1. A system ( 10 ) for planning a neurosurgical operation, the system ( 10 ) comprising: an input ( 11 ) for receiving functional data and anatomical data ( 25 ) of a brain region ( 31 ), and a processor ( 12 ) configured to: analyze the functional data ( 25 ) to form a network representation ( 27 ) of functional connections, the network representation ( 27 ) comprising network nodes ( 32 ) and network connections ( 41 ) interconnecting the network nodes ( 32 ), map the network representation ( 27 ) of the functional connections and the anatomical data to a common coordinate system, determine an expected function loss associated with a simulated removal of one of the network nodes ( 32 ) or network connections ( 41 ) from the network representation, and to identify critical network connections and/or critical network nodes based on the expected function loss.