EEG spectrum components in verbal task solving

Abstracts 7th IOP Scientific Meeting /International curves should all be similar. Our results indicate that this is the case at high temporal frequencies (>4 Hz), but not at low temporal frequencies. The post-adaptation sensitivity functions for test patterns with temporal frequencies of 8 and 16 Hz were bandpass, with maximum adaptation near 12 Hz, and showed evidence of beat-specific adaptation. For ~-HZ test patterns the sensitivity functions were lowpass, adaptation declining above 20 Hz, but there was no beat-specific adaptation. The bimodal shape of the CSF and the results of the adaptation experiments suggest that two processes mediate the detection of second-order motion stimuli over complementary parts of the temporal frequency range. The results are consistent with the hypothesis that fast second-order motion is detected by Fourier-type mechanisms, preceded by a non-linearity, and slow second-order motion is detected by a process involving a comparison of local luminance features.

EEG spectrum components

in verbal task solving

I.R. Ilyutchenok, institute of Higher Nervous and Neurophysiology, Moscow, Russia

Activity

The purpose of this study was to reveal the EEG correlates of decision-making in the verbal thinking process. During anagram task-solving, the EEG was recorded bilaterally from the frontal, central, temporal, parietal and occipital electrodes (10-20). Two methodological approaches were used: (1) individual ERPs, and (2) single EEG trials, which were then submitted to fast Fourier transformation (FIT) with further averaging for each subject and for the groups. Two groups of results from the anagram task were obtained: (1) successful, with a verbal response, and (2) failure, without any response in a 6-see time period. Several control experiments were done with matching neutral and emotional words and the verbal response. It was shown that different stages of the verbal thinking process are accompanied by certain EEG power patterns. The possibility of distinguishing between success and failure in anagram guessing was based on certain EEG power dynamics revealed in narrow frequency bands (l-2 Hz). The close connection between the verbal thinking process and emotions was shown. Furthermore, positive and negative emotions are differentially represented in terms of EEG functioning with the principal distinction in the theta band.

Magnetic field tomography of cortical processes: precise, real-time mapping of function from non-invasive, non-contact MEG signals Department of Physics, The Open A.A. Ioannides, Milton Keynes MKT 6AA, UK

Uni-

versity,

Distributed source analysis of magnetoencephalograph-

Journal of Psychophysiology 18 (1994) 87-159

115

ic (MEG) signals produces estimates for the (magnetically non-silent part of the primary) current density vector, J. Extracting accurate information about deep generators is still a challenging problem, although distinguishing between superficial and deep activity is feasible, provided that the magnetic field is recorded over a large area. Focal activity from the cortical mantle can be localised with very high accuracy, well within 1 cm. The activity can be mapped millisecond by millisecond, and the analysis of averaged MEG signals from both normal subjects and patients have produced a consistent picture for the location and shape of the generators and the direction of current flow. When maps of J are displayed millisecond by millisecond the functional organisation across wide cortical regions is masked by the relentless buzzing that is ever-present on the cortical mantle. Distributed solutions provide an analogical description that is amenable to further analysis, particularly summation over space and/or time. A straightforward integration of J, is not always useful, because of information lost through cancellation of strong components of opposite polarity. Magnetic field tomography using integrals of lJ12to display both the distribution of activity and the order of activation. Time is discretised into bins, and [J]’ is integrated within each bin. Varying the size of the bin reveals the organisation of task-specific cortical networks on different time scales. If the bin size is small, just a few milliseconds long, monosynaptic transitions are emphasised within neighbouring regions on the same hemisphere or across the midline. Re-entry to primary sensor areas is also evident with small bin size [l]. As the bin size increases the functional organisation across the entire cortical mantle is highlighted. A bin size of 50 msec has been used to study the functional network excited in the CMV GO/NOGO avoidance paradigm [2].

References [l] Ioannides. A.A. (1993) Brain function as revealed by current density analysis of magnetoencephalography signals. Physiol. Meas.. 14: A75-A80. [2] Fenwick, P.B.C., Ioannides, A.A.. Fenton, G.W., Lumsden, .I., Grummich, P., Kober. H.. Daun, A. and Vieth, J. (1993) Estimates of brain activity using magnetic field tomography in a GO/NOGO avoidance paradigm. Brain Topogr., 5: 275-282.

Brain mechanisms thesis in dominant

of the mind: information cortical areas

syn-

A.M. Ivanitsky, Institute of Higher Nervous Activity and Neurophysiology, Moscobc: Russia The main hypothesis of the study is that mental events arise as a result of the information synthesis of qualitatively different information critical for this functional cortical area. This hypothesis was checked in a study of perception