Frequency dependence of the transmission of the EEG from cortex to scalp

Pfurtscheller, Gert; Cooper, R.

doi:10.1016/0013-4694(75)90215-1

Cited by 210 publications

(78 citation statements)

References 6 publications

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“…However, scalp EEG studies have typically focused on gamma activity in lower frequencies (< 50 Hz). Signal changes in higher gamma frequencies are difficult, if not impossible, to observe in scalp EEG recordings (Pfurtscheller and Cooper, 1975). Although such frequencies are accessible in microelectrode recordings of local field potentials in animals, the small change in signal energy observed at high-gamma frequencies in ECoG are likely to occur at the network level and might be overlooked at such a fine resolution.…”

Section: Discussionmentioning

confidence: 99%

“…However, high frequency cortical activity is significantly attenuated by intervening cranial tissues in scalp recordings (Cooper et al, 1965;Pfurtscheller and Cooper, 1975). Indeed, the extended frequency response of invasive EEG recordings has shown that during functional activation of cerebral cortex, gamma activity occurs over a much broader range of frequencies that extend far beyond the traditional 40-Hz gamma band typically observed in scalp EEG (Crone et al, 1998a;Crone et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

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High-frequency gamma activity (80–150Hz) is increased in human cortex during selective attention

Ray

Niebur

Hsiao

et al. 2008

Clinical Neurophysiology

216

163

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Objective: To study the role of gamma oscillations (>30 Hz) in selective attention using subdural electrocorticography (ECoG) in humans. Methods:We recorded ECoG in human subjects implanted with subdural electrodes for epilepsy surgery. Sequences of auditory tones and tactile vibrations of 800 ms duration were presented asynchronously, and subjects were asked to selectively attend to one of the two stimulus modalities in order to detect an amplitude increase at 400 ms in some of the stimuli.Results: Event-related ECoG gamma activity was greater over auditory cortex when subjects attended auditory stimuli and was greater over somatosensory cortex when subjects attended vibrotactile stimuli. Furthermore, gamma activity was also observed over prefrontal cortex when stimuli appeared in either modality, but only when they were attended. Attentional modulation of gamma power began ∼400 ms after stimulus onset, consistent with the temporal demands on attention. The increase in gamma activity was greatest at frequencies between 80 and 150 Hz, in the so-called high gamma frequency range.Conclusions: There appears to be a strong link between activity in the high-gamma range (80-150 Hz) and selective attention.Significance: Selective attention is correlated with increased activity in a frequency range that is significantly higher than what has been reported previously using EEG recordings.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

High-frequency gamma activity (80–150Hz) is increased in human cortex during selective attention

Ray

Niebur

Hsiao

et al. 2008

Clinical Neurophysiology

216

163

View full text Add to dashboard Cite

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“…In most reports, LEP are recorded from the scalp, where they are limited by muscle and blink artifacts, by low-pass and spatial filtering at the scalp, skull, and CSF (Cooper et al 1965;Gevins et al 1994;Lenz et al 1998Lenz et al , 2000Ohara et al 2004aOhara et al , 2004bOhara et al , 2004cPfurtscheller and Cooper, 1975;Valeriani et al 2000;Vogel et al 2003;Wang et al 2007), and by large interelectrode distances (Garcia-Larrea et al 2003). We have applied subdural recordings, a technique that brings increased resolution and clarity to the study of human S1 cortical pain mechanisms (Ohara et al 2004b;Scherg 1992).…”

Section: Discussionmentioning

confidence: 99%

Dipole source analyses of laser evoked potentials obtained from subdural grid recordings from primary somatic sensory cortex

Baumgärtner

Vogel

Ohara

et al. 2011

Journal of Neurophysiology

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The cortical potentials evoked by cutaneous application of a laser stimulus (laser evoked potentials, LEP) often include potentials in the primary somatic sensory cortex (S1), which may be located within the subdivisions of S1 including Brodmann areas 3A, 3B, 1, and 2. The precise location of the LEP generator may clarify the pattern of activation of human S1 by painful stimuli. We now test the hypothesis that the generators of the LEP are located in human Brodmann area 1 or 3A within S1. Local field potential (LFP) source analysis of the LEP was obtained from subdural grids over sensorimotor cortex in two patients undergoing epilepsy surgery. The relationship of LEP dipoles was compared with dipoles for somatic sensory potentials evoked by median nerve stimulation (SEP) and recorded in area 3B (see Baumgärtner U, Vogel H, Ohara S, Treede RD, Lenz FA. J Neurophysiol 104: 3029–3041, 2010). Both patients had an early radial dipole in S1. The LEP dipole was located medial, anterior, and deep to the SEP dipole, which suggests a nociceptive dipole in area 3A. One patient had a later tangential dipole with positivity posterior, which is opposite to the orientation of the SEP dipole in area 3B. The reversal of orientations between modalities is consistent with the cortical surface negative orientation resulting from superficial termination of thalamocortical neurons that receive inputs from the spinothalamic tract. Therefore, the present results suggest that the LEP may result in a radial dipole consistent with a generator in area 3A and a putative later tangential generator in area 3B.

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“…that may influence the sampling problem. Furthermore, our simulations were based on the assumption that cortical amplitude at least remains constant (but likely decreases) with increasing spatial frequency (Nunez, 1981;Pfurtscheller & Cooper, 1975; van Rotterdam, Lopes da Silva, van den Ende, Viergever, & Hermans, 1982). Furthermore, the key factor for simulation and source localization studies is the conductivity of the skull, which, although widely assumed to be 80 times the conductivity of the brain, is in fact unknown (Law, 1993).…”

Section: Spatial Low-pass Filtering By the Headmentioning

confidence: 99%

Estimating the spatial Nyquist of the human EEG

Srinivasan

Tucker

Murias

1998

Behavior Research Methods, Instruments, & Computers

227

149

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The discrete sampling of the brain's electrical field at the scalp surface with individual recording sensors is subject to the same sampling error as the discrete sampling of the time series at anyone sensor with analog-to-digital conversion. Unlike temporal sampling, spatial sampling is intrinsically discrete, so that the post hoc application of analog anti-aliasing filters is not possible. However, the skull acts as a low-pass spatial filter ofthe brain's electrical field, attenuating the high spatial frequency information. Because of the skull's spatial filtering, a discrete sampling of the spatial field with a reasonable number of scalp electrodes is possible. In this paper, we provide theoretical and experimental evidence that adequately sampling the human electroencephalograph (EEG) across the full surface of the head requires a minimum of 128 sensors. Further studies with each of the major EEG and event-related potential phenomena are required in order to determine the spatial frequency of these phenomena and in order to determine whether additional increases in sensor density beyond 128 channels will improve the spatial resolution of the scalp EEG.When the time series ofan electroencephalogram (EEG) channel is sampled discretely, the Nyquist theorem specifies that the highest measurable frequency is half the sampling rate. For example, with a 250 sample/sec analog-to-digital conversion rate, the highest frequency that can be resolved is 125 Hz. In actuality, because of phase alignment, it is necessary to discretely sample (digitize) the signal at a rate at least 2.5 times the highest frequency component ofthe signal (Bendat & Piersol, 1986). Signal frequencies higher than the Nyquist frequency are not only poorly characterized; they alias or appear misleadingly as increased energy at lower frequencies. To avoid aliasing, it is necessary to eliminate the frequency components of the signal that are higher than the Nyquist frequency through analog filtering.The electrical field of the brain generates a potential distribution that is continuous over the surface of the head. The discretization ofthis spatial EEG or averaged eventrelated potential (ERP) signal with scalp electrodes is also subject to the Nyquist theorem. Ifthe spatial sampling is Correspondence concerning this article should be addressed to D. M.Tucker, Electrical Geodesics, Inc., Riverfront Research Park, 1811 Garden Avenue, Suite 104, Eugene, OR 97403 (e-mail: dtucker@egi.com).Note: ElectricalGeodesics, Inc. sells 64-, 128-,and 256-channelEEG systems and thus has a commercial interest in promoting dense sensor array technology.-Editor

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Frequency dependence of the transmission of the EEG from cortex to scalp

Cited by 210 publications

References 6 publications

High-frequency gamma activity (80–150Hz) is increased in human cortex during selective attention

High-frequency gamma activity (80–150Hz) is increased in human cortex during selective attention

Dipole source analyses of laser evoked potentials obtained from subdural grid recordings from primary somatic sensory cortex

Estimating the spatial Nyquist of the human EEG

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