Evoked Potential - Motor Evoked Potentials

Motor Evoked Potentials

Motor evoked potentials (MEP) are recorded from muscles following direct stimulation of exposed motor cortex, or transcranial stimulation of motor cortex, either magnetic or electrical. Transcranial magnetic MEP (TCmMEP) potentially offer clinical diagnostic applications. Transcranial electrical MEP (TCeMEP) has been in widespread use for several years for intraoperative monitoring of pyramidal tract functional integrity.

During the 1990s there were attempts to monitor "motor evoked potentials", including "neurogenic motor evoked potentials" recorded from peripheral nerves, following direct electrical stimulation of the spinal cord. It has become clear that these "motor" potentials were almost entirely elicited by antidromic stimulation of sensory tracts—even when the recording was from muscles (antidromic sensory tract stimulation triggers myogenic responses through synapses at the root entry level). TCMEP, whether electrical or magnetic, is the most practical way to ensure pure motor responses, since stimulation of sensory cortex cannot result in descending impulses beyond the first synapse (synapses cannot be backfired).

TMS-induced MEPs have been used in many experiments in cognitive neuroscience. Because MEP amplitude is correlated with motor excitability, they offer a quantitative way to test the role of various types of intervention on the motor system (pharmacological, behavioral, lesion...) TMS-induced MEPs may thus serve as a index of covert motor preparation or facilitation, e.g., induced by the mirror neuron system when seeing someone's else actions. In addition, MEPs are used as a reference to adjust the intensity of stimulation that need to delivered by TMS when targeting cortical regions whose response might not be as easily measurable, e.g., in the context of TMS-based therapy.

Read more about this topic:  Evoked Potential

Famous quotes containing the words motor and/or evoked:

    The motor idles.
    Over the immense upland
    the pulse of their blossoming
    thunders through us.
    Denise Levertov (b. 1923)

    The brotherhood of man is evoked by particular men according to their circumstances. But it seldom extends to all men. In the name of our freedom and our brotherhood we are prepared to blow up the other half of mankind and to be blown up in our turn.
    —R.D. (Ronald Davi)