Test Device (SOFT ECoG subdural grid electrode): used for recording. During epilepsy surgery, in addition to standard clinical protocol (recording with comparator device), subjects will undergo ≥ 2 additional intracranial recordings with the SOFT ECoG flexible high density electrode grid (TD). Recording will be registered pre- and post-resection.

All procedures will be conducted according to standard clinical practice. Any medical decision making will be done using the standard of care CE-marked device (CD). The investigational, non-CE marked device is not used for clinical decision making.

Performance in terms of signal quality is assessed via background signal to noise ratio (SNR). Only channels which record properly based on visual inspection (no noise, no flat line) will be included in the background SNR calculation. For the pre-resection recordings (SITUATION I/I*), the background SNR per (included) channel and the average SNR for the electrode grid will be calculated, and pairwise comparison will be conducted between TD (SITUATION I*) and CD (SITUATION I).

The individual electrodes will be classified, per recording, as poor or good signal quality based on visual criteria (i.e., noise, flat signal due to overlap with resection cavity or silicone of secondary electrode strip, pulsation artifacts). As a result, an electrode deficiency ratio (%) will be calculated as follows: # bad electrodes divided by the total # of electrodes per recording. This will be determined for the similar positioned CD recording (SITUATION I/II) to allow comparison with the TD (SITUATION I*/I**).