Subdural to subgaleal EEG signal transmission: the role of distance, leakage and insulating affectors.

OBJECTIVE: To estimate the area of cortex affecting the extracranial EEG signal. METHODS: The coherence between intra- and extracranial EEG channels were evaluated on at least 10 min of spontaneous, awake data from seven patients admitted for epilepsy surgery work up. RESULTS: Cortical electrodes showed significant extracranial coherent signals in an area of approximately 150 cm(2) although the field of vision was probably only 31 cm(2) based on spatial averaging of intracranial channels taking into account the influence of the craniotomy and the silastic membrane of intracranial grids. Selecting the best cortical channels, it was possible to increase the coherence values compared to the single intracranial channel with highest coherence. The coherence seemed to increase linearly with an accumulation area up to 31 cm(2), where 50% of the maximal coherence was obtained accumulating from only 2 cm(2) (corresponding to one channel), and 75% when accumulating from 16 cm(2). CONCLUSION: The skull is an all frequency spatial averager but dominantly high frequency signal attenuator. SIGNIFICANCE: An empirical assessment of the actual area of cerebral sources generating the extracranial EEG provides better opportunities for clinical electroencephalographers to determine the location of origin of particular patterns in the EEG.

Quantitative immunohistochemistry of fluorescence labelled probes using low-cost software.

This paper describes simple procedures to process digital images in quantitative immunofluorescence microscopy. Monoclonal antibodies directed against the sarcoplasmic myosin heavy chain isoforms and against laminin, located on the basement membranes, were applied to sections of human skeletal muscle. The localisation and staining intensity of a fluorescent secondary antibody were recorded using an indirect histochemical method. The digitised images were pre-processed and the luminosities of appropriate structures were determined using existing tools in the widely used image processing software Photoshop from Adobe. Procedures to obtain a quantitative measure for the specific fluorescence signal (the background corrected fluorescence in the object) were developed. In addition, antibody binding to individual cells could be quantified whether these cells are well separated or not. The relation between the specific fluorescence signal and the dilution factor of the primary antibody could be measured to determine a suitable concentration of the antibody for incubation of the sections. The potential fading of the fluorescence signal with time and prolonged exposure to light from the microscope was explored and analysed. With the tools described in the present report it is thus possible also to optimize the topical immunohistochemical protocol in order to quantify the fluorescence signal.