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Electrical impedance tomography (EIT) allows for the reconstruction of internal conductivity from surface measurements. A change in conductivity occurs as ion channels open during neural activity, making EIT a potential tool for functional brain imaging. EIT images can have >10 000 voxels, which means statistical analysis of such images presents a substantial multiple testing problem. One way to optimally correct for these issues and still maintain the flexibility of complicated experimental designs is to use random field theory. This parametric method estimates the distribution of peaks one would expect by chance in a smooth random field of a given size. Random field theory has been used in several other neuroimaging techniques but never validated for EIT images of fast neural activity, such validation can be achieved using non-parametric techniques. Both parametric and non-parametric techniques were used to analyze a set of 22 images collected from 8 rats. Significant group activations were detected using both techniques (corrected p

Background: Congenital bilateral perisylvian syndrome (CBPS) is characterised by bilateral perisylvian polymicrogyria and suprabulbar paresis. Mild tetraparesis, cognitive impairment, and epilepsy are frequently associated. Sensory deficits are surprisingly rare, even though polymicrogyria often extends to auditory and sensorimotor cortex. Objectives: To study the sensorimotor and auditory cortex function and location in CBPS patients. Methods: We mapped the sensory and motor cortex function onto brain magnetic resonance images in six CBPS patients and seven control subjects using sources of somatosensory and auditory evoked magnetic fields, and of rhythmic magnetoencephalographic (MEG) activity phase-locked to surface electromyogram (EMG) during voluntary hand muscle contraction. Results: MEG-EMG coherence in CBPS patients varied from normal (if normal central sulcus anatomy) to absent, and could occur at abnormally low frequency. Coherent MEG activity was generated at the central sulcus or in the polymicrogyric frontoparietal cortex. Somatosensory and auditory evoked responses were preserved and also originated within the polymicrogyric cortex, but the locations of some source components could be grossly shifted. Conclusion: Plastic changes of sensory and motor cortex location suggest disturbed cortex organisation in CBPS patients. Because the polymicrogyric cortex of CBPS patients may embed normal functions in unexpected locations, functional mapping should be considered before brain surgery.

Objective: Intraoperative localisation of the sensorimotor cortex using the phase reversal of somatosensory evoked potentials (SEPs) is an essential tool for surgery in and around the perirolandic gyri, but unsuccessful and perplexing results have been reported. This study examines the effect of tumour masses on the waveform characteristics and feasibility of SEP compared with functional neuronavigation and electrical motor cortex mapping. Methods: In 230 patients with tumours of the sensorimotor region the SEP phase reversal of N20-P20 was recorded from the exposed cortex using a subdural grid or strip electrode. In one subgroup of 80 patients functional neuronavigation was performed with motor and sensory magnetic source imaging and in one subgroup of 40 patients the motor cortex hand area was localised by electrical stimulation mapping. Results: The intraoperative SEP method was successful in 92% of all patients, it could be shown that the success rate rather depended on the location of the lesion than on preoperative neurological deficits. In 13% of the patients with postcentral tumours no N20-P20 phase reversal was recorded but characteristic polyphasic and high amplitude waves at 25 ms and later made the identification of the postcentral gyrus possible nevertheless. Electrical mapping of the motor cortex took up to 30 minutes until a clear result was obtained. It was successful in 37 patients, but failed in three patients with precentral and central lesions. Functional neuronavigation indicating the tumour margins and the motor and sensory evoked fields was possible in all patients. Conclusion: The SEP phase reversal of N20-P20 is a simple and reliable technique, but the success rate is much lower in large central and postcentral tumours. With the use of polyphasic late waveforms the sensorimotor cortex may be localised. By contrast with motor electrical mapping it is less time consuming. Functional neuronavigation is a desirable tool for both preoperative surgical planning and intraoperative use during surgery on perirolandic tumours, but compensation for brain shift, accuracy, and cost effectiveness are still a matter for discussion.

Digital EEG technology has facilitated the recording of fast activity above 50 Hz, but previous work carried out in this field is, commonly, no longer referred to in the literature. This paper presents a summary of our experience in experimental epilepsy when frequencies above 100 Hz were recorded. It was shown that conventional recordings (1–70 Hz) do not correlate with the onset of clinical seizures and can actually lead to misleading neurophysiologic conclusions. Ultrafast activity (100–1500 Hz), on the other hand, showed excellent correlation with clinical behavior and pointed to the low brainstem for the origin of nonfocal tonic-clonic seizures. In the animal analogue of absence seizures the cortex, including cingulate gyrus, thalamus, and cerebellum, showed greater involvement than other brain structures. Ultrafast activity has a very limited electrical field, and evoked responses remain restricted to the corresponding sensory pathways. Focal penicillin administration led not only to spike generation but also to associated ultrafast frequency bursts in that area. It appears likely that ultrafast burst activity may be a better marker for focal cortical epileptogenesis than spikes or sharp waves, which can be transmitted from a distance.

Objective: To assess the clinical value of magnetoencephalography (MEG) in localising the primary hand motor area and evaluating cortical distortion of the sensorimotor cortices in patients with intracerebral tumour. Methods: 10 normal volunteers (controls) and 14 patients with an intracerebral tumour located around the central region were studied. Somatosensory evoked magnetic fields (SEFs) following median nerve stimulation, and movement related cerebral magnetic fields (MRCFs) following index finger extension, were measured in all subjects and analysed by the equivalent current dipole (ECD) method to ascertain the neuronal sources of the primary sensory and motor components (N20m and MF, respectively). These ECD locations were defined as the primary hand sensory and motor areas and the positional relations between these two functional areas in controls and patients were investigated. Results: The standard range of ECD locations of MF to N20m was determined in controls. In 11 of the 14 patients, MRCFs could identify the primary motor hand area. ECD locations of MF were significantly closer to the N20m in the medial-lateral direction in patients than in controls. In patients with a tumour located below the sensorimotor hand area, relative ECD locations of MF to N20m moved anteriorly over the standard range determined in the control subjects. These MEG findings correlated well with radiological tumour locations. The mean estimated ECD strength of MF was significantly lower in patients than in controls. Conclusions: MRCF was useful in localising the primary motor hand area in patients with intracerebral tumour. The relative ECD locations of MF to N20m describe the anatomical distortion of the sensorimotor cortex.

Objectives: Subcortical lesions in the sensorimotor strip are often considered to be inoperable. The purpose of this study was to evaluate the usefulness of a combined approach for surgery in this region, aided by a robotic neuronavigation system under electrophysiological control. Methods: In a prospective study on 10 patients, space occupying lesions in the sensorimotor central area were removed using the Surgiscope® robotic navigation system and the Nicolet Viking IV® electrophysiological system. Results: Precise tumour localisation with the neuronavigation system and the information on the patient's cortical motor distribution obtained by bipolar cortical stimulation led to postoperative improvement in motor function in all but one patient. Seven of the patients had focal, defined pathology (four metastases; two cavernoma; one aspergilloma). Conclusion: Due to the implementation of two recent technologies, surgery of lesions in the subcortical sensorimotor region can be performed with greater confidence.

OBJECTIVES: Functional reorganisation of the motor or sensory cortex has been demonstrated in animals after section of mixed peripheral nerves. Here functional changes in the motor cortex specifically after peripheral motor denervation in humans are investigated. METHODS: Functional MRI (fMRI) was used to study brain activation during a finger flexion-extension task in patients with a late onset, acquired pure motor neuropathy (n=6), contrasting results with those from patients with pure sensory neuropathies (n=4) or healthy controls (n=7). RESULTS: Increases in the extent of activation in the motor cortex both ipsilateral and contralateral to the hand moved were found in the patients with motor neuropathy. The neuroanatomical localisation of the mixed contralateral sensorimotor cortex activation volume was more posterior for the patients with motor neuropathy than for the healthy controls (mean difference, 12 mm, p