Biomedical subjects
Publications and source records attributed to Kim Dremstrup Nielsen.
This paper summarizes the brain-computer interface (BCI)-related research being conducted at Aalborg University. Namely, an online synchronized BCI system using steady-state visual evoked potentials, and investigations on cortical modulation of movement-related parameters are presented.
A multitude of studies have demonstrated a clear activation of the motor cortex during imagination of various motor tasks; however, it is still unclear if movement-related parameters (movement direction, range of motion, speed, force level and rate of force development) specifically modulate cortical activation as they do during the execution of actual motor tasks. Accordingly, this study examined whether the rate of torque development (RTD) and/or the torque amplitude modulates cortical potentials generated during imaginary motor tasks. Fifteen subjects imagined four different left-sided isometric plantar-flexion tasks, while EEG and EMG recordings were being performed. The averaged EEG activity was analyzed in terms of movement-related potentials (MRPs), consisting of readiness potential (RP), motor potential (MP) and movement-monitoring potential (MMP). It was demonstrated that RTD and torque amplitude indeed modulate cortical activity during imaginary motor tasks. Information concerning movement-related parameters for imaginary plantar-flexion tasks seems to be encoded in the supplementary motor area (SMA) and the primary motor cortex (M1). A comparison between MRPs of imaginary and actual motor tasks revealed that early MRPs were morphologically similar, but differed significantly in amplitude. One of the possible suggestions to explain such a difference may be an "abortion" of ongoing motor programs.
The influence of directional orientation on movement-related potentials (MRPs) during gait initiation and stepping has been investigated in the present study, as well as possible effects caused by the distinction between gait initiation and stepping. Accordingly, electroencephalographic (EEG), electromyographic (EMG) and kinetic recordings were conducted while eight subjects initiated gait and were stepping in three different directions (namely, forward, backward and lateral). Five different movement-related potentials were extracted from the EEG recordings and statistically analyzed. Movement parameters were extracted from kinetic recordings and statistically analyzed as well. Results indicated that variations in directional orientation of gait and stepping were associated to changes in MRPs, but the associations between movement parameters and MRPs were conditional to the kind of task performed. Gait tasks were mainly differentiated in early MRPs while stepping tasks were more differentiated in late MRPs, indicating that differences between gait initiation and stepping might be associated with different levels of preparation and execution. Apparently the changes found in the movement-related potentials were not simply caused by changes in the sensorial input due to perception of the spatial environment, but rather because of variations in the movement kinematics and kinetics.
Based on EEG data recorded from 11 subjects with eyes open and the left mastoid (M) reference, three data sets were generated by re-referencing to the conventional linked mastoids (L), average (A) and the new 'infinity' (I) reference provided by the reference electrode standardization technique (REST, Yao 2001 Physiol. Meas. 22 693-711). The EEG power in the alpha frequency band with the four different references was calculated and compared with respect to the total energy and spatial amplitude weight centre (AWC) coordinates, to compare the effects of different references on power mapping in the frequency domain. Compared with the I reference, the AWCs of the EEG with the M reference show significant shifts to the right, frontal and superficial positions, the L reference significant shifts to frontal and superficial positions, and the A reference shifts the AWC significantly to a deeper position. Furthermore, the power maps of the M and L references have larger total power than the I reference, while that of the A reference has the smallest total power. These results confirm that different choices of reference electrodes result in systematic changes in the distribution of EEG frequency power, and in order to reduce the effect of such systematic shifts on the explanation of EEG mappings, a common reference is necessary for EEG research. We recommend the I reference for objective use in cross-laboratory studies and clinical practices, as it is far from all the other electrodes and can act as a neutral reference.
This study investigates whether rate of torque development (RTD) and/or torque amplitude are reflected in the movement-related potentials (MRPs) preceding and accompanying isometric activation of plantar flexor muscles. Subjects were asked to perform six different tasks involving the left ankle joint. The tasks consisted of voluntary isometric plantar flexions at three different RTDs (two fixed rates and a 'ballistic' task) ending at two different torque amplitudes. The main observations from the analysis of the MRPs were: 1) the readiness potentials (RP) demonstrated a statistically significant discrimination between low and high torque amplitudes; 2) the RP, the motor potentials (MP) and the movement-monitoring potentials (MMP) could be statistically differentiated among the different RTDs; and 3) in general the MRPs demonstrated an ipsilateral tendency in relation to the involved limb. The results indicate that RP is a suitable parameter for differentiation between levels of isometric plantar flexion torque and MP and MMP are sensitive to a differentiation between RTDs. The correlation between MRPs and motor tasks involving different rates of torque development and levels of torque suggests that MRPs may comprise a potential solution for programming of intended movements to be executed by systems based on neural rehabilitation technology.
This study aims to investigate how the blurred scalp alpha power distribution can be segregated on the cortex. EEG recorded from 11 subjects with their eyes closed were utilized to reconstruct the cortically equivalent Charge Layer (CL). Further, the power maps of scalp potential as well CL were generated by Fourier transform. The results showed a distinctly different CL power distribution from that of the scalp potential power, the cortical alpha electric activities were separated significantly into the left and right occipital regions, and in some cases activities at parietal regions were also clearly visibly discriminated. We concluded that the CL model is sensitive, and the blurred scalp activities can be further delineated into separate regions.