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Temporal alignment of electrocorticographic recordings for upper limb movement.

Talakoub O, Popovic MR, Navaro J, Hamani C, Fonoff ET, Wong W - Front Neurosci (2015)

Bottom Line: In this study, arm speed was used to align neural activity.Four subjects had electrocorticographic (ECoG) electrodes implanted over their primary motor cortex and were asked to perform reaching and retrieving tasks using the upper limb contralateral to the site of electrode implantation.The arm speeds were aligned using a non-linear transformation of the temporal axes resulting in average spectrograms with superior visualization of movement-related neural activity when compared to averaging without alignment.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, University of Toronto Toronto, ON, Canada ; Institute of Biomaterials and Biomedical Engineering, University of Toronto Toronto, ON, Canada.

ABSTRACT
The detection of movement-related components of the brain activity is useful in the design of brain-machine interfaces. A common approach is to classify the brain activity into a number of templates or states. To find these templates, the neural responses are averaged over each movement task. For averaging to be effective, one must assume that the neural components occur at identical times over repeated trials. However, complex arm movements such as reaching and grasping are prone to cross-trial variability due to the way movements are performed. Typically initiation time, duration of movement and movement speed are variable even as a subject tries to reproduce the same task identically across trials. Therefore, movement-related neural activity will tend to occur at different times across the trials. Due to this mismatch, the averaging of neural activity will not bring into salience movement-related components. To address this problem, we present a method of alignment that accounts for the variabilities in the way the movements are conducted. In this study, arm speed was used to align neural activity. Four subjects had electrocorticographic (ECoG) electrodes implanted over their primary motor cortex and were asked to perform reaching and retrieving tasks using the upper limb contralateral to the site of electrode implantation. The arm speeds were aligned using a non-linear transformation of the temporal axes resulting in average spectrograms with superior visualization of movement-related neural activity when compared to averaging without alignment.

No MeSH data available.


Related in: MedlinePlus

Comparing the warping of spectrograms (left panels) with the spectrograms of signals warped in the time-domain (right panels). Percentile changes in spectral density of the ECoG activity is shown with respect to the rest period. (A/B,C/D,E/F,G/H) shows results for Subject #1, #2, #3, #4 respectively. The distortion is evident in the spectrograms after warping is carried out on the time-domain signal.
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Figure 6: Comparing the warping of spectrograms (left panels) with the spectrograms of signals warped in the time-domain (right panels). Percentile changes in spectral density of the ECoG activity is shown with respect to the rest period. (A/B,C/D,E/F,G/H) shows results for Subject #1, #2, #3, #4 respectively. The distortion is evident in the spectrograms after warping is carried out on the time-domain signal.

Mentions: The results of this study were obtained through the alignment of the spectrograms for cortical activities. An alternative approach is to carry out the alignment directly on the time-domain signal itself. This is not advisable because warping the signal directly distorts its frequency content. Nevertheless, we show an example of what would happen if such an operation were carried out. Warping was applied directly to the ECoG signal followed by a calculation of its spectrogram. Figure 6 compares the averaged spectrogram obtained by this new method with the spectrograms obtained from the original (and preferred) method. We note that the results from warping the time-domain signals are less clear and show obvious distortions due to the prolongation of harmonic signals from line noise as seen in Figures 6B,D,F,H.


Temporal alignment of electrocorticographic recordings for upper limb movement.

Talakoub O, Popovic MR, Navaro J, Hamani C, Fonoff ET, Wong W - Front Neurosci (2015)

Comparing the warping of spectrograms (left panels) with the spectrograms of signals warped in the time-domain (right panels). Percentile changes in spectral density of the ECoG activity is shown with respect to the rest period. (A/B,C/D,E/F,G/H) shows results for Subject #1, #2, #3, #4 respectively. The distortion is evident in the spectrograms after warping is carried out on the time-domain signal.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4292555&req=5

Figure 6: Comparing the warping of spectrograms (left panels) with the spectrograms of signals warped in the time-domain (right panels). Percentile changes in spectral density of the ECoG activity is shown with respect to the rest period. (A/B,C/D,E/F,G/H) shows results for Subject #1, #2, #3, #4 respectively. The distortion is evident in the spectrograms after warping is carried out on the time-domain signal.
Mentions: The results of this study were obtained through the alignment of the spectrograms for cortical activities. An alternative approach is to carry out the alignment directly on the time-domain signal itself. This is not advisable because warping the signal directly distorts its frequency content. Nevertheless, we show an example of what would happen if such an operation were carried out. Warping was applied directly to the ECoG signal followed by a calculation of its spectrogram. Figure 6 compares the averaged spectrogram obtained by this new method with the spectrograms obtained from the original (and preferred) method. We note that the results from warping the time-domain signals are less clear and show obvious distortions due to the prolongation of harmonic signals from line noise as seen in Figures 6B,D,F,H.

Bottom Line: In this study, arm speed was used to align neural activity.Four subjects had electrocorticographic (ECoG) electrodes implanted over their primary motor cortex and were asked to perform reaching and retrieving tasks using the upper limb contralateral to the site of electrode implantation.The arm speeds were aligned using a non-linear transformation of the temporal axes resulting in average spectrograms with superior visualization of movement-related neural activity when compared to averaging without alignment.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, University of Toronto Toronto, ON, Canada ; Institute of Biomaterials and Biomedical Engineering, University of Toronto Toronto, ON, Canada.

ABSTRACT
The detection of movement-related components of the brain activity is useful in the design of brain-machine interfaces. A common approach is to classify the brain activity into a number of templates or states. To find these templates, the neural responses are averaged over each movement task. For averaging to be effective, one must assume that the neural components occur at identical times over repeated trials. However, complex arm movements such as reaching and grasping are prone to cross-trial variability due to the way movements are performed. Typically initiation time, duration of movement and movement speed are variable even as a subject tries to reproduce the same task identically across trials. Therefore, movement-related neural activity will tend to occur at different times across the trials. Due to this mismatch, the averaging of neural activity will not bring into salience movement-related components. To address this problem, we present a method of alignment that accounts for the variabilities in the way the movements are conducted. In this study, arm speed was used to align neural activity. Four subjects had electrocorticographic (ECoG) electrodes implanted over their primary motor cortex and were asked to perform reaching and retrieving tasks using the upper limb contralateral to the site of electrode implantation. The arm speeds were aligned using a non-linear transformation of the temporal axes resulting in average spectrograms with superior visualization of movement-related neural activity when compared to averaging without alignment.

No MeSH data available.


Related in: MedlinePlus