Critical to the functioning of BattleMechs, the neurohelmet is worn by the MechWarrior inside the cockpit and connects pilot to machine. This allows the 'Mech to use its pilot's sense of balance to keep it upright.
Over time, the design of neurohelmets has changed slightly. Pre-Star League neurohelmets had outlandish designs, but were more comfortable to wear.
The neurohelmet reads the brainwaves of the pilot. The basic model of neurohelmet focuses on the human sense of balance. With a multi-ton gyroscope and powerful myomers in the limbs, BattleMechs can stand upright and remain balanced on their own, but the limited intelligence of BattleMechs and natural conservatism of their control computers means they often need to be told when it is acceptable to be off balance, which may be helpful in battle as MechWarriors push their machines. The neurohelmet also provides feedback to the MechWarrior, helping them retain their own sense of balance as they sit 10 to 12 meters in the air atop a swaying, weaving bipedal giant robot.
More advanced neurohelmets provide additional input and output beyond a sense of balance, though they never amount to "Direct Neural Interface" technology. A neurohelmet can provide the MechWarrior with a kinesthetic sense - a sense of how the 'Mech's limbs are positioned - and Star League aerospace fighter neurohelmets served to provide a weak virtual reality to the pilots. In return, MechWarriors can use neurohelmets to provide some clarification the simple commands they are supplying to a 'Mech through joysticks, triggers, and pedals.
Early neurohelmets had to be carefully calibrated to the brain of the pilot. If the calibration was not exact (or if there was the wrong pilot wearing the helmet), this could lead to a host of effects, including headache, dizzy sight, balance problems and disturbing buzzing inside your head (a very weak buzzing remains even if the calibration is correct). Such out-dated neurohelmets are still in use in Clan Sibkos and in old 'Mechs in the Periphery. Modern neurohelmets are more advanced and no longer depend on a specific pilot.
A neurohelmet can be programmed to require a code in order to use the machine it is attached to. Some example code elements include looking at various gauges for a predetermined amount of time, or moving the Mech's arms a certain way.
The neurohelmet also has a security function, as it is tuned to the specific brainwaves of the pilot. If an unauthorized individual puts on the helmet, the wearer will receive anything from simple headaches to complete unconsciousness.
 Neurohelmet in Fiction
In the Battletech novel Star Lord one of the characters notes that the Inner Sphere neurohelmet is bulkier than the Clan version. However, this could be due to the dated technology of the 'Mech in question. Many novels also state that certain injuries such as inner ear problems or brain damage prevent a person from using a neurohelmet and thus a BattleMech.