Suspicious looking mu rhythm on <scp>SEEG</scp>

A 39-year-old gentleman was investigated with stereo-electroencephalography (SEEG) in the context of multiple cavernomas (left posterior frontal and parietal) and recurrent seizures despite a previous left amygdalectomy. Abundant high-amplitude activity in long runs was suspected to be epileptiform due to its morphology and close association with the left parietal cavernoma. With right hand movement and sleep, the discharges consistently attenuated, in contrast to other epileptiform discharges, leading us to conclude that it was mu rhythm (Figures 1 and 2). Mu rhythm, a well-recognized variant of the dominant alpha/beta rhythms seen in the central sensori-motor regions,1 is blocked by contralateral voluntary/passive movement or somatosensory stimulation.2 Its generating sources are located at the somatosensory cortex.3-5 To the best of our knowledge, there is only one other study that assessed mu in three patients with SEEG.6 Literature on the appearance of normal variants in SEEG is lacking. Care should be taken that physiological rhythms are not mistaken for epileptiform activity. When in doubt, reactivity and activity protocols can be helpful. No funding information. AJS has no relevant disclosures. ASM has no relevant disclosures. GP has no relevant disclosures. Telephonic consent for publication was obtained from the patient. The data that support the findings of this study are available from the corresponding author upon reasonable request. Data S1. Data S2. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. How can normal variant mu rhythm present on SEEG? Where is mu rhythm most commonly seen? What attenuates mu rhythm, both on scalp and stereo-EEG? Answers may be found in the Supporting information.