Journal article
Manifestation of ocular-muscle EMG contamination in human intracranial recordings
NeuroImage (Orlando, Fla.), Vol.54(1), pp.213-233
01/01/2011
DOI: 10.1016/j.neuroimage.2010.08.002
PMCID: PMC2975438
PMID: 20696256
Abstract
It is widely assumed that intracranial recordings from the brain are only minimally affected by contamination due to ocular-muscle electromyogram (oEMG). Here we show that this is not always the case. In intracranial recordings from five surgical epilepsy patients we observed that eye movements caused a transient biphasic potential at the onset of a saccade, resembling the saccadic spike potential commonly seen in scalp EEG, accompanied by an increase in broadband power between 20 and 200Hz. Using concurrently recorded eye movements and high-density intracranial EEG (iEEG) we developed a detailed overview of the spatial distribution and temporal characteristics of the saccade-related oculomotor signal within recordings from ventral, medial and lateral temporal cortex. The occurrence of the saccadic spike was not explained solely by reference contact location, and was observed near the temporal pole for small (<2deg) amplitude saccades and over a broad area for larger saccades. We further examined the influence of saccade-related oEMG contamination on measurements of spectral power and interchannel coherence. Contamination manifested in both spectral power and coherence measurements, in particular, over the anterior half of the ventral and medial temporal lobe. Next, we compared methods for removing the contaminating signal and found that nearest-neighbor bipolar re-referencing and ICA filtering were effective for suppressing oEMG at locations far from the orbits, but tended to leave some residual contamination at the temporal pole. Finally, we show that genuine cortical broadband gamma responses observed in averaged data from ventral temporal cortex can bear a striking similarity in time course and band-width to oEMG contamination recorded at more anterior locations. We conclude that eye movement-related contamination should be ruled out when reporting high gamma responses in human intracranial recordings, especially those obtained near anterior and medial temporal lobe.
►EMG from ocular muscles (oEMG) may contaminate intracranial recordings. ►oEMG contamination may closely resemble visual gamma band responses. ►The distribution of oEMG depends critically on referencing scheme. ►ICA filtering and local rereferencing can both suppress oEMG.
Details
- Title: Subtitle
- Manifestation of ocular-muscle EMG contamination in human intracranial recordings
- Creators
- Christopher K Kovach - Department of Neurosurgery, The University of Iowa College of Medicine, Iowa City, IA, USANaotsugu Tsuchiya - Division of Humanities and Social Sciences, California Institute of Technology, Pasadena, CA, USAHiroto Kawasaki - Department of Neurosurgery, The University of Iowa College of Medicine, Iowa City, IA, USAHiroyuki Oya - Department of Neurosurgery, The University of Iowa College of Medicine, Iowa City, IA, USAMathew A Howard - Department of Neurosurgery, The University of Iowa College of Medicine, Iowa City, IA, USARalph Adolphs - Department of Neurosurgery, The University of Iowa College of Medicine, Iowa City, IA, USA
- Resource Type
- Journal article
- Publication Details
- NeuroImage (Orlando, Fla.), Vol.54(1), pp.213-233
- DOI
- 10.1016/j.neuroimage.2010.08.002
- PMID
- 20696256
- PMCID
- PMC2975438
- NLM abbreviation
- Neuroimage
- ISSN
- 1053-8119
- eISSN
- 1095-9572
- Publisher
- Elsevier Inc
- Grant note
- name: NIH, award: R03 MH070497-01A2; name: NIH, award: R01 D
- Language
- English
- Date published
- 01/01/2011
- Academic Unit
- Neurology; Iowa Neuroscience Institute; Neurosurgery; Otolaryngology
- Record Identifier
- 9984020796602771
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