals were simultaneously measured with the use of a multislice continuous arterial spin labeling (CASL) technique (two-coil setup). CMRO2 was calculated using the biophysical BOLD model of Ogawa et al. (Proc Natl Acad Sci USA 1992;89:5951-5955). The stimulus-evoked BOLD percent changes at 4, 6, and 8 A were, respectively, 0.5% +/- 0.2%, 1.4% +/- 0.3%, and 2.0% +/- 0.3% (mean +/- SD, N = 6). The CBF percent changes were 23% +/- 6%, 58% +/- 9%, and 87% +/- 14%. The CMRO2 percent changes were 14% +/- 4%, 24% +/- 6%, and 43% +/- 11%. BOLD, CBF, and CMRO2 activations were localized to the forepaw somatosensory cortices without evidence of plateau for oxygen consumption, indicative of partial coupling of CBF and CMRO2. This study describes a useful forepaw-stimulation model for fMRI, and demonstrate that CMRO2 changes can be dynamically imaged on a pixel-by-pixel basis in a single setting with high spatiotemporal resolution.

Neuroimaging With Calibrated fMRI

The conventional functional MRI (fMRI) map offers information indirectly about localized changes in neuronal activity because it reflects changes in blood oxygenation, not actual neuronal activity. To provide a neurophysiological basis of fMRI, researchers have used electrophysiology to show correlations of fMRI and electric signals. However, quantitative interpretation of the degree to which neuronal activity has changed still cannot be made from conventional fMRI data. The fMRI signal has 2 parts: one describes the correlation between oxidative metabolism (cerebral metabolic rate of oxygen [CMRO 2 ]) and cerebral blood flow (CBF), which supports the bioelectric work to sustain neuronal excitability; the other is the requisite dilation of blood vessels (cerebral blood volume [CBV]), which is the mechanical response involved in removal of waste while providing nutrients. Since changes in energy metabolism are related to bioelectric work, we tested whether spiking frequency of a neuronal ensemble (ν) is reflected by local energy metabolism (CMRO 2 ) in rat brain. We used extracellular recordings to measure Δν/ν and calibrated fMRI (ie, using fMRI signal, CBF, and CBV maps) to measure ΔCMRO 2 /CMRO 2 during sensory stimulation. We found that ΔCMRO 2 /CMRO 2 is ≈Δν/ν, which suggests efficient energy use during brain work. Thus, calibrated fMRI provides data on where and by how much the neuronal activity has changed. Possibilities of utilizing calibrated fMRI as a neuroimaging method are discussed.

Analgesia by electrostimulation of the trigeminal ganglion in patients with trigeminopathic pain: a PET activation study

Electrostimulation of the trigeminal ganglion (TGES) has shown good results in treatment of trigeminopathic pain in selected patients. To map the mechanisms of TGES analgesia, we determined changes in relative regional cerebral blood flow (rCBF) in ten patients with trigeminopathic pain using positron emission tomography. The patients were scanned before stimulation (habitual pain), after short-term stimulation (1 min, stTGES) and after long-term stimulation (ltTGES). Highly significant pain alleviation was reported after ltTGES. Relative rCBF changes after stTGES, which was without significant pain relief, were attributed mainly to intrinsic TGES effects. A statistical comparison of the subtraction images of ltTGES and stTGES disclosed significant rCBF increases after ltTGES in rostral parts of anterior cingulate cortex (ACC) and neighboring orbitofrontal and medial frontal cortices. Regression analysis of rCBF changes and subjective ratings of pain revealed an inverse relationship in the ipsilateral rostral ACC, and only rCBF changes in the caudal part of the contralateral ACC were consistent with the encoding of pain. The present study provides evidence for a pain modulating role of the rostral ACC, critically important in electrostimulation-induced analgesia, and identifies the caudal ACC as a region encoding pain sensation.

Differential modulation of subcortical target and cortex during deep brain stimulation

The combination of electrical deep brain stimulation (DBS) with functional imaging offers a unique model for tracing brain circuitry and for testing the modulatory potential of electrical stimulation on a neuronal network in vivo. We therefore applied parametric positron emission tomography (PET) analyses that allow characterization of rCBF responses as linear and nonlinear functions of the experimentally modulated stimulus (variable stimulator setting). In patients with electrodes in the thalamic ventrointermediate nucleus (VIM) for the treatment of essential tremor (ET) here we show that variations in voltage and frequency of thalamic stimulation have differential effects in a thalamo-cortical circuitry. Increasing stimulation amplitude was associated with a linear raise in rCBF at the thalamic stimulation site, but with a nonlinear rCBF response in the primary sensorimotor cortex (M1/S1). The reverse pattern in rCBF changes was observed with increasing stimulation frequency. These results indicate close connectivity between the stimulated nucleus (VIM) and primary sensorimotor cortex. Likewise, stimulation parameter-specific modulation occurs at this simple interface between an electrical and a cerebral system and suggests that the scope of DBS extends beyond an ablation-like on-off effect: DBS could rather allow a gradual tuning of activity within a neuronal circuit.

Oxidative and nonoxidative metabolism of excited neurons and astrocytes

There is evidence that the metabolic responses to afferent and efferent nervous activity are dissociated at sites of neuronal excitation in brain. Whether efferent activity follows afferent activity depends on the responsiveness of postsynaptic neurons, which in turn depends on the summation of excitatory and inhibitory postsynaptic potentials. The afferent activity excites the presynaptic terminals and astrocytes, whereas the efferent activity arises from excitation of the dendrites of projection neurons. Measurements in vivo indicate that primary stimulation, elicited by simple stimuli, gives rise to limited increases of energy metabolism associated with afferent activity. Reports show that a major consequence of afferent activity, in addition to the release of excitatory neurotransmitters from presynaptic terminals and the import of glutamate by astrocytes, is the establishment of rates of blood flow commensurate with increased rates of oxidative energy metabolism associated with efferent activity projecting from the site of activation. Increased flow rates overcome the inherent diffusion limitation of oxygen delivery, while increased rates of glycolysis elevate tissue pyruvate contents, to which oxygen consumption rates are matched. In vivo, neurons in the baseline condition sustain no net import of pyruvate or lactate, and the reported changes of metabolism subserving afferent and efferent activity are additive rather than linked by significant additional transfer of pyruvate or lactate from astrocytes. The dissociation of blood flow changes from efferent activity weakens the identification of functional states by changes of blood flow alone. It raises the possibility that uncoupling of flow from oxidative metabolism occurs at sites of low efferent activity, such that dissociations of flow and glycolysis from oxygen consumption signify imbalances of afferent and efferent activity.

Lactate efflux and the neuroenergetic basis of brain function

In the unstimulated brain energy is primarily supplied by the oxidation of glucose. However the oxygen-to-glucose index (OGI), which is the ratio of metabolic rates of oxygen to glucose, CMR(O2)/CMR(glc), diverges from the theoretical value of 6 as activity is increased. In vivo measurements of brain lactate show its concentration to increase with stimulation. The decreasing OGI with stimulation had led to the suggestion that activation, unlike resting activity, is supported by anaerobic glycolysis. To date a unifying concept that accommodates glucose oxidation at rest with lactate generation and OGI decrease during stimulation of brain is lacking. Furthermore, energetics that change with increasing activity are not consistent with a neuroenergetic model that has been proposed from 1-(13)C-glucose MRS experiments. That model, based upon in vivo MRS measurements and cellular studies by Pellerin and Magistretti, showed that glutamate neurotransmitter cycling was coupled to glucose oxidation over a wide range of brain activities from rest down to deep anesthesia. Here we reconcile these paradoxical observations by suggesting that anaerobic glucose consumption (which can provide energy rapidly) increases with activation to meet the power requirements of millisecond neuronal firing. It is proposed, in accord with our neuroenergetic model, that the extra glucose mobilized rapidly for glial clearance of glutamate, is not needed for the oxidative processes that are responsible for neuronal firing and glutamate release, and consequently it is effluxed as lactate. A stoichiometric relation between OGI and lactate concentration is derived from the neuroenergetic model, showing that the enhanced glucose uptake during activation is consistent with neuronal activity being energetically supported by glucose oxidation.

Functional imaging and neurophysiological assessment of spinal and brain therapeutic modulation in humans

We summarize here our experience in the neurophysiological and neuroimaging assessment of spinal and brain neuromodulation for pain relief. Techniques reviewed include somatosensory evoked potentials (SEPs), nociceptive spinal (RIII) reflexes, and positron emission tomography (PET), which have been applied both to investigate the mechanisms and to optimize the application of neurostimulation procedures. SEPs are especially useful in the preoperative assessment of patients with neuropathic pain, as they allow the establishment of the functional state of the dorsal column system. Patients with strongly abnormal SEPs due to ganglionic or preganglionic pathology are not likely to benefit from spinal (SCS) or peripheral (TENS) neurostimulation, because ascending fibers disconnected from their soma will undergo rapid degeneration and not be excitable. In the postoperative period, nociceptive spinal reflexes yield objective data concerning the effects of neurostimulation on spinal circuitry. In our experience, the best clinical results are achieved in patients with preserved preoperative SEPs, in whom neurostimulation entails profound attenuation of nociceptive reflexes.PET-scan imaging techniques have recently been used to demonstrate changes in cerebral blood flow during new neuromodulation schemes such as motor cortex stimulation for pain control (MCS). PET studies highlight the thalamus as the key structure mediating functional MCS effects. Thalamic activation would trigger a cascade of synaptic events influencing activity in other pain-related structures including the anterior cingulate gyrus, insula, and upper brainstem. The combination of clinical electrophysiology and functional neuroimaging provides insight into the mechanisms of action of neuromodulation procedures, guides clinical decision, and contributes to optimize patient selection.

Dependence of oxygen delivery on blood flow in rat brain: a 7 tesla nuclear magnetic resonance study

Magnetic resonance imaging (MRI) and spectroscopy (MRS) were used at a magnetic field strength of 7 T to measure CBF and CMRO2 in the sensorimotor cortex of mature rats at different levels of cortical activity. In rats maintained on morphine anesthesia, transitions to lower activity and higher activity states were produced by administration of pentobarbital and nicotine, respectively. Under basal conditions of morphine sulfate anesthesia, CBF was 0.75 +/- 0.09 mL x g(-1) x min(-1) and CMRO2 was 3.15 +/- 0.18 micromol x g(-1) x min(-1). Administration of sodium pentobarbital reduced CBF and CMRO2 by 66% +/- 16% and 61% +/- 6%, respectively (i.e., "deactivation"). In contrast, administration of nicotine hydrogen tartrate increased CBF and CMRO2 by 41% +/- 5% and 30% +/- 3%, respectively (i.e., "activation"). The resting values of CBF and CMRO2 for alpha-chloralose anesthetized rats were 0.40 +/- 0.09 mL x g(-1) x min(-1) and 1.51 +/- 0.06 micromol x g(-1) x min(-1), respectively. Upon forepaw stimulation, CBF and CMRO2 were focally increased by 34% +/- 10% and 26% +/- 12%, respectively, above the resting nonanesthetized values (i.e., "activation"). Incremental changes in CBF and CMRO2, when expressed as a percentage change for "deactivation" and "activation" from the respective control conditions, were linear (R2 = 0.997) over the entire range examined with the global and local perturbations. This tight correlation for cerebral oxygen delivery in vivo is supported by a recent model where the consequence of a changing effective diffusivity of the capillary bed for oxygen, D, has been hypothetically shown to be linked to alterations in CMRO2 and CBF. This assumed functional characteristic of the capillary bed can be theoretically assessed by the ratio of fractional changes in D with respect to changes in CBF, signified by omega. A value 0.81 +/- 0.23 was calculated for omega with the in vivo data presented here, which in turn corresponds to a supposition that the effective oxygen diffusivity of the capillary bed is not constant but presumably varies to meet local requirements in oxygen demand in a similar manner with both "deactivation" and "activation."

Activation of the anterior cingulate cortex by thalamic stimulation in patients with chronic pain: a positron emission tomography study

Object

Deep brain stimulation (DBS) of the sensory thalamus has been used to treat chronic, intractable pain. The goal of this study was to investigate the thalamocortical pathways activated during thalamic DBS.

Methods

The authors compared positron emission tomography (PET) images obtained before, during, and after DBS in five patients with chronic pain. Two of the five patients reported significant DBS-induced pain relief during PET scanning, and the remaining three patients did not report any analgesic effect of DBS during scanning. The most robust effect associated with DBS was activation of the anterior cingulate cortex (ACC). An anterior ACC activation was sustained throughout the 40 minutes of DBS, whereas a more posteriorly located ACC activation occurred at a delay after onset of DBS, although these activations were not dependent on the degree of pain relief reported during DBS. However, implications specific to the analgesic effect of DBS require further study of a larger, more homogeneous patient population. Additional effects of thalamic DBS were detected in motor-related regions (the globus pallidus, cortical area 4, and the cerebellum) and visual and association cortical areas.

Conclusions

The authors demonstrate that the ACC is activated during thalamic DBS in patients with chronic pain.

Activation of the anterior cingulate cortex by thalamic stimulation in patients with chronic pain: a positron emission tomography study

OBJECT

Deep brain stimulation (DBS) of the sensory thalamus has been used to treat chronic, intractable pain. The goal of this study was to investigate the thalamocortical pathways activated during thalamic DBS.

METHODS

The authors compared positron emission tomography (PET) images obtained before, during, and after DBS in five patients with chronic pain. Two of the five patients reported significant DBS-induced pain relief during PET scanning, and the remaining three patients did not report any analgesic effect of DBS during scanning. The most robust effect associated with DBS was activation of the anterior cingulate cortex (ACC). An anterior ACC activation was sustained throughout the 40 minutes of DBS, whereas a more posteriorly located ACC activation occurred at a delay after onset of DBS, although these activations were not dependent on the degree of pain relief reported during DBS. However, implications specific to the analgesic effect of DBS require further study of a larger, more homogeneous patient population. Additional effects of thalamic DBS were detected in motor-related regions (the globus pallidus, cortical area 4, and the cerebellum) and visual and association cortical areas.

CONCLUSIONS

The authors demonstrate that the ACC is activated during thalamic DBS in patients with chronic pain.

Stimulation of human thalamus for pain relief: possible modulatory circuits revealed by positron emission tomography

Stimulation of human thalamus for pain relief: possible modulatory circuits revealed by positron emission tomography. J. Neurophysiol. 80: 3326-3330, 1998. Stimulation of the somatosensory thalamus was used for more than 2 decades to treat chronic pain in the human. However, despite clinical reports of successful results, little is known about the actual mechanisms mediating this form of stimulation-produced analgesia. To reveal possible neuronal pathways evoked by thalamic stimulation, we measured regional changes in cerebral blood flow (rCBF) in five patients who received successful long-term relief of chronic pain with somatosensory thalamic stimulation. Positron emission tomography during thalamic stimulation revealed significant activation of the thalamus in the region of the stimulating electrodes as well as activation of the insular cortex ipsilateral to the thalamic electrodes (contralateral to the patients' clinical pain). For these patients, thalamic stimulation also evoked paresthesiae that included thermal sensations in addition to tingling sensations. Results of this study indicate that in some cases somatosensory thalamic stimulation may activate a thalamocortical pain modulation circuit that involves thermal pathways. These results are consistent with other recent reports suggesting that activation of thermal pathways may contribute to modulation of nociceptive information.

Calibrated functional MRI: mapping the dynamics of oxidative metabolism

MRI was extended to the measurement of changes in oxidative metabolism in the normal human during functionally induced changes in cellular activity. A noninvasive MRI method that is model-independent calibrates the blood oxygen level dependent (BOLD) signal of functional MRI (fMRI) against perfusion-sensitive MRI, using carbon dioxide breathing as a physiological reference standard. This calibration procedure provides a regional measurement of the expected sensitivity of the fMRI BOLD signal to changes in the cellular activity of the brain. Maps of the BOLD signal calibration factor showed regional heterogeneity, indicating that the magnitude of functionally induced changes in the BOLD signal will be dependent on both the local change in blood flow and the local baseline physiology of the cerebral cortex. BOLD signal magnitude is shown to be reduced by 32% from its expected level by the action of oxygen metabolism. The calibrated fMRI technique was applied to stimulation of the human visual cortex with an alternating radial checkerboard pattern. With this stimulus oxygen consumption increased 16% whereas blood flow increased 45%. Although this result is consistent with previous findings of a significant difference between the increase in blood flow and oxygen consumption, it does indicate clearly that oxidative metabolism is a significant component of the metabolic response of the brain to functionally induced changes in cellular activity.

Central representation of chronic ongoing neuropathic pain studied by positron emission tomography

This study was undertaken to explore whether the neural substrates demonstrated in brain imaging studies on experimentally induced pain are involved in the perception of chronic neuropathic pain. We investigated the cerebral representation of chronic lateralised ongoing pain in patients with painful mononeuropathy (PMN, i.e., pain in the distribution of a nerve, neuralgia) with positron emission tomography (PET), using regional cerebral blood flow (rCBF) as an index for neuronal activity. Eight patients (29-53 years) with PMN in the lower extremity (4 in the right, 4 in the left) were recruited. Paired comparisons of rCBF were made between the patient's habitual pain (HP) state and the pain alleviated (PA) state following a successful regional nerve block (RNB) with lidocaine. The ongoing neuropathic pain resulted in activation of bilateral anterior insula, posterior parietal, lateral inferior prefrontal, and posterior cingulate cortices as well as the posterior sector of the right anterior cingulate cortex (ACC), Brodmann area (BA) 24, regardless of the side of PMN. In addition, a reduction in rCBF was noted in the contralateral posterior thalamus. No significant change of rCBF was detected in the somatosensory areas, i.e., SI and SII. The cerebral activation pattern, while addressing the differences between the HP and PA states, emphasises the affective-motivational dimension in chronic ongoing neuropathic pain. The striking preferential activation of the right ACC (BA 24), regardless of the side of the PMN, not only confirms that the ACC participates in the sensorial/affectional aspect of the pain experience but also suggests a possible right hemispheric lateralisation of the ACC for affective processing in chronic ongoing neuropathic pain. Our data suggests that the brain employs different central mechanisms for chronic neuropathic pain and experimentally induced acute pain, respectively.

Cortical metabolism in posterolateral thalamic stroke: PET study

In 8 patients with small unilateral posterolateral thalamic (or, in one case, thalamocapsular) stroke (infarction or hemorrhage) selected on strict clinical (pure hemisomatosensory deficit without hemiparesis, visual field defect or neuropsychological impairment) and MRI criteria, we studied cortical energy metabolism using positron emission tomography with the 18F-fluorodeoxyglucose or the 15O-oxygen method. We found no significant ipsi- or contra-lateral metabolic depression either in the whole cortical mantle or in the sensorimotor cortex. These results support the hypothesis that location of thalamic stroke is a major determinant of the ipsilateral cortical hypometabolism characteristic of cognitively impaired patients with thalamic lesions and further emphasize the influence of the "non-specific" thalamocortical system on resting cortical metabolism. The lack of sensorimotor cortex hypometabolism in our patients suffering from hemidysesthesia and/or -hyperpathia also suggests that cortical metabolism is unaltered in thalamic pain.

Evidence for a common network of brain structures involved in parkinsonian tremor and voluntary repetitive movement

Repeated measurements of regional cerebral blood flow (rCBF) were obtained in 7 patients who underwent a stereotactic thalamic electrode implantation in the nucleus ventralis intermedius (nVIM) of the thalamus for severe hemi-parkinsonian tremor. Using positron emission tomography and oxygen-15 labelled water, rCBF was studied in each patient in two conditions: in absence of tremor, e.g. under nVIM electrical stimulation, and in presence of tremor. X-ray tomograms permitted individual definition of anatomical regions of interest. In presence of tremor, normalized rCBF increases were observed in the following regions: postcentral (13.6 +/- 8.4%, P = 0.0003), precentral (7.7 +/- 8.8%, P = 0.016), paracentral (7.7 +/- 8.4%), supplementary motor (8.2 +/- 10.4%, P = 0.025), caudate nucleus (5.7 +/- 7.6%, P = 0.03), vermis (9.7 +/- 7.3%, P = 0.007), cerebellar grey nuclei (9 +/- 6%, P = 0.016) on the electrode side and on the contralateral vermis (17.8 +/- 7.5%, P = 0.0003) and cerebellar grey nuclei (22 +/- 6.3%, P = 0.0004). These results clearly indicate an activation of the sensory-motor cortex, as well as an involvement of the supplementary motor area and the cortico-cerebellar pathways in Parkinsonian resting tremor (PRT). They demonstrate that PRT shares common network of brain structures with repetitive voluntary movement.

Chronic pain: a PET study of the central effects of percutaneous high cervical cordotomy

We have studied 5 patients with unilateral, severe chronic pain due to cancer before and after percutaneous, ventrolateral cervical cordotomy to investigate the central effects of the procedure. The aim was to identify the functional anatomical correlates of abolishing unilateral nociceptive input to the brain. Patients were investigated by positron emission tomography using C15O2 to evaluate cerebral blood flow. Comparisons were made between the patients with unilateral pain before cordotomy and normal volunteers. These demonstrated significantly less blood flow in 3 out of 4 of the individual quadrants of the hemithalamus contralateral to the side of pain (P less than 0.01-0.05). These differences were abolished by cordotomy. Comparison of the patients before and after cordotomy showed a significant decrease in blood flow in the dorsal anterior quadrant of the thalamus contralateral to the side of pain (P less than 0.05) which was normalised after cordotomy. There were no significant changes in the prefrontal or primary somatosensory cortex. We conclude that chronic pain results in a decrease of synaptic activity at thalamic level either from decreased activity in neurones projecting to that region and/or attenuated local neuronal firing. We have demonstrated no secondary remote effects in cortex, indicating the importance of subcortical mechanisms in central responses to chronic pain.

Brain single photon emission computed tomography: newer activation and intervention studies

Single-photon emission computed tomography (SPECT) regional cerebral blood flow (rCBF) findings using non-xenon 133 tracers in combination with activation and intervention techniques are reviewed. Examination of the currently available data indicates that it is possible to detect the effects of a variety of activations and interventional procedures using SPECT rCBF with non-xenon 133 tracers. There are still many issues to be resolved before SPECT can reach the level of sophistication attained by xenon 133 and positron emission tomography in studying rCBF during activation or intervention. However, research to date indicates that SPECT rCBF studied with tracers other than xenon 133 has an excellent potential for increasing the ability to differentiate normal and pathological states.