TY  - JOUR
AU  - Stokić, Miodrag
AU  - Milovanović, Dragan
AU  - Ljubisavljević, Milos R.
AU  - Nenadović, Vanja
AU  - Cukić, Milena
PY  - 2015
UR  - http://intor.torlakinstitut.com/handle/123456789/428
AB  - The objective of this preliminary study was to quantify changes in complexity of EEG using fractal dimension (FD) alongside linear methods of spectral power, event-related spectral perturbations, coherence, and source localization of EEG generators for theta (4-7 Hz), alpha (8-12 Hz), and beta (13-23 Hz) frequency bands due to a memory load effect in an auditory-verbal short-term memory (AVSTM) task for words. We examined 20 healthy individuals using the Sternberg's paradigm with increasing memory load (three, five, and seven words). The stimuli were four-letter words. Artifact-free 5-s EEG segments during retention period were analyzed. The most significant finding was the increase in FD with the increase in memory load in temporal regions T3 and T4, and in parietal region Pz, while decrease in FD with increase in memory load was registered in frontal midline region Fz. Results point to increase in frontal midline (Fz) theta spectral power, decrease in alpha spectral power in parietal region-Pz, and increase in beta spectral power in T3 and T4 region with increase in memory load. Decrease in theta coherence within right hemisphere due to memory load was obtained. Alpha coherence increased in posterior regions with anterior decrease. Beta coherence increased in fronto-temporal regions. Source localization delineated theta activity increase in frontal midline region, alpha decrease in superior parietal region, and beta increase in superior temporal gyrus with increase in memory load. In conclusion, FD as a nonlinear measure may serve as a sensitive index for quantifying dynamical changes in EEG signals during AVSTM tasks.
PB  - Springer, New York
T2  - Experimental Brain Research
T1  - Memory load effect in auditory-verbal short-term memory task: EEG fractal and spectral analysis
EP  - 3038
IS  - 10
SP  - 3023
VL  - 233
DO  - 10.1007/s00221-015-4372-z
ER  - 

@article{
author = "Stokić, Miodrag and Milovanović, Dragan and Ljubisavljević, Milos R. and Nenadović, Vanja and Cukić, Milena",
year = "2015",
abstract = "The objective of this preliminary study was to quantify changes in complexity of EEG using fractal dimension (FD) alongside linear methods of spectral power, event-related spectral perturbations, coherence, and source localization of EEG generators for theta (4-7 Hz), alpha (8-12 Hz), and beta (13-23 Hz) frequency bands due to a memory load effect in an auditory-verbal short-term memory (AVSTM) task for words. We examined 20 healthy individuals using the Sternberg's paradigm with increasing memory load (three, five, and seven words). The stimuli were four-letter words. Artifact-free 5-s EEG segments during retention period were analyzed. The most significant finding was the increase in FD with the increase in memory load in temporal regions T3 and T4, and in parietal region Pz, while decrease in FD with increase in memory load was registered in frontal midline region Fz. Results point to increase in frontal midline (Fz) theta spectral power, decrease in alpha spectral power in parietal region-Pz, and increase in beta spectral power in T3 and T4 region with increase in memory load. Decrease in theta coherence within right hemisphere due to memory load was obtained. Alpha coherence increased in posterior regions with anterior decrease. Beta coherence increased in fronto-temporal regions. Source localization delineated theta activity increase in frontal midline region, alpha decrease in superior parietal region, and beta increase in superior temporal gyrus with increase in memory load. In conclusion, FD as a nonlinear measure may serve as a sensitive index for quantifying dynamical changes in EEG signals during AVSTM tasks.",
publisher = "Springer, New York",
journal = "Experimental Brain Research",
title = "Memory load effect in auditory-verbal short-term memory task: EEG fractal and spectral analysis",
pages = "3038-3023",
number = "10",
volume = "233",
doi = "10.1007/s00221-015-4372-z"
}

Stokić, M., Milovanović, D., Ljubisavljević, M. R., Nenadović, V.,& Cukić, M.. (2015). Memory load effect in auditory-verbal short-term memory task: EEG fractal and spectral analysis. in Experimental Brain Research
Springer, New York., 233(10), 3023-3038.
https://doi.org/10.1007/s00221-015-4372-z

Stokić M, Milovanović D, Ljubisavljević MR, Nenadović V, Cukić M. Memory load effect in auditory-verbal short-term memory task: EEG fractal and spectral analysis. in Experimental Brain Research. 2015;233(10):3023-3038.
doi:10.1007/s00221-015-4372-z .

Stokić, Miodrag, Milovanović, Dragan, Ljubisavljević, Milos R., Nenadović, Vanja, Cukić, Milena, "Memory load effect in auditory-verbal short-term memory task: EEG fractal and spectral analysis" in Experimental Brain Research, 233, no. 10 (2015):3023-3038,
https://doi.org/10.1007/s00221-015-4372-z . .

TY  - JOUR
AU  - Cukić, Milena
AU  - Oommen, J.
AU  - Mutavdžić, D.
AU  - Jorgovanović, N.
AU  - Ljubisavljević, M.
PY  - 2013
UR  - http://intor.torlakinstitut.com/handle/123456789/392
AB  - The aim of this study was to examine whether single-pulse transcranial magnetic stimulation (spTMS) affects the pattern of corticospinal activity once voluntary drive has been restored after spTMS-induced EMG silence. We used fractal dimension (FD) to explore the 'complexity' of the electromyography (EMG) signal, and median frequency of the spectra (MDF) to examine changes in EMG spectral characteristics. FD and MDF of the raw EMG epochs immediately before were compared with those obtained from epochs after the EMG silence. Changes in FD and MDF after spTMS were examined with three levels of muscle contraction corresponding to weak (20-40 %), moderate (40-60 %) and strong (60-80 % of maximal voluntary contraction) and three intensities of stimulation set at 10, 20 and 30 % above the resting motor threshold. FD was calculated using the Higuchi fractal dimension algorithm. Finally, to discern the origin of FD changes between the CNS and muscle, we compared the effects of spTMS with the effects of peripheral nerve stimulation (PNS) on FD and MDF. The results show that spTMS induced significant decrease in both FD and MDF of EMG signal after stimulation. PNS did not have any significant effects on FD nor MDF. Changes in TMS intensity did not have any significant effect on FD or MDF after stimulation nor had the strength of muscle contraction. However, increase in contraction strength decreased FD before stimulation but only between weak and moderate contraction. The results suggest that the effects of spTMS on corticospinal activity, underlying voluntary motor output, outlast the TMS stimulus. It appears that the complexity of the EMG signal is reduced after spTMS, suggesting that TMS alters the dynamics of the ongoing corticospinal activity most likely temporarily synchronizing the neural network activity. Further studies are needed to confirm whether observed changes after TMS occur at the cortical level.
PB  - Springer, New York
T2  - Experimental Brain Research
T1  - The effect of single-pulse transcranial magnetic stimulation and peripheral nerve stimulation on complexity of EMG signal: fractal analysis
EP  - 104
IS  - 1
SP  - 97
VL  - 228
DO  - 10.1007/s00221-013-3541-1
ER  - 

@article{
author = "Cukić, Milena and Oommen, J. and Mutavdžić, D. and Jorgovanović, N. and Ljubisavljević, M.",
year = "2013",
abstract = "The aim of this study was to examine whether single-pulse transcranial magnetic stimulation (spTMS) affects the pattern of corticospinal activity once voluntary drive has been restored after spTMS-induced EMG silence. We used fractal dimension (FD) to explore the 'complexity' of the electromyography (EMG) signal, and median frequency of the spectra (MDF) to examine changes in EMG spectral characteristics. FD and MDF of the raw EMG epochs immediately before were compared with those obtained from epochs after the EMG silence. Changes in FD and MDF after spTMS were examined with three levels of muscle contraction corresponding to weak (20-40 %), moderate (40-60 %) and strong (60-80 % of maximal voluntary contraction) and three intensities of stimulation set at 10, 20 and 30 % above the resting motor threshold. FD was calculated using the Higuchi fractal dimension algorithm. Finally, to discern the origin of FD changes between the CNS and muscle, we compared the effects of spTMS with the effects of peripheral nerve stimulation (PNS) on FD and MDF. The results show that spTMS induced significant decrease in both FD and MDF of EMG signal after stimulation. PNS did not have any significant effects on FD nor MDF. Changes in TMS intensity did not have any significant effect on FD or MDF after stimulation nor had the strength of muscle contraction. However, increase in contraction strength decreased FD before stimulation but only between weak and moderate contraction. The results suggest that the effects of spTMS on corticospinal activity, underlying voluntary motor output, outlast the TMS stimulus. It appears that the complexity of the EMG signal is reduced after spTMS, suggesting that TMS alters the dynamics of the ongoing corticospinal activity most likely temporarily synchronizing the neural network activity. Further studies are needed to confirm whether observed changes after TMS occur at the cortical level.",
publisher = "Springer, New York",
journal = "Experimental Brain Research",
title = "The effect of single-pulse transcranial magnetic stimulation and peripheral nerve stimulation on complexity of EMG signal: fractal analysis",
pages = "104-97",
number = "1",
volume = "228",
doi = "10.1007/s00221-013-3541-1"
}

Cukić, M., Oommen, J., Mutavdžić, D., Jorgovanović, N.,& Ljubisavljević, M.. (2013). The effect of single-pulse transcranial magnetic stimulation and peripheral nerve stimulation on complexity of EMG signal: fractal analysis. in Experimental Brain Research
Springer, New York., 228(1), 97-104.
https://doi.org/10.1007/s00221-013-3541-1

Cukić M, Oommen J, Mutavdžić D, Jorgovanović N, Ljubisavljević M. The effect of single-pulse transcranial magnetic stimulation and peripheral nerve stimulation on complexity of EMG signal: fractal analysis. in Experimental Brain Research. 2013;228(1):97-104.
doi:10.1007/s00221-013-3541-1 .

Cukić, Milena, Oommen, J., Mutavdžić, D., Jorgovanović, N., Ljubisavljević, M., "The effect of single-pulse transcranial magnetic stimulation and peripheral nerve stimulation on complexity of EMG signal: fractal analysis" in Experimental Brain Research, 228, no. 1 (2013):97-104,
https://doi.org/10.1007/s00221-013-3541-1 . .