An intracerebral electrode (11) which includes a narrow elongated body (1) for being implanted in a patient's brain. The body has contact pads (2) that are electrically connected to a measuring apparatus, and a mounting member (4) for attachment to the body to the patient's head. The electrode body has a closed distal end (5) and is hollow for receiving a treatment instrument (6). The intracerebral electrode (11) comprises a closed inner fluid flow circuit (20) formed inside the body (1) of the electrode to an area adjacent the closed distal end (5), and a connection mechanism (7) located outside the body which connects the closed inner fluid flow circuit to an outer fluid flow circuit so that fluid, flowing through the outer fluid flow circuit, flows into the electrode through the inner fluid flow circuit and controls the temperature of the electrode (11).