Velimir Išgum

Neurophysiological mechanisms underlying motor evoked potentials in anesthetized humans.: Part 1. Recovery time of corticospinal tract direct waves elicited by pairs of transcranial electrical stimuli

Direct (D) corticospinal tract discharges were recorded epidurally in patients at anesthetic depths suppressing indirect (I) activity and were elicited by two equal transcranial electrical stimuli. The recovery of amplitude of the second D wave (D2) was a function of the interstimulus interval (ISI) and the stimulus duration. For example, with a 100 micros pulse, there was no response at an ISI of 1.1 ms, but partial recovery occurred with a 500 micros pulse. This indicates a relative refractory component at this ISI. Both D2 amplitude and conduction time recovered completely using a 4 ms ISI, with evidence of increased amplitude and reduced conduction time (supernormality) at longer ISIs. These findings are relevant in explaining high frequency D and I discharges and facilitation of motor responses by two transcranial magnetic pulses. Furthermore, these data help to understand why an ISI of 4 ms would be optimal in eliciting limb muscle responses when a short train of transcranial stimuli elicits only D waves in anesthetized patients (Deletis et al., Clin Neurophysiol 112 (2001) 445).

Ocular and Cervical Vestibular Evoked Myogenic Potentials in Patients With Multiple Sclerosis

Objectives: The aim of this study was to evaluate latencies and corrected p13-n23 cervical vestibular evoked myogenic potentials (cVEMP) and n10-p13 ocular vestibular evoked myogenic potentials (oVEMP) amplitudes in patients with relapsing remitting multiple sclerosis (MS). Methods: This was a prospective, case-control study. Thirty patients with MS and 15 healthy controls were included. Cervical vestibular evoked myogenic potentials and oVEMP in response to acoustic clicks of 1 ms duration at the intensity of 130 dB SPL and the stimulation frequency of 1 Hz were studied. Signals were divided in segments of 120 ms duration (20 ms before the stimulus and 100 ms after the stimulus) and averaged. Results: In MS group, there was significant latencies prolongation of all sternocleidomastoid responses (p13 and n23) and n10 response of the ocular muscles. The sternocleidomastoid p13-n23 normalized amplitude was significantly higher in MS patients. Prolonged latencies were found in 57% and conduction block in 7% of patients in at least one sternocleidomastoid response in the MS group. Prolonged latencies were found in 30% and conduction block in 40% of patients in at least one ocular response in the MS group. When cVEMP and oVEMP are combined, 80% had pathological finding. When correlating brainstem clinical, brainstem MRI, and cVEMP findings, there was no statistical significance (brainstem clinical vs. cVEMP P = 0.1; brainstem MRI vs. cVEMP P = 0.82). When correlating brainstem clinical, brainstem MRI and oVEMP findings, there was a statistical significant correlation between brainstem clinical versus oVEMP, P = 0.02, whereas there was no statistical significance between brainstem MRI versus oVEMP (P = 0.38). Conclusions: Combination of cVEMP and oVEMP in MS patients allows better estimation of brainstem lesions.

Hilbert-Huang Time-Frequency Analysis of Motor Imagery EEG Data for Brain-Computer Interfaces

Brain-computer interface (BCI) is a technology that provides a non-muscular communication channel between a brain and the outside world. Imagination of left and right hand movements results in spatially distinct brain activation patterns that can be used as control signals for the BCI. Motor imagery (MI) results in the attenuation (event related desynchronization, ERD) or enhancement (event related synchronization, ERS) of amplitude in a certain frequency band of electroencephalogram (EEG). This frequency band can vary between different participants. Therefore time-frequency (TF) analysis is performed in order to extract interesting features from EEG. A simple way of performing TF analysis is by using band power features. In this paper we investigate the perspective of Hilbert-Huang transform (HHT) for extracting TF information used for MI classification. HHT is a method that allows calculation of instantaneous frequency and amplitude of the signal. It does that by decomposing the signal into components for which these parameters can be calculated by means of Hilbert transform. We compare classification accuracy of simple band power features and features obtained by means of HHT on BCI competition IV dataset 2b.

Movement Related Evoked Potentials in Parkinson’s Disease Patients and Healthy Controls

The aim of this study was to demonstrate the role of movement related evoked cortical potentials (MREP) in Parkinson’s disease (PD) diagnostics. The experiment consisted of repeated spontaneous thumb movements in a time interval of 5-10 s. There were two groups of subjects, PD patients and healthy controls. We observed shift in the latency of the beginning of MREP, the Bereitschaftpotential (BP), in patients with PD. The BP started earlier for healthy controls than for the PD patients when the PD patient’s affected hand movement was observed. The BP latency shift was observed for the affected hand, but the beginning of the BP was not influenced for the healthy hand. The later components of MREP were not significantly influenced. The PD patients group was diverse and in accordance with that the standard deviations of MREP components’ amplitudes for this group was much greater that for the controls group.

The electrode setup for vibratory evoked potentials

The difficulties related to the sense of vibration could be characteristics of the specific neurological disorders, so there is a need for measurable and quantifiable information about its functionality. Currently used methods for testing the sense of vibration do not provide appropriate information, and new method of vibratory stimulation was introduced in the area of the neurophysiological research. Method provides repeatable and quantifiable information about the evoked cortical activity, but there was a need for information about the functional integrity of the whole vibratory sensory pathways. The result of this research was the electrode setup that provides information from the Erb’s point through the levels of the cervical spine to the contralateral sensory area at the cortex. Also, the setup consists only of four electrodes for each side of the stimulation (six electrodes all together, because electrodes positioned on the cervical spinal cord are common for both sides of the body), which reduce time necessary for preparation and allows better use for clinical purposes.

Vibratory Evoked Potentials

Numerous pathologies in medicine are characterized with deficit related to deep sense. Diagnostic methods currently used for testing features of deep sense in individuals are extremely subjective and depend on patients’ co-operability, which is not always possible, especially with patients in coma, patients who are not able to communicate or small children.

P9.7 Evoked potentials of spontaneous movements: delayed preparation in Parkinson's disease patients

M. Krbot1, A.B. Sefer1, M. Cifrek2, K. Krbot3, V. Isgum4 1University of Zagreb, Zagreb, Croatia, 2University of Zagreb, Faculty of Electrical Engineering and Computing, Zagreb, Croatia, 3University of Zagreb, School of Medicine, Zagreb, Croatia, 4University Hospital Zagreb, Zagreb, Croatia Introduction: Different kinds of cognitive impairments have specific influence on a working memory. Most of the methods used in a routine cognitive testing of a working memory are behavioral methods and these methods could sometimes be submissive to the influence of patients. Objectives: The aim of our research is to establish reliable and quantitative neurophysiological method appropriate for patients with different kinds of cognitive impairments in order to test features of the working memory. Therefore we performed modified Sternberg memory task. Methods: Twenty-one (14 male and 7 female) healthy right handed adults with no auditory impairments participated in the study. In the Sternberg experiment, sets of two or four digits were acoustically presented to subjects. After the last item in the set, the target digit (probe) was presented. Participants had to indicate whether the probe did (positive probe) or did not (negative probe) belong to the presented set by pressing appropriate buttons. Results of the study are cognitive auditory eventrelated potentials and associated reaction times. Results: Obtained results show that the increase of the memory set size would elicit the increase of the reaction time and the increase of the latency of the specific component of event-related potentials (P300 the cognitive component). The activity in the period in which participants rehearse the previously presented set is stronger expressed for the set consisted of less digits (two). The amplitude of the cognitive component is greater for the positive probe than for the negative probe and the latency of the cognitive component is greater for the negative probe. Conclusions: Findings coming out of this research show that cognitive event-related potentials are an appropriate method for testing features of the working memory. They are in accordance with the presently accepted theory. These findings are being used in order to make a clinical diagnostic method appropriate for patients with different kinds of cognitive impairments.

P9.4 Cognitive event-related potentials: method for testing features of working memory using the Sternberg memory task

M. Krbot1, A.B. Sefer1, M. Cifrek2, K. Krbot3, V. Isgum4 1University of Zagreb, Zagreb, Croatia, 2University of Zagreb, Faculty of Electrical Engineering and Computing, Zagreb, Croatia, 3University of Zagreb, School of Medicine, Zagreb, Croatia, 4University Hospital Zagreb, Zagreb, Croatia Introduction: Different kinds of cognitive impairments have specific influence on a working memory. Most of the methods used in a routine cognitive testing of a working memory are behavioral methods and these methods could sometimes be submissive to the influence of patients. Objectives: The aim of our research is to establish reliable and quantitative neurophysiological method appropriate for patients with different kinds of cognitive impairments in order to test features of the working memory. Therefore we performed modified Sternberg memory task. Methods: Twenty-one (14 male and 7 female) healthy right handed adults with no auditory impairments participated in the study. In the Sternberg experiment, sets of two or four digits were acoustically presented to subjects. After the last item in the set, the target digit (probe) was presented. Participants had to indicate whether the probe did (positive probe) or did not (negative probe) belong to the presented set by pressing appropriate buttons. Results of the study are cognitive auditory eventrelated potentials and associated reaction times. Results: Obtained results show that the increase of the memory set size would elicit the increase of the reaction time and the increase of the latency of the specific component of event-related potentials (P300 the cognitive component). The activity in the period in which participants rehearse the previously presented set is stronger expressed for the set consisted of less digits (two). The amplitude of the cognitive component is greater for the positive probe than for the negative probe and the latency of the cognitive component is greater for the negative probe. Conclusions: Findings coming out of this research show that cognitive event-related potentials are an appropriate method for testing features of the working memory. They are in accordance with the presently accepted theory. These findings are being used in order to make a clinical diagnostic method appropriate for patients with different kinds of cognitive impairments.

P36-14 The comparison of movement related evoked potentials in Parkinson's disease patients and healthy controls

Objective: In an attempt to facilitate the use of biological signals for prediction of accuracy of movement just before the onset of movement, the present study examined the relationships among MRCP parameters as physiological indices and accuracy of task performance. Methods: Experiments were conducted with following protocols; the subject touches on the center of the touch-sensible screen with the forefinger. Next, a target appears 300 pixels away from the touching points in a vertical direction on the screen. The subject moves the forefinger and touches on the center of the displayed target. This trial continued 2 sets of 50 times. MRCP data were acquired with the 128ch EEG system during experiments and the processes of voluntary motion were observed using the high-speed camera. The trigger was generated using the surface EMG on common digital extensor muscle. The data of EEG and the high-speed camera were separated into 2 groups based on the evaluation index of the accuracy. Results: Significant differences between the highand low-performance groups were clearly confirmed on the NS’s slope in MRCPs acquired from frontal region and the most notable change was showed at Fz (p < 0.05). We tried to use support vector machine (SVM) intended to classify NS’s slope into two groups without averaging. After the process of SVM, we compared two groups of NS’s slope to two performance groups that we divided performance data in each trial into newly two groups corresponding NS’s slope classified two groups by SVM. As a result, a relatively high correlation was confirmed between NS’s slope and performance. Conclusions: Based on this findings, we discuss the possibility whether it is possible to predict accuracy just before the movement is executed using MRCPs intended to use as one of the assistive method for BMI.

P4-12 Influence of parameters of the Sternberg memory task (the set size and probe item affiliation) on cognitive event-related potentials

By contrast, in Control, Jaw Movement, and Finger Tapping, they were almost identical among sessions or significantly shorter in Pre than in Post 2 or Post 3. Conclusions: Mastication influences cognitive processing time as reflected by RT and the latency of ERP waveforms. Significance: This is the first study investigating the effect of mastication on the central nervous system using event-related potentials.