Evoked fields are part of the

magnetoencephalogram Magnetoencephalography (MEG) is a functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers. Arrays of SQUIDs ...

. They are brain signals evoked by sensory

stimulation Stimulation is the encouragement of development or the cause of activity generally. For example, "The press provides stimulation of political discourse." An interesting or fun activity can be described as "stimulating", regardless of its physica ...

, but usually buried by the ongoing brain activity. Repeating the stimulus multiple times and averaging the signals reduces the uncorrelated ongoing activity and reveals the evoked field. Evoked fields are the magnetoencephalographic equivalent to

evoked potential An evoked potential or evoked response is an electrical potential in a specific pattern recorded from a specific part of the nervous system, especially the brain, of a human or other animals following presentation of a Stimulus (physiology), stimu ...

s, which are part of the

electroencephalogram Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...

Auditory evoked fields

An auditory evoked field (AEF) is a form neural activity that is induced by an auditory stimulus and recorded via

magnetoencephalography Magnetoencephalography (MEG) is a functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers. Arrays of SQUIDs (su ...

, which is an equivalent of

auditory evoked potential An evoked potential or evoked response is an electrical potential in a specific pattern recorded from a specific part of the nervous system, especially the brain, of a human or other animals following presentation of a stimulus such as a light fla ...

(AEP) recorded by

electroencephalography Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...

. The advantage of AEF over AEP is the powerful spatial resolution provided by

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

recording, which AEP lacks. Thus, researchers using AEF often deals with the global responses of the whole brain at the cortical level while focusing on the role of the auditory pathway. The common applications of AEF are

prenatal Prenatal development () includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal devel ...

and

neonatal An infant or baby is the very young offspring of human beings. ''Infant'' (from the Latin word ''infans'', meaning 'unable to speak' or 'speechless') is a formal or specialised synonym for the common term ''baby''. The terms may also be used to ...

hearing screening, cortical pitch perception, language comprehension, and attention.

Sources and types of responses

The main source of the auditory evoked field is the

auditory cortex The auditory cortex is the part of the temporal lobe that processes auditory information in humans and many other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations to ...

and the association cortices. The earliest cortical components of AEF is equivalent to the ''middle latency response'' (MLR) of the EEG evoked potential, called the ''middle latency auditory evoked field'' (MLAEF), which occurs at 30 to 50 ms after the stimulus onset. M30 and M50, occurring at 30 and 50 ms after the stimulus onset, correspond to the ''Pa'' and ''Pb'' peaks of MLR. The M50 response was often used to study the correlation of aging and hearing loss. Research has shown that the amplitude of

contralateral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

M50 enlarges with age. At 100 ms after stimulus onset occurs the most prominent response in the late latency range, the M100, which corresponds to the N1 peak of the ''auditory long latency response'' (ALR) potential. M100 is the most widely used magnetic field response clinically. In 2007, Lütkenhöner ''et al.'' demonstrated that M100 can be applied to estimate hearing threshold to a higher degree of accuracy. Longer latency responses after 100 ms are referred as

event-related field An event-related potential (ERP) is the measured brain response that is the direct result of a specific sensory, cognitive, or motor event. More formally, it is any stereotyped electrophysiological response to a stimulus. The study of the brai ...

(ERF) that includes M150, M200, M300 (equivalent of P300), and M400.Simos PG, Basile LF, Papanicolaou AC. Source localization of the N400 response in a sentence-reading paradigm using evoked magnetic fields and magnetic resonance imaging. Brain Res. 1997 Jul 11;762(1-2):29-39.

References

{{DEFAULTSORT:Evoked Field Evoked potentials Magnetoencephalography Neurophysiology

Auditory evoked fields

Sources and types of responses

See also

References