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Potential for unreliable interpretation of EEG recorded with microelectrodes
Author(s) -
Stacey William C.,
Kellis Spencer,
Greger Bradley,
Butson Christopher R.,
Patel Paras R.,
Assaf Trevor,
Mihaylova Temenuzhka,
Glynn Simon
Publication year - 2013
Publication title -
epilepsia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.687
H-Index - 191
eISSN - 1528-1167
pISSN - 0013-9580
DOI - 10.1111/epi.12202
Subject(s) - microelectrode , electroencephalography , multielectrode array , amplifier , signal (programming language) , electrode , electrophysiology , electrical impedance , artifact (error) , biomedical engineering , computer science , pattern recognition (psychology) , neuroscience , artificial intelligence , chemistry , psychology , medicine , electrical engineering , telecommunications , engineering , bandwidth (computing) , programming language
Summary Purpose Recent studies in epilepsy, cognition, and brain machine interfaces have shown the utility of recording intracranial electroencephalography (i EEG ) with greater spatial resolution. Many of these studies utilize microelectrodes connected to specialized amplifiers that are optimized for such recordings. We recently measured the impedances of several commercial microelectrodes and demonstrated that they will distort i EEG signals if connected to clinical EEG amplifiers commonly used in most centers. In this study we demonstrate the clinical implications of this effect and identify some of the potential difficulties in using microelectrodes. Methods Human i EEG data were digitally filtered to simulate the signal recorded by a hybrid grid (two macroelectrodes and eight microelectrodes) connected to a standard EEG amplifier. The filtered iEEG data were read by three trained epileptologists, and high frequency oscillations ( HFO s) were detected with a well‐known algorithm. The filtering method was verified experimentally by recording an injected EEG signal in a saline bath with the same physical acquisition system used to generate the model. Several electrodes underwent scanning electron microscopy ( SEM ). Key Findings Macroelectrode recordings were unaltered compared to the source i EEG signal, but microelectrodes attenuated low frequencies. The attenuated signals were difficult to interpret: all three clinicians changed their clinical scoring of slowing and seizures when presented with the same data recorded on different sized electrodes. The HFO detection algorithm was oversensitive with microelectrodes, classifying many more HFO s than when the same data were recorded with macroelectrodes. In addition, during experimental recordings the microelectrodes produced much greater noise as well as large baseline fluctuations, creating sharply contoured transients, and superimposed “false” HFO s. SEM of these microelectrodes demonstrated marked variability in exposed electrode surface area, lead fractures, and sharp edges. Significance Microelectrodes should not be used with low impedance (<1 GΩ) amplifiers due to severe signal attenuation and variability that changes clinical interpretations. The current method of preparing microelectrodes can leave sharp edges and nonuniform amounts of exposed wire. Even when recorded with higher impedance amplifiers, microelectrode data are highly prone to artifacts that are difficult to interpret. Great care must be taken when analyzing i EEG from high impedance microelectrodes.