Electroencephalography (EEG) is the measurement of electrical activity produced by the brain as recorded from electrodes placed on the scalp.

Just as the activity in a computer can be understood on multiple levels, from the activity of individual transistors to the function of applications, so can the electrical activity of the brain be described on relatively small to relatively large scales. At one end are action potentials in a single axon or currents within a single dendrite of a single neuron, and at the other end is the activity measured by the EEG which aggregates the electric voltage fields from millions of neurons. So-called scalp EEG is collected from tens to hundreds of electrodes positioned on different locations at the surface of the head. EEG signals (in the range of milli-volts) are amplified and digitalized for later processing. The data measured by the scalp EEG are used for clinical and research purposes. In neurology, the main diagnostic application of EEG is for epilepsy but this technique is also used to investigate many other pathologies such as sleep-related disorders, sensory deficits, brain tumors, etc. In cognitive neuroscience, EEG is used to investigate the neural correlates of mental activity from low-level perceptual and motor processes to higher-order cognition (attention, memory, reading, etc).

In some cases, such as epileptic studies, when deeper brain activity needs to be recorded with more accuracy than provided by scalp EEG, clinicians use an invasive form of EEG known as intracranial EEG (icEEG) where electrodes are placed directly inside the skull. In some cases, a grid of electrodes is laid on the external surface of the brain, on dura mater yielding epidural EEG but in other cases, brain activity is recorded using deeper electrodes...

Meditation is a mental discipline by which one attempts to get beyond the conditioned, "thinking" mind into a deeper state of relaxation or awareness. Meditation often involves turning attention to a single point of reference. It is recognized as a component of almost all religions, and has been practiced for over 5,000 years.The Bhagavad-Gita and Jivana Yoga By Ramnarayan VyasHatha Yoga: Its Context, Theory and Practice By Mikel BurleyZen Buddhism: A History (India and China) By Heinrich Dumoulin, James W. Heisig, Paul F. Knitter It is also practiced outside religious traditions. Different meditative disciplines encompass a wide range of spiritual and/or psychophysical practices which may emphasize different goals -- from achievement of a higher state of consciousness, to greater focus, creativity or self-awareness, or simply a more relaxed and peaceful frame of mind.

The word meditation originally comes from the Indo-European root med-, meaning "to measure."Take Our Word For it Archive of Etymology Questions: MediationAmerican Heritage Dictionary: List of Indo European Roots From the root med- are also derived the English words mete, medicine, modest, and moderate. It entered English as meditation through the Latin meditatio, which originally indicated every type of physical or intellectual exercise, then later evolved into the more specific meaning "contemplation."

Eastern meditation techniques have been adapted and increasingly practiced in Western culture.