Amir Samii

Hannover Medical School, Hanover, Lower Saxony, Germany

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Publications (123)243.72 Total impact

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    ABSTRACT: Background: Music can elicit strong emotions and can be remembered in connection with these emotions even decades later. Yet, the brain correlates of episodic memory for highly emotional music compared with less emotional music have not been examined. We therefore used fMRI to investigate brain structures activated by emotional processing of short excerpts of film music successfully retrieved from episodic long-term memory. Methods: Eighteen non-musicians volunteers were exposed to 60 structurally similar pieces of film music of 10 s length with high arousal ratings and either less positive or very positive valence ratings. Two similar sets of 30 pieces were created. Each of these was presented to half of the participants during the encoding session outside of the scanner, while all stimuli were used during the second recognition session inside the MRI-scanner. During fMRI each stimulation period (10 s) was followed by a 20 s resting period during which participants pressed either the "old" or the "new" button to indicate whether they had heard the piece before. Results: Musical stimuli vs. silence activated the bilateral superior temporal gyrus, right insula, right middle frontal gyrus, bilateral medial frontal gyrus and the left anterior cerebellum. Old pieces led to activation in the left medial dorsal thalamus and left midbrain compared to new pieces. For recognized vs. not recognized old pieces a focused activation in the right inferior frontal gyrus and the left cerebellum was found. Positive pieces activated the left medial frontal gyrus, the left precuneus, the right superior frontal gyrus, the left posterior cingulate, the bilateral middle temporal gyrus, and the left thalamus compared to less positive pieces. Conclusion: Specific brain networks related to memory retrieval and emotional processing of symphonic film music were identified. The results imply that the valence of a music piece is important for memory performance and is recognized very fast.
    Frontiers in Psychology 01/2014; 5:114.
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    ABSTRACT: Objective The operative management of cystic vestibular schwannoma is more challenging. In the study we focus on the peculiarity of cystic vestibular schwannoma in terms of management and outcome. We evaluated a homogenous series of consecutive patients with cystic vestibular schwannomas, operated with similar technique and via the same surgical approach Methods The patients with vestibular schwannoma, who were operated at our center from 2000 to 2012, were retrospectively analyzed. Those having cystic vestibular schwannomas, recognized with the presence of cystic components both on the preoperative MRI images and intraoperatively, were included. Thirty seven consecutive patients matched the inclusive criteria. The whole pool of solid vestibular schwannomas with similar tumor extension was used as a control group. The facial nerve outcome is reported early after surgery and after one year follow up. Facial nerve palsy GI-III according to House-Brackmann grading system was considered favorable outcome. Facial nerve palsy GIV-VI was considered unfavorable. The surgical morbidity in the two groups were compared. A special point of interest was the correlation between the cyst pattern and outcome. Results Cystic vestibular schwannomas are associated with a worse early facial nerve outcome (unfavorable in 37.8% in cystic vestibular schwannoma compared to 17.5% in the solid variant). After one year follow-up, 8.1% of the cystic variant had unfavorable facial nerve outcome. Meanwhile 6.2% of the solid variant had unfavorable outcome. There was no statistically significant difference between both groups regarding the long term facial nerve outcome. The cystic variant had a higher postoperative morbidity rates especially hemorrhage (8.1%) in comparison to solid vestibular schwannoma of the same extension(1.7%).Hydrocephalus without significant hematoma is also significantly higher in the cystic type than the solid variant. Medially located thin walled cyst are related to worse facial nerve outcome. Conclusion Surgery of cystic vestibular schwannomas is associated with a higher morbidity rate and facial nerve dysfunction in comparison to the solid variant. Special attention is required during facial dissection allow functional preservation especially with tumors with medially located thin walled cysts. Meticulous hemostasis is also required to avoid postoperative hematoma. Close postoperative care is mandatory for early detection and prompt management of possible postoperative complications.
    World Neurosurgery 01/2014; · 1.77 Impact Factor
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    ABSTRACT: Object An extensive craniopharyngioma is a tumor that extends into multiple compartments (subarachnoid spaces) and attains a size larger than 4 cm. A wide spectrum of approaches and strategies has been used for resection of such craniopharyngiomas. In this report the authors focused on the feasibility and efficacy of microsurgical resection of extensive craniopharyngiomas using a frontolateral approach. Methods A retrospective analysis was performed on 16 patients with extensive craniopharyngiomas who underwent operations using a frontolateral approach at one institution. The preoperative and postoperative clinical and radiological data, as well as the operative videos, were reviewed. The main focus of the review was the extent of radical tumor removal, early postoperative outcome, and approach-related complications. Results Gross-total resection of craniopharyngioma was achieved in 14 (87.5%) of 16 cases. Early after surgery (within 3 months), 1 patient showed improvement in hormonal status, while in the remaining 15 patients it worsened. No major neurological morbidity was observed. Two patients experienced temporary psychotic disorders. Visual function improved in 6 patients and remained unchanged in 9. One patient experienced a new bitemporal hemianopsia. Three patients with features of short-term memory disturbances at presentation did show improvement after surgery. There were no deaths or significant approach-related morbidity in this patient series. Only 1 patient required revision surgery for a CSF leak. Conclusions The safe and simple frontolateral approach provides adequate access even to extensive craniopharyngiomas and enables their complete removal with a reasonable morbidity and approach-related complication rate.
    Journal of Neurosurgery 11/2013; · 3.15 Impact Factor
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    ABSTRACT: Intraoperative magnetic resonance imaging (iopMRI) actually has an important role in the surgery of brain tumors, especially gliomas and pituitary adenomas. The aim of our work was to describe the advantages and drawbacks of this tool for the surgical treatment of cervical intramedullary gliomas. We describe two explicative cases including the setup, positioning, and the complete workflow of the surgical approach with intraoperative imaging. Even if the configuration of iopMRI equipment was originally designed for cranial surgery, we have demonstrated the feasibility of cervical intramedullary glioma resection with the aid of high-field iopMRI. This tool was extremely useful to evaluate the extent of tumor removal and to obtain a higher resection rate, but still need some enhancement in the configuration of the headrest coil and surgical table to allow better patient positioning.
    Neurosurgical Review 11/2013; · 1.97 Impact Factor
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    ABSTRACT: Speech comprehension relies on auditory as well as visual information, and is enhanced in healthy subjects, when audiovisual information is present. Patients with schizophrenia have been reported to have problems regarding this audiovisual integration process, but little is known about which underlying neural processes are altered. Functional magnetic resonance imaging was performed in 15 schizophrenia patients and 15 healthy controls to study functional connectivity of Brocás area by means of a beta series correlation method during perception of audiovisually presented bisyllabic German nouns, in which audio and video either matched or did not match. Brocás area of schizophrenia patients showed stronger connectivity with supplementary motor cortex for incongruent trials whereas healthy controls connectivity was stronger for congruent trials. The right posterior superior temporal sulcus (RpSTS) area showed differences in connectivity for congruent and incongruent trials in healthy controls in contrast to schizophrenia patients where the connectivity was similar for both conditions. These smaller differences in connectivity in schizophrenia patients suggest a less adaptive processing of audiovisually congruent and incongruent speech. The findings imply that audiovisual integration problems in schizophrenia are associated with maladaptive connectivity of Broca's and RpSTS area in particular when confronted with incongruent stimuli. Results are discussed in light of recent audio visual speech perception models.
    Neuroscience 08/2013; · 3.12 Impact Factor
  • Clinical neurology and neurosurgery 07/2013; 115(7):1131–1133. · 1.30 Impact Factor
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    ABSTRACT: Image-guided neurosurgery, endoscopic-assisted neurosurgery and the keyhole approach are three important parts of minimally invasive neurosurgery and have played a significant role in treating skull base lesions. This study aimed to investigate the potential usefulness of coupling of the endoscope with the far lateral keyhole approach and image guidance at the ventral craniocervical junction in a cadaver model. We simulated far lateral keyhole approach bilaterally in five cadaveric head specimens (10 cranial hemispheres). Computed tomography-based image guidance was used for intraoperative navigation and for quantitative measurements. Skull base structures were observed using both an operating microscope and a rigid endoscope. The jugular tubercle and one-third of the occipital condyle were then drilled, and all specimens were observed under the microscope again. We measured and compared the exposure of the petroclivus area provided by the endoscope and by the operating microscope. Statistical analysis was performed by analysis of variance followed by the Student-Newman-Keuls test. With endoscope assistance and image guidance, it was possible to observe the deep ventral craniocervical junction structures through three nerve gaps (among facial-acoustical nerves and the lower cranial nerves) and structures normally obstructed by the jugular tubercle and occipital condyle in the far lateral keyhole approach. The surgical area exposed in the petroclival region was significantly improved using the 0° endoscope (1147.80 mm(2)) compared with the operating microscope ((756.28 ± 50.73) mm(2)). The far lateral retrocondylar keyhole approach, using both 0° and 30° endoscopes, provided an exposure area ((1147.80 ± 159.57) mm(2) and (1409.94 ± 155.18) mm(2), respectively) greater than that of the far lateral transcondylar transtubercular keyhole approach ((1066.26 ± 165.06) mm(2)) (P < 0.05). With the aid of the endoscope and image guidance, it is possible to approach the ventral craniocervical junction with the far lateral keyhole approach. The use of an angled-lens endoscope can significantly improve the exposure of the petroclival region without drilling the jugular tubercle and occipital condyle.
    Chinese medical journal 05/2013; 126(9):1707-13. · 0.90 Impact Factor
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    ABSTRACT: BACKGROUND:: Surgery of lesions of the petrous apex involving the inframeatal/infralabyrinthine area is challenging and related to high risk of complications. Various extensive skull base approaches have been utilized. OBJECTIVE:: To present and evaluate our experience with a new hearing preserving extension of the retrosigmoid approach to the inframeatal/infralabyrinthine area. METHODS:: The approach was used in three patients harboring lesions in the petrous apex with variable extension in the inframeatal/infralabyrinthine region. The surgical accessibility of the lesions offered by the approach, the completeness of tumor removal, and the outcome, in particular the functional outcome and complication rate, were assessed. RESULTS:: The tumor could be resected from the target area in all cases. No approach-related complications occurred. Serviceable hearing and normal facial nerve functions were preserved in all cases. CONCLUSION:: Our initial experience with the retrosigmoid inframeatal approach showed that it provides sufficient access to the area and offers the possibility of complete tumor removal. It allows for hearing and facial nerve functional preservation. The approach is safe and related to a very low complication rate.
    Neurosurgery 01/2013; · 2.53 Impact Factor
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    ABSTRACT: Parkinson's disease has been found to impair comprehension of complex sentences. Here we follow up on earlier findings that sentences describing two successive events in the form of "Before B, A" are understood worse by Parkinson patients than sentences in the form of "After A, B". Before-initial sentences express events in an order inconsistent with their actual order of occurrence and therefore require additional computations during comprehension. In a behavioral study we tested whether 28 German Parkinson patients reading 'before'- and 'after'-initial sentences correctly understood the sequence of events. A second functional magnetic resonance imaging study investigated 16 different patients who read sentences while in the scanner. The behavioral study revealed that 'before' sentences were misunderstood with regard to the temporal sequence of events in 53% (controls 6.5%). The imaging study demonstrated a functional network of the caudate nucleus, middle frontal gyrus, medial superior frontal gyrus, parietal lobule and inferior temporal gyrus. This network was dynamically modulated for 'before' compared to 'after' sentences in healthy controls but not in Parkinson patients. The current results suggest that the additional computations required for 'before' sentences are supported by a network with the caudate nucleus as a central element. This network was compromised in Parkinson patients. We propose that dysfunction of the caudate nucleus networks underlies Parkinson patients' difficulty in dealing with complex sentence structures.
    Neuropsychologia 05/2012; 50(8):1794-800. · 3.48 Impact Factor
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    ABSTRACT: Ganglion cysts (ganglia) are benign lesions of the soft tissue arising in the periarticular space. We present a 54-year-old woman with a 5-month history of headache and weakness of the tongue with deviation to the left side who had a rare extraneural intradural bilobate ganglion cyst of the atlanto-occipital joint compressing the hypoglossal nerve. An MRI showed a bilobate cystic lesion in the premedullary cistern on the left side at the level of the hypoglossal canal. This lesion was removed using a lateral suboccipital approach in the semi-sitting position with removal of the C1 hemiarch. The lesion proved to be a ganglion cyst on histopathology. Intracranial juxtafacet (ganglion and synovial) cysts compressing the hypoglossal nerve should be considered in the differential diagnosis with other lesions of this region. Although there was no recurrence at 30-month follow-up, there was no significant improvement of the tongue weakness. We describe our surgical strategy and discuss the pathogenesis of the cyst.
    Journal of Clinical Neuroscience 03/2012; 19(3):472-3. · 1.25 Impact Factor
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    ABSTRACT: Among the various introduced experimental traumatic brain injury models, there is a clear paucity of proper experimental polytrauma models. To overcome this experimental gap we introduced such a polytrauma model in the mouse including traumatic brain injury. Here, we report on the histopathological features of the brain, lung, kidney, spleen and liver. 20 male C57BL mice with a mean weight of 23 g were anesthetized with ketamine and xylazine. The anaesthetized animals were subjected to a controlled cortical impact (CCI) over the left parieto-temporal cortex using rounded-tip impounder for application of a standardized brain injury. Following fracture of the right femur using a guillotine, a volume-controlled hemorrhagic shock was induced. The control groups included animals with CCI only (n=20) and animals with femur fracture plus hemorrhagic shock without CCI (n=20). Subjects were sacrified at 96 h following trauma. Brain, lung, kidney, spleen and liver of the animals underwent histopathological examinations. The mortality rate at 96 h was 25% in the polytrauma group versus 10% in the control groups. Within the histopathological investigations, polytraumatized animals differ from those with a single trauma (traumatic brain injury or femur fracture with hemorrhagic shock) with various severity. The findings of this study show that such a polytrauma model can be standardized resulting in a reproducible damage. This model fulfills the requirements of a standardized animal model. It allows adequate analogies and inferences to the clinical situation of a polytrauma in humans.
    Experimental and toxicologic pathology: official journal of the Gesellschaft fur Toxikologische Pathologie 03/2012; 64(3):133-9. · 1.43 Impact Factor
  • Amir Samii, Venelin M Gerganov
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    ABSTRACT: Background The establishment of neuroendoscopy has been one of the major achievements in neurosurgery in the last 2 decades. The use of the endoscope increases efficacy and safety in each procedure. Methods The integration of endoscopy with other operating techniques or imaging technologies enhances the safety and reliability of the technique. Results The efficacy of the procedures, patient safety, and extent of resection have been increased by the integration of endoscopy with all of these sophisticated operative tools and imaging sources. Endoscopy has led to shortening of operative time and of the duration of hospital stay. Conclusions A dedicated endoscopic operating room should provide workflow optimization, ergonomic solutions, and highest safety standards for the patient.
    World Neurosurgery 02/2012; · 1.77 Impact Factor
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    ABSTRACT: An increasing number of patients with vestibular schwannomas (VSs) are being treated with radiosurgery. Treatment failure or secondary regrowth after radiosurgery, however, has been observed in 2%-9% of patients. In large tumors that compress the brainstem and in patients who experience rapid neurological deterioration, surgical removal is the only reasonable management option. The authors evaluated the relevance of previous radiosurgery for the outcome of surgery in a series of 28 patients with VS. The cohort was further subdivided into Group A (radiosurgery prior to surgery) and Group B (partial tumor removal followed by radiosurgery prior to current surgery). The functional and general outcomes in these 2 groups were compared with those in a control group (no previous treatment, matched characteristics). RESULTS There were 15 patients in Group A, 13 in Group B, and 30 in the control group. The indications for surgery were sustained tumor enlargement and progression of neurological symptoms in 12 patients, sustained tumor enlargement in 15 patients, and worsening of neurological symptoms without evidence of tumor growth in 1 patient. Total tumor removal was achieved in all patients in Groups A and B and in 96.7% of those in the control group. There were no deaths in any group. Although no significant differences in the neurological morbidity or complication rates after surgery were noted, the risk of new cranial nerve deficits and CSF leakage was highest in patients in Group B. Patients who underwent previous radiosurgical treatment (Groups A and B) tended to be at higher risk of developing postoperative hematomas in the tumor bed or cerebellum. The rate of facial nerve anatomical preservation was highest in those patients who were not treated previously (93.3%) and decreased to 86.7% in the patients in Group A and to 61.5% in those in Group B. Facial nerve function at follow-up was found to correlate to the previous treatment; excellent or good function was seen in 87% of the patients from the control group, 78% of those in Group A, and 68% of those in Group B. Complete microsurgical removal of VSs after failed radiosurgery is possible with an acceptable morbidity rate. The functional outcome, however, tends to be worse than in nontreated patients. Surgery after previous partial tumor removal and radiosurgery is most challenging and related to worse outcome.
    Journal of Neurosurgery 01/2012; 116(4):713-20. · 3.15 Impact Factor
  • 01/2012: pages 313-325;
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    ABSTRACT: Despite broad research in neurotrauma and shock, little is known on systemic inflammatory effects of the clinically most relevant combined polytrauma. Experimental investigation in an animal model may provide relevant insight for therapeutic strategies. We describe the effects of a combined injury with respect to lymphocyte population and cytokine activation. 45 male C57BL/6J mice (mean weight 27 g) were anesthetized with ketamine/xylazine. Animals were subjected to a weight drop closed traumatic brain injury (WD-TBI), a femoral fracture and hemorrhagic shock (FX-SH). Animals were subdivided into WD-TBI, FX-SH and combined trauma (CO-TX) groups. Subjects were sacrificed at 96 h. Blood was analysed for cytokines and by flow cytometry for lymphocyte populations. Mortality was 8%, 13% and 47% for FX-SH, WD-TBI and CO-TX groups (P < 0.05). TNFα (11/13/139 for FX-SH/WD-TBI/CO-TX; P < 0.05), CCL2 (78/96/227; P < 0.05) and IL-6 (16/48/281; P = 0.05) showed significant increases in the CO-TX group. Lymphocyte populations results for FX-SH, WD-TBI and CO-TX were: CD-4 (31/21/22; P = n.s.), CD-8 (7/28/34, P < 0.05), CD-4-CD-8 (11/12/18; P = n.s.), CD-56 (36/7/8; P < 0.05). This study shows that a combination of closed TBI and femur-fracture/ shock results in an increase of the humoral inflammation. More attention to combined injury models in inflammation research is indicated.
    Mediators of Inflammation 01/2012; 2012:136020. · 3.88 Impact Factor
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    Samii M, Samii A, Gerganov V
    Indian journal of neurosurgery. 01/2012; 1:9-13.
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    ABSTRACT: The reliable preoperative visualization of facial nerve location in relation to vestibular schwannoma (VS) would allow surgeons to plan tumor removal accordingly and may increase the safety of surgery. In this prospective study, the authors attempted to validate the reliability of facial nerve diffusion tensor (DT) imaging-based fiber tracking in a series of patients with large VSs. Furthermore, the authors evaluated the potential of this visualization technique to predict the morphological shape of the facial nerve (tumor compression-related flattening of the nerve). Diffusion tensor imaging and anatomical images (constructive interference in steady state) were acquired in a series of 22 consecutive patients with large VSs and postprocessed with navigational software to obtain facial nerve fiber tracking. The location of the cerebellopontine angle (CPA) part of the nerve in relation to the tumor was recorded during surgery by the surgeon, who was blinded to the results of the fiber tracking. A correlative analysis was performed of the imaging-based location of the nerve compared with its in situ position in relation to the VS. Fibers corresponding to the anatomical location and course of the facial nerve from the brainstem to the internal auditory meatus were identified with the DT imaging-based fiber tracking technique in all 22 cases. The location of the CPA segment of the facial nerve in relation to the VS determined during surgery corresponded to the location of the fibers, predicted by the DT imaging-based fiber tracking, in 20 (90.9%) of the 22 patients. No DT imaging-based fiber tracking correlates were found with the 2 morphological types of the nerve (compact or flat). The current study of patients with large VSs has shown that the position of the facial nerve in relation to the tumor can be predicted reliably (in 91%) using DT imaging-based fiber tracking. These are preliminary results that need further verification in a larger series.
    Journal of Neurosurgery 08/2011; 115(6):1087-93. · 3.15 Impact Factor
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    ABSTRACT: For postoperative CSF-fistula prevention a better understanding of its origins and risk factors is necessary. To identify the role of the tumor growth for the risk to develop CSF-fistula we performed a retrospective analysis. 519 patients between the years 2000 and 2007 had a retrosigmoidal surgical removal of vestibular schwannoma in a standardized procedure. 22 CSF-fistula-patients were chosen for evaluation. 78 patients were randomly selected as control group in four equally sized cohorts: male/female with small/large tumors. Preoperative CT-scans were analyzed regarding IAC-length, diameter of the IAC porus (IAP), tumor size and pneumatization of the posterior wall (PW) of the IAC. The mean length of the IAC was 1.2 cm, SD 0.17. There was a significant difference between the diameter of the IAP in cases of small tumors and those of large tumors. Patients with small tumors also showed a larger fraction with visible pneumatization of the PW (34.88%) in the CT-scan than patients with large tumors (24.07%). There is a positive correlation between tumor grade and diameter of the IAP. At the same time there is an inverse correlation between tumor grade and pneumatization of the PW. Widening of the IAC by tumor growth may leads to obliteration of air cells in the PW and therefore can be protective concerning CSF-fistula. At the same time patients with small tumors and a visible pneumatization in the PW must be expected to have a higher risk of CSF-fistula.
    Clinical neurology and neurosurgery 08/2011; 113(9):746-51. · 1.30 Impact Factor
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    ABSTRACT: Some previous functional magnetic resonance imaging (fMRI) studies have revealed increased activation in amyotrophic lateral sclerosis (ALS) patients but longitudinal data on such activation changes are lacking. To assess the time course of changes in fMRI patterns and their potential contribution to the understanding of ALS pathophysiology, we, therefore, investigated a total of 22 patients with ALS and matched control participants while they performed a blocked motor task. Patients were assigned to three groups according to whether they had no (MRC grade 5), mild (MRC 4), or marked (MRC 3) weakness of the examined right hand. Significant activations were seen in primary motor and premotor cortex, somatosensory cortex, supplementary motor area and subcortical areas in all groups. The size of the activated area in the contralateral sensorimotor cortex was increased to a similar degree in all three ALS groups compared to control participants irrespective of weakness on clinical examination. Whereas movement related signal change and beta weights extracted from the activated cluster were unchanged relative to controls in ALS patients with no weakness, a marked decrease of these parameters was seen in patients with weakness. Two distinct stages of neuroplastic changes could be identified in ALS (first: increase of the activated area in contralateral sensorimotor cortex; second: reduction of signal change and beta weights with increasing weakness). We interpret the increase of the activated area as a result of decreased intracortical inhibition and the reduction of movement related signal change and beta weights as a consequence of loss of upper motor neurons.
    Human Brain Mapping 05/2011; 32(5):750-8. · 6.88 Impact Factor
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    ABSTRACT: Writer's cramp (WC) is characterized by excessive cocontractions of agonist and antagonist hand and forearm muscles during writing. Changes in functional magnetic resonance imaging activation patterns in such conditions can be ambiguous as they might either reflect some aspect of the primary pathophysiological mechanism or, alternatively, may be the result of adaptive actions during task execution. To circumvent this problem, we examined WC patients during rest, i.e., without a task, using independent component analysis (ICA) applied to the blood oxygen level-dependent time series. Functionally connected brain networks during rest were defined by ICA to assess differences between WC patients (n = 16) and healthy controls (n = 16). Analysis was carried out using FMRIB's Software Library. Two functional networks showed between-group differences, the sensorimotor network and the default-mode network. In WC patients, the connectivity was reduced in the left postcentral area and increased in basal ganglia in contrast to healthy controls. These changes were not reversed after treatment with botulinum toxin. In line with other studies, the results show a dysfunction in cortico-subcortical circuits in WC involving somatosensory cortex, areas interfacing the sensory and motor systems, and putamen contralateral to symptomatic hand.
    Human Brain Mapping 04/2011; 33(4):840-8. · 6.88 Impact Factor

Publication Stats

1k Citations
243.72 Total Impact Points

Institutions

  • 2003–2013
    • Hannover Medical School
      • Trauma Department
      Hanover, Lower Saxony, Germany
    • International Neuroscience Institute
      Hanover, Lower Saxony, Germany
    • Children's Hospital of Michigan
      Detroit, Michigan, United States
  • 2011–2012
    • Universität zu Lübeck
      Lübeck Hansestadt, Schleswig-Holstein, Germany
  • 2004–2011
    • International Neuroscience Institute Hannover
      Hanover, Lower Saxony, Germany
  • 2003–2011
    • Otto-von-Guericke-Universität Magdeburg
      • Faculty of Medicine and University Clinic Magdeburg
      Magdeburg, Saxony-Anhalt, Germany
  • 2010
    • Xuanwu hospital
      Peping, Beijing, China
  • 2009
    • Insight Institute of Neurosurgery and Neuroscience
      Flint, Michigan, United States
  • 2008
    • Barrow Neurological Institute
      Phoenix, Arizona, United States
  • 2007
    • St. Joseph Medical Center
      Houston, Texas, United States
  • 2006–2007
    • University of Naples Federico II
      • Department of Neuroscience and Reproductive and Odontostomatological Sciences
      Napoli, Campania, Italy
  • 2005
    • The Jikei University School of Medicine
      • Department of Neurosurgery
      Tokyo, Tokyo-to, Japan
  • 1998–2000
    • Humboldt-Universität zu Berlin
      Berlín, Berlin, Germany