Lateralized readiness potential
In neuroscience, the lateralized readiness potential (LRP) is an event-related brain potential, or increase in electrical activity at the surface of the brain, that is thought to reflect the preparation of motor activity on a certain side of the body; in other words, it is a spike in the electrical activity of the brain that happens when a person gets ready to move one arm, leg, or foot. It is a special form of bereitschaftspotential (a general pre-motor potential). LRPs are recorded using electroencephalography (EEG) and have numerous applications in cognitive neuroscience. History Kornhuber and Deecke's discovery of the Bereitschaftspotential (German for readiness potential) led to research on the now extensively used LRP, which has often been investigated in the context of the mental chronometry paradigm. In the basic chronometric paradigm, the subject experiences a warning stimulus, followed by an interval (foreperiod), and then an imperative stimulus that the subject must respond to (see chronometric paradigm). During this foreperiod, the subject may be able to prepare a unimanual response, based on information from the warning stimulus. Part of this preparation includes a slow negative wave bilaterally distributed over pre- and post-central sites, the readiness potential. Vaughan, Costa, and Ritter (1968) noted that the readiness potential was larger contralateral to the side of the body where the muscle contraction occurred. The only RPs that do not seem to be lateralized are face and tongue movements which have symmetrical distribution over both hemispheres with the maximum of the potential located in the lower half of the central sulcus. That the lateralized aspect of the readiness potential in general might be used to measure the amount of motor preparation for a direct specific action, termed "corrected motor asymmetry", was highlighted by De Jong and Gratton et al. Present-day methodology The LRP is elicited whenever a subject initiates a voluntary movement with his/her hand (or feet). Typically, a subject may be given a task requiring a button press (or squeeze) response. The LRP is recorded from the ERP over part of the motor cortex associated with the body part used to initiate the movement. The LRP is classically studied in response cuing paradigms (see cueing paradigm) and calculated by subtracting potentials recorded over the left and right side of the scalp in the motor cortex (Coles 1988). For example, if a subject were to move his or her left hand, the subsequent event related potential would be recorded over two scalp sites with the larger negativity over motor cortex on the right side of the scalp (C4) and the smaller potential over the left side of the scalp (C3). This voltage for the C3 is subtracted from C4 to yield a value that is then averaged over the course of all the subjects responses for left hand movement. The exact same procedure occurs for deriving right hand movement. The averaged potential is the LRP. The larger negativity (excluding face and tongue movements) is seen contralateral to the moving body part for all movements except