What are less common focal patterns on EEG?

Updated: Aug 06, 2019
  • Author: Selim R Benbadis, MD; Chief Editor: Helmi L Lutsep, MD  more...
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An abnormal response to photic stimulation can be seen in focal lesions. Normal photic driving has long been known to be potentially reduced on the side of a lesion. Posterior destructive lesions are particularly likely to attenuate the driving response, but some reports have described an enhanced photic response on the side of dysfunction. However, since the normal driving response can be quite asymmetric, such a finding should be accompanied by a more reliable abnormality such as slowing of the waveform frequency in order to be interpreted as abnormal.

The Bancaud phenomenon refers to the unilateral loss of reactivity of a normal rhythm and initially was described in the context of the alpha rhythm. It should be considered a pathological finding only when associated with other more definite abnormalities, such as slowing.

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