Laser-evoked potentials: exogenous and endogenous components |
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Institution: | 1. Department of Biophysics, Faculty of Medicine, Firat University, Elazig, Turkey;2. Department of Physiology, Faculty of Medicine, Firat University, Elazig, Turkey;1. Near East University, Medical Faculty, Department of Medical Genetics, Lefkosa, Mersin 10, Turkey;2. Near East University, Art and Sciences Faculty, Department of Molecular Biology and Genetics, Lefkosa, Mersin 10, Turkey Lefkosa, Mersin 10, Turkey;3. Telomere Aging Group, Center for IRS, Southern Denmark University, 7100 Vejle, Denmark;4. Marmara University, School of Medicine, Biophysics Department, Istanbul, Turkey;1. Department of Neonatology, La Paz University Hospital, Madrid, Spain;2. Center for Biomedical Technology, Technical University, Madrid, Spain;3. Biomedical Research Foundation, La Paz University Hospital, Madrid, Spain;4. Biomedical Research Networking Center in Bioengineering Biomaterials and Nanomedicine (CIBER-BBN), Zaragoza, Spain;5. Division of Statistics, La Paz University Hospital, Madrid, Spain |
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Abstract: | The aim of this study was to distinguish the exogenous component (related to the physical properties of the stimulus) and the endogenous component (reflecting event-related cognitive processing) of the laser-evoked potential (LEP). Short painful radiant heat pulses generated by a CO2-laser were applied to the dorsum of the right and left foot. LEPs were recorded with 5 scalp electrodes in the midline versus linked earlobes in 26 healthy subjects. In order to identify the exogenous component, the LEP was recorded during a standardised distraction task (reading a short story). To identify the endogenous component P3 for the LEP, a 2-stimulus oddball paradigm was used (20% probability of targets). When the task of the oddball paradigm consisted of pressing a button, a movement-related long-latency negativity (N1200) was recorded in frontal leads that was absent in a counting task. The LEP of targets, frequent non-targets and during distraction was dominated by a single large positivity. The amplitude of this positivity was task-dependent and increased the more attention the subject payed to the laser stimuli (distraction < neutral < non-target < target). The laser-evoked positivity during distraction had a peak latency of about 400 msec (P400) and a maximum amplitude at the vertex, which was independent of inter-stimulus interval. The P3 following laser stimulation had a significantly later peak at about 570 msec (P570) and a different scalp topography with a parietal maximum. Its amplitude decreased when the interstimulus interval was reduced from 10 to 6 sec. Under neutral instructions, the LEP positivity consisted of a superposition of both the exogenous P400 and the endogenous P570. |
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