Brain topography
-
Over the last 20 years, a body of techniques known as high resolution EEG has allowed precise estimation of cortical activity from non-invasive EEG measurements. The availability of cortical waveforms from non-invasive EEG recordings allows to have not only the level of activation within a single region of interest (ROI) during a particular task, but also to estimate the causal relationships among activities of several cortical regions. However, interpreting resulting connectivity patterns is still an open issue, due to the difficulty to provide an objective measure of their properties across different subjects or groups. ⋯ For both the experiments, the main question is whether the "architecture" of the functional connectivity networks obtained could show properties that are different in the two groups or in the two tasks. All the functional connectivity networks gathered in the two experiments showed ordered properties and significant differences from "random" networks having the same characteristic sizes. The proposed approach, based on the use of indexes derived from graph theory, can apply to cerebral connectivity patterns estimated not only from the EEG signals but also from different brain imaging methods.
-
Comparative Study
Cortical characterization and inter-dipole distance between unilateral median versus ulnar nerve stimulation of both hands in MEG.
Contralateral somatosensory evoked fields (SEF) by whole head MEG after unilateral median and ulnar nerve stimulation of both hands were studied in 10 healthy right-handed subjects. Major parameters describing cortical activity were examined to discriminate median and ulnar nerve evoked responses. Somatic sensitivity showed high similarity in the 4 study conditions for both hand and nerve. ⋯ Especially the dipole distance between median and ulnar nerve on the cortex was computed accurately for the first time in MEG. Little is known however of the cortical responses in chronic pain patients and the parameter(s) that may change in an individual patient or a group. These results provide precise basis for further evaluating cortical changes in functional disorders and disease sequelae related to median and ulnar nerves.
-
An integrated model for magnetoencephalography (MEG) and functional Magnetic Resonance Imaging (fMRI) is proposed. In the model, the neural activity is related to the Post Synaptic Potentials (PSPs) which is common link between MEG and fMRI. Each PSP is modeled by the direction and strength of its current flow which are treated as random variables. ⋯ In addition, the model shows that the crosstalk from neural activities of the adjacent voxels in fMRI may result in the detection of activations in these voxels that contain no neural activities. The proposed model is instrumental in evaluating and comparing different analysis methods of MEG and fMRI. It is also useful in characterizing the upcoming combined methods for simultaneous analysis of MEG and fMRI.
-
Comparative Study
Scalp field potentials of human pain: spatial effects and temporal relation in finger stimulation.
In the present study, the spatial extent and temporo-spatial correlations of the human brain responses were investigated by electrically stimulating thumb (D1) and little finger (D5) under painful and non-painful intensity levels. High-density (124-ch) somatosensory evoked potentials (SEPs) were recorded (-50 to +450 ms) from 15 healthy male volunteers. Early (0-50 ms), and late phases (150-450 ms) of the responses were analyzed. ⋯ For the late phase, the AM potentials at N2 correlated with that of P2 for both D1 and D5 under painful stimulation. The focal effects in FA of contralateral early potential indicates a shallow dipole in the primary somatosensory area of SI, while the large spatial extent in AM indicates a deep dipole of the putative cingulum activation under painful stimulation. No correlation between early and late activities implied that both activations are operated independently at the early SI and late cingulate processing of evoked pain.
-
Comparative Study
Topographic analysis of painful laser and sural nerve electrical evoked potentials.
A quantitative scalp topographic pattern analysis was used to compare evoked potentials elicited by painful laser (LEP) and electrical stimulation of the sural nerve (snSEP) in 22 healthy adults. The snSEP and LEP were separated into stable periods (consecutive time points having the same topographic pattern). The topographic pattern is dependent upon the number, location, orientation and relative magnitudes of the brain areas active at that time (source configuration). ⋯ These findings have important implications for the choice of evoking stimulus in investigations of pain processing in humans. For example, the sural nerve electrical stimulus will be preferred over the laser in studies of the anterior cingulate's role in cognitive processes related to pain, such as orienting attention, and/or in studies involving cognitive tasks that require the presentation of a large number of painful stimuli. The LEP N1 and N2 peaks, on the other hand, will be preferred in studies of the parietal operculum's role in pain sensation.