Biomedical subjects
K B Böcker
Publications and source records attributed to K B Böcker.
A spatiotemporal dipole model of the stimulus preceding negativity (SPN) prior to feedback stimuli.
Ten subjects performed a time production task, in which they were instructed to press a button four seconds after the presentation of an auditory stimulus. Two seconds after the button press they received either auditory or visual feedback on the temporal accuracy of their response. In such a paradigm negative slow brain potentials can be recorded preceding the response (Movement Preceding Negativity, MPN) as well as preceding the feedback stimulus (Stimulus Preceding Negativity, SPN). Spatiotemporal dipole modelling is used to gain insight in the possible generators of MPN and SPN. From the models it follows that the MPN can be described by one contralateral radial dipole and a bilateral pair of tangential dipoles. All three dipoles are located near central electrode positions, so the generators of the MPN probably reside within the motor cortex. The SPN is modelled by a bilateral frontotemporal pair of dipoles, hypothetically representing activation of the Insulae Reili. The insular cortex is involved in the processing of affective-motivational input, such as carried by the feedback in the present paradigm. However, processing of the information content of the feedback stimulus might by itself also activate the frontal cortex. Both the response and the feedback stimulus are followed by a positive peak, which can be described by the same deep posterior dipole. Both peaks probably represent a P3, which is related to context updating.
The international 10-20 system revisited: cartesian and spherical co-ordinates.
Methods like dipole source localization require an exact specification of the co-ordinates of electrode positions. Different values for the co-ordinates of F3, F4, P3 and P4 are encountered in literature. This is due to the unexpected complexity of the calculations involved and aggravated by an inaccurate but widely used control procedure for the placement of these electrodes. We present a table of co-ordinates for the 10-20 system together with a method for determining the co-ordinates of mid-way positions within the 10-20 system. The consequence of using erroneous co-ordinates on the accuracy of dipole source localization is discussed.
A spatio-temporal dipole model of the readiness potential in humans. I. Finger movement.
Preceding unilateral finger movements readiness potentials (RPs) were recorded in 9 right-handed subjects. The data are presented as time series, potential maps and spatio-temporal dipole models. The latter are interpreted with respect to the underlying generators of the RP. Explicit hypotheses about the unilateral or bilateral activation of particular sensorimotor areas preceding unilateral movements are addressed. The choice for the best spatio-temporal dipole model was guided by a test on the orthogonality of the individual residuals and by a priori neurophysiological evidence. From the final model it is concluded that the initial bilateral symmetrical part of the RP is generated in the posterior walls of the precentral gyrus bilaterally, whereas the later lateralized components originate from the crown of that same gyrus contralaterally. This confirms and extends data from subdural recording, magnetoencephalography (MEG) and EEG.
A spatio-temporal dipole model of the readiness potential in humans. II. Foot movement.
Readiness potentials (RP) have been recorded in 9 subjects who performed voluntary unilateral plantar flexions with the right or left foot. These show a paradoxical ipsilateral dominance. Spatio-temporal dipole models were obtained for these data, by iterative parameter estimation. The non-uniqueness of the inverse problem leads to several models which describe the data almost equally well, and which all pass orthogonality tests for the individual residuals and source waves. In these dipole models the ipsilateral preponderance is attributed to generators in the contralateral hemisphere, which agrees with results from MEG recording. According to these models the main generators of the RP are in the primary motor cortex, one bilaterally in its posterior wall and the other in the contralateral crown. This agrees with earlier results for finger RPs. However, for foot RPs, it was difficult to distinguish individual sub-components in both the observed scalp potentials and the estimated temporal activation patterns of the dipoles. Some of the presented models include a fronto-central dipole which possibly represents activity of the supplementary motor area. It is concluded that this finding is at best suggestive and needs further investigation.
Comments on article by Hufschmidt et al.
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Contingent Negative Variation in migraine.
The Contingent Negative Variation (CNV) is an event-related slow potential. It was recorded in healthy volunteers (n = 8) and in patients suffering from migraine without (n = 12) or with (n = 5) aura, during one (CNV1) and three second (CNV3) foreperiods in a forewarned reaction time task. CNV1 was recorded at the vertex while CNV3 was recorded at multiple electrode sites to assess topographical differences. Seven out of twelve migraine patients without aura had increased CNV1 amplitudes. CNV3 amplitudes were increased as well, but only at electrode positions C3 and C4 and not at Fz. CNV3, which allows for analysis of both an early and a late CNV component, could improve the discrimination of migraine without aura beyond that of CNV1. In migraine with aura all CNV parameters were at control levels, confirming previous results. The data obtained are discussed in terms of arousal, activation and stress and the "biobehavioral model of migraine" (Welch, 1986).
The modulation of somatosensory evoked potentials during the foreperiod of a forewarned reaction time task.
During the foreperiod of a forewarned reaction time (RT) task reflexes in the executing limb increase to a lesser extent than those in the contralateral limb. This is possibly due to input modulation. The present study investigates the possibility of cutaneous sensory modulation during motor preparation by studying the amplitudes of somatosensory evoked potentials (SEPs). Eighteen subjects performed a forewarned RT task with the same fingers as the ones which were electrically stimulated. SEPs evoked during the 4 sec preparatory period were compared to those evoked during movement execution and during the resting period after the motor response respectively. During response execution most SEP components showed smaller amplitudes, i.e., they were gated, which agrees with other studies. In the first part of the foreperiod no SEP modulation was observed. Towards the end of the foreperiod, 500 msec before the response stimulus (RS), the amplitude of the contralateral parietal N70-P100 was significantly decreased, while the P45-N70 showed a similar tendency. However, at the same time the P100-N140 was increased in amplitude. The decrease of the intermediate latency components towards the end of the foreperiod is discussed in terms of gating, while the increase in the long latency component is discussed with respect to a decrease in RT on trials where the fingers were stimulated just before the RS, pointing to the role of attentional mechanisms.