Comparison of touch- and laser heat-evoked cortical field potentials in conscious rats
Journal
Brain Research
Journal Volume
824
Journal Issue
2
Pages
183-196
Date Issued
1999
Date
1999
Author(s)
Abstract
Field potentials and multiunit activities from chronically implanted cortical electrodes were used to study tactile and nociceptive information processing from the tail of the rat. Fourteen stainless steel screws implanted in the skull were used as electrodes to record field potentials in different cortical areas. Electrical, mechanical, and laser pulses were applied to the tail to induce evoked cortical field potentials. Evoked responses were compared before and after sodium pentobarbital anesthesia (50 mg/kg, i.p.). In both electrical- and mechanical-evoked potential (EEP and MEP) studies, two major peaks were found in the conscious animal. The polarity of the late component was modified after pentobarbital anesthesia. In the laser-evoked potential (LEP) study, two distinct negative peaks were found. Both peaks were very sensitive to anesthesia. Following quantitative analysis, our data suggest that the first positive peak of EEP and MEP corresponded to the activation of the Aβ fiber, the second negative peak of MEP and the first peak of LEP corresponded to Aδ fiber activation, while the second peak of LEP corresponded to C fiber activation. The absolute magnitudes of all cortical components were positively related to the intensity of the stimulation. From spatial mapping analysis, a localized concentric source of field potential was observed in the primary somatosensory cortex (SI) only after activation of the Aβ fiber. Larger responsive cortical areas were found in response to Aδ and C fiber activation. In an intracortical recording experiment, both tactile and nociceptive stimulation evoked heightened unit activity changes at latencies corresponding to respective field potentials. We conclude that different cortical areas are involved in the processing of A and C fiber afferent inputs, and barbiturate anesthesia modifies their processing.
Subjects
A fiber; C fiber; Electrical stimulation; Nociception; Somatosensory function; Topographical mapping
Other Subjects
afferent nerve group 1; animal experiment; animal model; animal tissue; article; brain cortex; brain mapping; electric potential; electrostimulation; evoked cortical response; male; nerve fiber c; nociception; nociceptive stimulation; nonhuman; priority journal; rat; sensory nerve; somatosensory cortex; tactile stimulation; Afferent Pathways; Animals; Brain Mapping; Cerebral Cortex; Electric Stimulation; Evoked Potentials; Heat; Lasers; Male; Nerve Fibers; Rats; Rats, Wistar; Stress, Mechanical; Touch
Type
journal article
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