Temporary removal of a portion of the skull to allow the removal or debulking of a tumour, brain biopsy or drainage of a cerebral abscess. The skull portion is usually re-inserted at the end of surgery. Carrying out the operation awake allows the intra-operative assessment of a patients neurological function, in particular their speech. Indications are epilepsy, excision of tumours close to the brain's speech centres. Awake means that patients are typically anaesthetised (being asleep) for the start of the operation, woken up during the critical period to allow for the assessment, then re-anaesthetised for the end of the operation. Occasionally the whole procedure is carried out with sedation and local anaesthesia instead of a general anaesthetic.