One of the reasons for that struggling may be that, while experimental science is supposed to be precise, the literature search at the beginning is often relatively ill defined, with fuzzy boundaries. The notion of the fourth grade slump has been discussed in the reading literature for decades, and has also been considered in the education literature and popular press. Event-related potentials (ERPs) are recorded non-invasively at the scalp, and reflect the stimulus-locked information processing activities of large assemblies of neurons in different areas of the brain, providing a real-time neural recording. The N400 is a negative-going deflection in the ERP waveform that peaks on average at about 400 milliseconds after presentation of a stimulus. One millisecond is one one-thousandth of one second. From a neuroscience perspective, given the many components involved in reading, it is not surprising that there is no one part of the brain that "does" reading. Indeed, there is really no "reading brain" at all.