Breach rhythm: The EEG related to skull defects

Magnetoencephalography signals are influenced by skull defects

“…This is consistent with the finding of Okada et al (1999a), who found an increase in amplitude by a factor of 4-10 between the EEG signal of a somatic evoked potential at the cortical surface compared with that at the skull surface of a juvenile swine. The potential map amplitude increase also matches clinical findings in humans, which are reported as factors of up to 3 (Cobb et al, 1979;Radhakrishnan et al, 1999) and of up to 5 (average, 1.5) in 30 patients (Kendel, 1970).…”

“…The skull has the most resistive tissue of the head, and therefore has the strongest influence on these techniques. The neurological term breach rhythm describes an increase in the amplitude of alpha, beta, and mu rhythms of the brain that occurs proximal to or over post-surgical skull defects (Cobb et al, 1979). At these locations, the absence of skull tissue allows volume currents to reach the electrodes largely unfiltered and unattenuated.…”

Delta–alpha ratio correlates with level of recovery after neurorehabilitation in patients with acquired brain injury

“…Other phenomenon which may influence the lack of results of this index is the presence of breach rhythms in certain EEGs: in cases of skull defects or craniotomy, we can find a surplus of fast activity amplitude and/or sharply focal mu-like rhythms in locations near the skull defect (Cobb et al, 1979). The impact of this phenomenon would be diluted in DAR and PRI, because both are calculated by means of grand averages of all scalp power within the different frequency bands.…”

Signal quality of simultaneously recorded invasive and non-invasive EEG

“…Such volume conduction would constitute a reverse breach effect as was proposed by of J. Gotman, cited in Otsubo et al (2008), as a mechanism for intracranially measurable EMG artifacts. The classical breach effect consists of focally increased amplitudes of alpha and beta activities in the scalp recorded EEG over or near bone defects (Cobb et al, 1979). Reverse breach effects can, therefore, also be expected to show up as rather focal changes in ECoG recordings.…”