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  • Awake stereotactic biopsy of brain stem lesions: technique and results.

    26 April 2018

    BACKGROUND: Brain stem lesions are a heterogenous pathological group. In adults, pre-operative radiological diagnoses prove to be wrong in 10 to 20% of cases. It is therefore imperative to have a tissue diagnosis for appropriate therapeutic measures. Unless these lesions have a sizeable exophytic component, open biopsy and/or resection is marred by low diagnostic yield and prohibitive mortality/morbidity rates. METHODS: We describe our experience with awake stereotactic biopsy of brain stem lesions. Keeping the patient awake and monitoring clinically during the procedure allows us to make necessary changes in the trajectory of the biopsy probe to minimize the morbidity. A series of 13 brain stem lesions were stereotactically biopsied using CT guidance. Seven had midbrain lesions; four had pontine and two had Ponto-medullary lesions. A frontal, pre-coronal, transcortical trajectory was used in all patients. FINDINGS: Histological diagnosis was established in all but one patient. There was no procedural mortality, and morbidity was minimal and temporary, occurring in three patients. CONCLUSION: Awake stereotactic biopsy is a safe technique when combined with clinical monitoring.

  • The periaqueductal grey area and control of blood pressure in neurodegeneration.

    30 April 2018

    The periaqueductal/periventricular grey area (PAG/PVG) is a midbrain nucleus with an important role in pain signalling and autonomic control. We present the case of an initially hypertensive man who developed a presumed neurodegenerative disorder over a decade, characterised by progressive right-sided chronic pain, extra-pyramidal symptoms and autonomic dysfunction including postural hypotension, sleep apnoea, and bladder instability. He underwent a variety of treatments for his symptoms, including deep brain stimulation (DBS) of the PAG/PVG. 24-h blood pressure monitoring was carried out 1 and 5 years after implantation. Although the DBS initially produced a significant reduction in blood pressure, the effect was significantly reversed when the same tests were repeated 5 years after surgery. This may imply a functional involvement of the PAG/PVG in the neurodegenerative process.

  • Ready for action: a role for the human midbrain in responding to infant vocalizations.

    14 May 2018

    Infant vocalizations are among the most biologically salient sounds in the environment and can draw the listener to the infant rapidly in both times of distress and joy. A region of the midbrain, the periaqueductal gray (PAG), has long been implicated in the control of urgent, survival-related behaviours. To test for PAG involvement in the processing of infant vocalizations, we recorded local field potentials from macroelectrodes implanted in this region in four adults who had undergone deep brain stimulation. We found a significant difference occurring as early as 49 ms after hearing a sound in activity recorded from the PAG in response to infant vocalizations compared with constructed control sounds and adult and animal affective vocalizations. This difference was not present in recordings from thalamic electrodes implanted in three of the patients. Time frequency analyses revealed distinct patterns of activity in the PAG for infant vocalisations, constructed control sounds and adult and animal vocalisations. These results suggest that human infant vocalizations can be discriminated from other emotional or acoustically similar sounds early in the auditory pathway. We propose that this specific, rapid activity in response to infant vocalizations may reflect the initiation of a state of heightened alertness necessary to instigate protective caregiving.

  • Human periventricular grey somatosensory evoked potentials suggest rostrocaudally inverted somatotopy.

    10 May 2018

    BACKGROUND: Somatosensory homunculi have been demonstrated in primary somatosensory cortex and ventral posterior thalamus but not periaqueductal and periventricular grey matter (PAVG), a therapeutic target for deep brain stimulation (DBS) in chronic pain. AIMS: The study is an investigation of somatotopic representation in PAVG and assessment for a somatosensory homunculus. METHODS: Five human subjects were investigated using electrical somatosensory stimulation and deep brain macroelectrode recording. DBS were implanted in the contralateral PAVG. Cutaneous arm, leg and face regions were stimulated while event-related potentials were recorded from deep brain electrodes. Electrode contact positions were mapped using MRI and brain atlas information. RESULTS: Monopolar P1 somatosensory evoked potential amplitudes were highest and onset latencies shortest in contralateral caudal PAVG with facial stimulation and rostral with leg stimulation, in agreement with reported subjective sensation during intra-operative electrode advancement. CONCLUSIONS: A rostrocaudally inverted somatosensory homunculus exists in the human PAVG region. Objective human evidence of PAVG somatotopy increases understanding of a brainstem region important to pain and autonomic control that is a clinical target for both pharmacological and neurosurgical therapies. Such knowledge may assist DBS target localisation for neuropathic pain syndromes related to particular body regions like brachial plexopathies, anaesthesia dolorosa and phantom limb pain.

  • . Intra-axial Brain Tumors: Functional Tractography, Diffusion Tensor Imaging, Intraoperative Integration of Modalities, Neuronavigation

    27 October 2017

    Take it with you anywhere! Access the full text, downloadable image library, video clips, and more at

  • Complementary roles of different oscillatory activities in the subthalamic nucleus in coding motor effort in Parkinsonism.

    26 April 2018

    The basal ganglia may play an important role in the control of motor scaling or effort. Recently local field potential (LFP) recordings from patients with deep brain stimulation electrodes in the basal ganglia have suggested that local increases in the synchronisation of neurons in the gamma frequency band may correlate with force or effort. Whether this feature uniquely codes for effort and whether such a coding mechanism holds true over a range of efforts is unclear. Here we investigated the relationship between frequency-specific oscillatory activities in the subthalamic nucleus (STN) and manual grips made with different efforts. The latter were self-rated using the 10 level Borg scale ranging from 0 (no effort) to 10 (maximal effort). STN LFP activities were recorded in patients with Parkinson's Disease (PD) who had undergone functional surgery. Patients were studied while motor performance was improved by dopaminergic medication. In line with previous studies we observed power increase in the theta/alpha band (4-12 Hz), power suppression in the beta band (13-30 Hz) and power increase in the gamma band (55-90 Hz) and high frequency band (101-375 Hz) during voluntary grips. Beta suppression deepened, and then reached a floor level as effort increased. Conversely, gamma and high frequency power increases were enhanced during grips made with greater effort. Multiple regression models incorporating the four different spectral changes confirmed that the modulation of power in the beta band was the only independent predictor of effort during grips made with efforts rated <5. In contrast, increases in gamma band activity were the only independent predictor of effort during grips made with efforts ≥5. Accordingly, the difference between power changes in the gamma and beta bands correlated with effort across all effort levels. These findings suggest complementary roles for changes in beta and gamma band activities in the STN in motor effort coding. The latter function is thought to be impaired in untreated PD where task-related reactivity in these two bands is deficient.

  • Landmark Papers in Neurosurgery

    27 October 2017

    This book provides a detailed summary of the most important trials and studies in neurosurgery, allowing the reader to rapidly extract the key results of all major trials.

  • DBS for Pleasure

    27 October 2017

    This book is intended to serve as both a starting point for readers new to the field, and as a reference for more experienced graduate students and scientists from fields such as neuroscience, psychology, psychiatry, neurology, and ...