During surgery, electrophysiological signals will be acquired with the instrument (ISIS IOM, NeuroExplore, Software Version 4.4, Inomed) already in use at the Neurosurgery Service of the Neurocentro of the Hospital Civic Italian Switzerland in Lugano. Simultaneously to Somatosensorial Evoked Potential (SEP) will also be recorded the Electroencephalography (EEG) activity with the same detection of locations.

For the purposes of the study the signals transmitted to the neurosurgeon through the hardware and the corresponding assessments done by the neurophysiologist responsible for intraoperative monitoring will be recorded. It will also be kept track of procedures performed during surgery.

Inclusion Criteria:

• Age ≥ 18 years old
• Patient bearer of a not broken cerebral aneurysm, which has been defined per size and morphology susceptible to surgery
• Aneurysms located on cerebral arteries of the anterior circulation (carotid, middle cerebral arteries, anterior cerebral, anterior communicating, pericallose); Cases of multiple aneurysms are also eligible
• Informed consent for participation in the study

Exclusion Criteria:

• Patient with an aneurysm of the posterior circulation (vertebrobasilar system)
• The aneurysm was a source of bleeding (subarachnoid hemorrhage, intracerebral, intraventricular).
• Patient with a pace-maker (for the risk that the electric currents used in the study could compromise the operation of the pace-maker)

Patient bearer of a not broken cerebral aneurysm