Magnetoencephalography (MEG) systems use superconducting electronics and magnetic shielding to detect the magnetic fields generated by synaptic neuronal activity. This chapter focuses on two types of quantitative analyses of human electrophysiological data: spectral analysis methods and evoked potentials. Spectral analysis of Electroencephalography (EEG) and MEG signals across multiple sensor locations reveals clear spatial patterns. EEG and MEG activity can be subdivided into three major subdivisions: spontaneous activity, evoked responses, and induced responses. Evoked responses are time domain averages across multiple trials of a repeating stimulus or response. Electroencephalographic and MEG methods based on time-frequency transformation are usually concerned with capturing changes in the brain's oscillatory phenomena produced by stimuli, mental events, or responses. A valid measure of connectivity between regions of the brain engaged in the same cognitive process or behavior is among the most highly prized uses of EEG and MEG data.

This chapter focuses on the neurotransmitter and neuromodulator systems involved in the regulation of wakefulness and sleep as well as the neurochemical responses to sleep loss. Wakefulness, rapid eye movement (REM), and non-REM (NREM) states were originally defined in mammals using measures of skull surface electrical brain activity, skeletal muscle activity, and eye movements. The two primary factors that determine the degree of human vigilance and sleepiness are the duration of prior wakefulness and circadian influences. Increases in homeostatic sleep need are associated with subjective sleepiness, objective sleepiness, diminished neurocognitive function, as well as neurochemical and neurophysiological changes. The ascending reticular activating system (ARAS) is comprised of the brainstem reticular formation and its ascending projections responsible for cortical activation and wakefulness. Electrophysiological and neurochemical data indicate that highest levels of orexinergic activity occur during active wakefulness, and greatly reduced activity is seen during NREM and REM sleep.

This chapter demonstrates how event-related potentials (ERPs) can be used to detect, isolate, and analyze functional neural modules, with special attention to functional modularity in semantic information processing. In particular, it shows how a new method of analyzing electrophysiological data, the additive-amplitude method, combines the physical property of linear superposition of electrical fields with factorial experimental design to reveal the existence of encapsulated neurocognitive modules without relying on strong assumptions. The fact that ERPs can be measured at the scalp indicates that the conditions of synchrony, spatial proximity, and parallel geometrical configuration that enable the summation of individual neuronal electric fields must hold. The additive-amplitude method yields new insights into semantic information processing architecture. Finally, it should be noted that because the additive-amplitude method focuses on a fundamental property of mind and brain, it is applicable to a broad range of areas within psychology and neuroscience.