Neurophysiology is the study of nerve cells (neurones) as they receive and transmit information. It is a branch of physiology and neuroscience that focuses on the functioning of the nervous system. The word originates from the Greek word νεῦρον meaning "nerve" and physiology meaning knowledge about the function of living systems (φύσις meaning "nature" and -λογία meaning "knowledge"). Studies of neurophysiology emerged as early as 4000 BCE. During this time period, the focus was to better understand the nervous system through the brain and spinal cord and the connection it has with mental health. Currently methods used to utilise the research of neurophysiology include electrophysiological recordings, such as patch clamp, voltage clamp, extracellular single-unit recording and recording of local field potentials.