Gross electrocortical activity as a linear wave phenomenon with variable temporal damping, regulated by ascending catecholamine neurones

A quantitative population model of whisker barrels: re-examining the Wilson-Cowan equations

Beginning from a biologically based integrate and fire model of a rat whisker barrel, we employ semirigorous techniques to reduce the system to a simple set of equations, similar to the Wilson-Cowan equations, while retaining the ability for both qualitative and quantitative comparisons with the biological system. This is made possible through the clarification of three distinct measures of population activity: voltage, firing rate, and a new term called synaptic drive. The model is activated by prerecorded neural activity obtained from thalamic "barreloid" neurons in response to whisker stimuli. Output is produced in the form of population PSTHs, one each corresponding to activity of spiny (excitatory) and smooth (inhibitory) barrel neurons, which is quantitatively comparable to PSTHs from electrophysiologically studied regular-spike and fast-spike neurons. Through further analysis, the model yields novel physiological predictions not readily apparent from the full model or from experimental studies.

Simulation of electrocortical waves

We report simulations of the electrocorticogram of the cat and human, based on estimates of fibre range, fibre density, axonal and dendritic delays, and cortical synaptic density. The long-range cortical connections of real cortex were simplified to couplings of symmetric density, decreasing in density with range, on a closed (toroidal) surface. Non-specific cortical activation was modelled as a diffuse global input and specific sensory input as a localised white noise input. Spectral properties of output included peak densities at the frequencies of the major cerebral rhythms, a '1/f' spectral envelope and 'shift to the right' with increasing total power as non-specific activation increased. Steady-state travelling waves with a velocity of 5-7 m/s (human) and < 1 m/s (cat) were produced. Frequency/wavenumber analysis revealed an additional class of activity with wavenumbers independent of temporal frequency. All these findings accord qualitatively and quantitatively with existing physiological results. Global resonant modes were not prominent, but the simulations obey a restricted case of the analytical results of Nunez (1994). Wave/pulse relations resemble the findings of Freeman (1975).

Active microwave computed brain tomography: the response to a challenge

The potential application of active microwave techniques to brain imaging is studied by numerical simulations and experimentally using a recently developed cylindrical microwave scanner. The potential advantages and limitations of this method in static and dynamic brain imaging are presented and compared with other imaging techniques.

Time and tiles on the brain

Both the quasicrystalline appearance of mammalian cerebral cortex and the quasiperiodicity of mammalian cerebral compound field potentials (EEG/ERBP) have long been noted. A recent experiment claims to show the eigenvalue spectrum of a quasiperiodic tiling of coupled oscillators in the plane; and this spectrum of resonant frequencies has some analogies with that of mammalian EEG/ERBP. Concurrently, Connectionist literature now admits the significance of internally generated network rhythmicity in Non-Lipschitzian neurodynamics. It may be time to test the hypotheses of: (a) quasi-crystalline icosahedral symmetry of neocortical architectonics and (b) some fractal characteristics of EEG/ERBP under behavioral conditions.