Hubert Preißl

Neuroimaging of chronic pain: phantom limb and musculoskeletal pain

New developments in brain imaging lead to a better understanding of cortical and subcortical processes involved in pain perception and the establishment of chronic pain. For different forms of chronic pain long-term changes in cortical structures have been described. In patients with phantom limb pain and back pain alterations in the somatotopic organization of the primary somatosensory (SI) could be observed. The amount of this reorganization is correlated with the subjective pain rating. These changes, which are based on processes of neuronal plasticity, can partially be reversed by analgesic interventions. For the investigation of cortical processes concerning reorganization, EEG and MEG methods are most suitable because of their high temporal and spatial resolution. In conclusion, these findings open a new way for therapeutic interventions to prevent the development of chronic pain.New developments in brain imaging lead to a better understanding of cortical and subcortical processes involved in pain perception and the establishment of chronic pain. For different forms of chronic pain long-term changes in cortical structures have been described. In patients with phantom limb pain and back pain alterations in the somatotopic organization of the primary somatosensory (SI) could be observed. The amount of this reorganization is correlated with the subjective pain rating. These changes, which are based on processes of neuronal plasticity, can partially be reversed by analgesic interventions. For the investigation of cortical processes concerning reorganization, EEG and MEG methods are most suitable because of their high temporal and spatial resolution. In conclusion, these findings open a new way for therapeutic interventions to prevent the development of chronic pain.

Explaining aphasias in neuronal terms

Abstract Neuronal derangement causing aphasia is simulated by means of lesions in artificial networks patterned according to the neuroanatomy of the language cortex. Linguistic elements are assumed to have their neuronal counterparts in Hebbian cell assemblies comprising neurons of disparate cortical regions. The simulations correctly predict that aphasic symptoms (like non-fluent speech production, speech perception deficit, agrammatism, anornia) vary as a function of the cortical lesion site. Implications for brain theory are discussed.

Understanding the reward system functioning in anorexia nervosa: crucial role of physical activity.

Hyperactivity is a potential neurobiological marker and a core psychopathological trait in anorexia nervosa (AN). We investigated the processing of hyperactivity-related information in fifteen AN patients, 15 athletes and 15 non-athletes to examine if they represent disorder-related reward information using eye tracking. We assessed the extent of individually performed physical activity, mood, trait reward sensitivity and serum leptin levels. Results revealed a pronounced bias in overall attentional engagement toward stimuli associated with physical activity in patients and athletes as compared to non-athletes. In patients, relevant correlations were found: trait reward sensitivity and attentional orienting were strongly correlated and amount of physical activity correlated with attentional orienting and engagement. Compared to non-athletes, patients and athletes rated exercise stimuli as more pleasant. Findings suggest that exercise-related stimuli are perceived as rewarding by AN patients. Positive motivational valence of physical activity might contribute to disorder development and maintenance.

Early activation of the primary somatosensory cortex without conscious awareness of somatosensory stimuli in tumor patients.

The primary sensory cortex has usually been regarded as a necessary step in the information processing stream leading to conscious awareness. Recently, it has been proposed that that higher order associative areas rather than the primary sensory areas are the neural basis of conscious perception. In two patients with tumors near the central region we recorded magnetic somatosensory evoked fields. Magnetic source imaging revealed early (40 ms) neural activation in primary somatosensory cortex and absence of later (>60 ms) neural activation in the primary and associative areas in these patients. None of the patients showed conscious awareness of somatosensory stimuli applied to the corresponding body site although the first component of the evoked field was within normal limits. The time course of the magnetic responses and additional evidence on intensity ratings of somatosensory stimuli suggest that early activity in the primary somatosensory cortex is not sufficient for conscious experience to emerge.

Effects of water on cortical excitability in humans

The effects of water on cortical excitability, measured using magnetoencephalographic recordings, were investigated in a sample of 19 healthy volunteers in a double‐blind, placebo experiment comparing water with saline solution. Spontaneous magnetoencephalogram as well as auditory‐evoked magnetic fields were recorded before and after the drinking of 750 mL water (9 subjects) or saline solution (10 subjects) and during and after hyperventilation following the drinking conditions. Hyperventilation was used to enhance the hypothesized synchronizing effect of water on spontaneous magnetoencephalographic activity. In addition, the magnetic fields were measured during a dichotic listening task under attended and unattended conditions. The prediction, that intake of water, because of induced cell swelling, will increase neuronal excitability and lead to an increased synchronization of the spontaneous magnetoencephalogram during hyperventilation was confirmed. Hyperventilation induced an increase of spectral power in all frequency bands particularly theta and delta power after water drinking. Furthermore, there was an increase of magnetic mismatch negativity (MMNm) amplitude in attended conditions and a simultaneous decrease in unattended conditions after water drinking. N1m (magnetic N1 wave) revealed significant changes during experimental conditions: increase after drinking and decrease after hyperventilation in both groups. MMNm for attended conditions showed a high positive correlation with osmolality changes (difference in the mol solute per kg water before and after drinking); N1m and PNm (magnetic processing negativity) as well as MMNm for unattended conditions showed significant correlations with subjective ratings of thirst and mood state.

Gamma-Band Responses Reflect Word/Pseudoword Processing

According to one brain-theoretical view, higher brain functions are based on processing units called cell assemblies. Cell assemblies are large groups of cortical pyramidal neurons with strong and reciprocal internal connections. Cell assemblies develop in a randomly connected neuronal network when sets of neurons are frequently active simultaneously so that their connections strengthen (Hebb’s law, Hebb, 1949, Gustafsson et al., 1987, Bonhoffer et al., 1989, Ahissar et al., 1992). Neurons making up one assembly do not need to be located in a small cortical area. They may be distributed widely over various cortical regions. Such transcortical assemblies are likely to be held together through long axons of pyramidal cells which are well-known to connect distant cortical areas (Pandya and Yeterian, 1985, Braitenberg and Schuz, 1991, Deacon, 1992a, Deacon, 1992b). Due to strong intra-assembly connections, excitation of some neurons of an assembly leads to spreading activation in the network and, finally, to an “ignition” of the whole assembly. Overshooting activity will occur in the cortex when too many assemblies ignite at the same time. Therefore, a regulation mechanism is required which keeps the level of cortical excitation close to a target value (Braitenberg, 1978). This regulation mechanism guarantees that only one or a limited number of assemblies will ignite at a time.

Magnetenzephalographie in der NeurochirurgieEin Routineprotokoll zur präoperativen Planung und intraoperativen Navigation

Zusammenfassung: Die Magnetenzephalographie (MEG) ermöglicht in Kombination mit der Magnetresonanztomographie (MRT) die Lokalisation und funktionelle Charakterisierung der Zentralregion. Aufgrund des großen apparativen und zeitlichen Aufwandes konnte sich dieses Verfahren bisher in der neurochirurgischen Routine nicht durchsetzen. Ziel der hier vorgestellten Arbeit war daher die Entwicklung eines Protokolls, welches die Integration funktioneller MEG-Daten in die Planung und Durchführung von neurochirurgischen Operationen als Routinemethode ermöglicht.Es wurden 45 Patienten mit Raumforderungen im Bereich der Zentralregion im MEG untersucht. Die somatosensorische Lokalisation erfolgte über die elektrische Stimulation des Nervus tibialis und des Nervus medianus. Für die motorische Lokalisation wurden von den Patienten Bewegungen des Zeigefingers durchgeführt. Die Ortskoordinaten wurden auf einen 3D-MRT-Datensatz übertragen und markiert. Abschließend erfolgte die Übertragung dieses markierten MRT-Datensatzes auf den Rechner des neurochirurgischen Navigationssystems. Unter Anwendung des hier vorgestellten Protokolls standen dem Neurochirurgen nach durchschnittlich drei Stunden alle relevanten Daten sowohl zur präoperativen Planung als auch zur intraoperativen Navigation zur Verfügung.Die Ergebnisse zeigen, dass die auf MEG und MRT basierende funktionelle Neuronavigation in der täglichen neurochirurgischen Routine eingesetzt werden kann.Abstract: The combination of magnetoencephalography (MEG) and magnetic resonance imaging (MRI) allows the localization and functional characterization of the somatosensory and motor cortex. However, this method is technically pretentious and time consuming. Therefore, functional imaging is still not established as routine procedure in neurosurgery. The aim of the presented study was the development of a protocol, which allows the integration of functional MEG data into presurgical planning and intraoperative navigation, as a routine method.Forty-five patients with intracranial mass lesions within the central region were examined by MEG. For the somatosensory localization, the median and tibial nerves were electrically stimulated. The motor cortex was localized by tapping of the index finger. The coordinates of the functional dipole source were projected onto a 3D MRI data-set. Finally, the marked MR images were transferred to the neurosurgical navigation system. Following this strategy, after an average time of 3 hours, all data for presurgical planning and intraoperative navigation were available for the neurosurgeon.Our results show that MEG/MRI based functional neuronavigation can be used as a routine tool during daily neurosurgical practice.The combination of magnetoencephalography (MEG) and magnetic resonance imaging (MRI) allows the localization and functional characterization of the somatosensory and motor cortex. However, this method is technically pretentious and time consuming. Therefore, functional imaging is still not established as routine procedure in neurosurgery. The aim of the presented study was the development of a protocol, which allows the integration of functional MEG data into presurgical planning and intraoperative navigation, as a routine method.Forty-five patients with intracranial mass lesions within the central region were examined by MEG. For the somatosensory localization, the median and tibial nerves were electrically stimulated. The motor cortex was localized by tapping of the index finger. The coordinates of the functional dipole source were projected onto a 3D MRI data-set. Finally, the marked MR images were transferred to the neurosurgical navigation system. Following this strategy, after an average time of 3 hours, all data for presurgical planning and intraoperative navigation were available for the neurosurgeon.Our results show that MEG/MRI based functional neuronavigation can be used as a routine tool during daily neurosurgical practice.

Spontaneous mechanical and electrical activities of human calf musculature at rest assessed by repetitive single‐shot diffusion‐weighted MRI and simultaneous surface electromyography

Assessment of temporal and spatial relations between spontaneous mechanical activities in musculature (SMAM) at rest as revealed by diffusion‐weighted imaging (DWI) and electrical muscular activities in surface EMG (sEMG). Potential influences of static and radiofrequency magnetic fields on muscular activity on sEMG measurements at rest were examined systematically.

Magnetenzephalographie in der Neurochirurgie Ein Routineprotokoll zur präoperativen Planung und intraoperativen Navigation: Ein Routineprotokoll zur präoperativen Planung und intraoperativen Navigation

Zusammenfassung: Die Magnetenzephalographie (MEG) ermöglicht in Kombination mit der Magnetresonanztomographie (MRT) die Lokalisation und funktionelle Charakterisierung der Zentralregion. Aufgrund des großen apparativen und zeitlichen Aufwandes konnte sich dieses Verfahren bisher in der neurochirurgischen Routine nicht durchsetzen. Ziel der hier vorgestellten Arbeit war daher die Entwicklung eines Protokolls, welches die Integration funktioneller MEG-Daten in die Planung und Durchführung von neurochirurgischen Operationen als Routinemethode ermöglicht.Es wurden 45 Patienten mit Raumforderungen im Bereich der Zentralregion im MEG untersucht. Die somatosensorische Lokalisation erfolgte über die elektrische Stimulation des Nervus tibialis und des Nervus medianus. Für die motorische Lokalisation wurden von den Patienten Bewegungen des Zeigefingers durchgeführt. Die Ortskoordinaten wurden auf einen 3D-MRT-Datensatz übertragen und markiert. Abschließend erfolgte die Übertragung dieses markierten MRT-Datensatzes auf den Rechner des neurochirurgischen Navigationssystems. Unter Anwendung des hier vorgestellten Protokolls standen dem Neurochirurgen nach durchschnittlich drei Stunden alle relevanten Daten sowohl zur präoperativen Planung als auch zur intraoperativen Navigation zur Verfügung.Die Ergebnisse zeigen, dass die auf MEG und MRT basierende funktionelle Neuronavigation in der täglichen neurochirurgischen Routine eingesetzt werden kann.Abstract: The combination of magnetoencephalography (MEG) and magnetic resonance imaging (MRI) allows the localization and functional characterization of the somatosensory and motor cortex. However, this method is technically pretentious and time consuming. Therefore, functional imaging is still not established as routine procedure in neurosurgery. The aim of the presented study was the development of a protocol, which allows the integration of functional MEG data into presurgical planning and intraoperative navigation, as a routine method.Forty-five patients with intracranial mass lesions within the central region were examined by MEG. For the somatosensory localization, the median and tibial nerves were electrically stimulated. The motor cortex was localized by tapping of the index finger. The coordinates of the functional dipole source were projected onto a 3D MRI data-set. Finally, the marked MR images were transferred to the neurosurgical navigation system. Following this strategy, after an average time of 3 hours, all data for presurgical planning and intraoperative navigation were available for the neurosurgeon.Our results show that MEG/MRI based functional neuronavigation can be used as a routine tool during daily neurosurgical practice.The combination of magnetoencephalography (MEG) and magnetic resonance imaging (MRI) allows the localization and functional characterization of the somatosensory and motor cortex. However, this method is technically pretentious and time consuming. Therefore, functional imaging is still not established as routine procedure in neurosurgery. The aim of the presented study was the development of a protocol, which allows the integration of functional MEG data into presurgical planning and intraoperative navigation, as a routine method.Forty-five patients with intracranial mass lesions within the central region were examined by MEG. For the somatosensory localization, the median and tibial nerves were electrically stimulated. The motor cortex was localized by tapping of the index finger. The coordinates of the functional dipole source were projected onto a 3D MRI data-set. Finally, the marked MR images were transferred to the neurosurgical navigation system. Following this strategy, after an average time of 3 hours, all data for presurgical planning and intraoperative navigation were available for the neurosurgeon.Our results show that MEG/MRI based functional neuronavigation can be used as a routine tool during daily neurosurgical practice.