Biomedical subjects

M J Kajola

Publications and source records attributed to M J Kajola.

2 recordsLinked to original sources

PubMed1995

Characterizing the local oscillatory content of spontaneous cortical activity during mental imagery.

We report on the determination of detailed spectra for simultaneously active sources of spontaneous neuronal activity in humans directly from data recorded with a whole-scalp 122-channel magnetometer array. Subjects rested with eyes open and performed two contrasting mental imagery tasks: the imagination of the self-performance of a motor activity and the silent generation of a chain of words. A novel analysis technique, frequency-domain signal-space projection (FDSSP) was utilized to determine the temporal and spectral characteristics of spontaneous brain activity at specific cortical sites. Although intersubject differences were significant, spectra for individual subjects contained task-dependent features which were reproducible over successive 20-s epochs. This result supports the concept of multiple sources of spontaneous cortical activity and suggests that detailed spectra of localized oscillatory activity obtained non-invasively with magnetoencephalographic arrays may provide a useful characterization of cortical involvement in mental imagery.

Algorithms↗

PubMed1993

Sampling theory for neuromagnetic detector arrays.

The sampling theorem for wave-number-limited multivariable functions is applied to the problem of neuromagnetic field mapping. The wave-number spectrum and other relevant properties of these fields are estimated. A theory is derived for reconstructing neuromagnetic fields from measurements using sensor arrays which sample either the field component Bz perpendicular to the planar grid of measurement points, or the two components delta Bz/delta x and delta Bz/delta y of its gradient in the xy plane. The maximum sensor spacing consistent with a unique reconstruction is determined for both cases. It is shown that, when two orthogonal components of the gradient are measured at every site of the measurement grid, the density of these sensor-pair units can be reduced, without risk of aliasing, to half of what is necessary for single-channel sensors in an array sampling Bz alone. Thus the planar and axial gradiometer arrays are equivalent in the sampling sense provided that the number of independent measurements per unit area is equal.

Brain Mapping↗