Operant conditioning of trigeminally-evoked cortical potentials: correlated effects on facial nociception

Effects of operantly conditioning the amplitude of the P200 peak of the SEP on pain sensitivity and the spinal nociceptive withdrawal reflex in humans

This study attempted to replicate and extend earlier work that reported that the amplitude of the P200 peak of the human somatosensory evoked potential (SEP) can be increased and decreased when reward is made contingent upon change and that these changes are accompanied by alterations in pain sensitivity. Twenty-one subjects were able to make the amplitude of the P200 peak evoked by sural nerve stimulation larger during increased training (up-training) than during decreased training (down-training). There were no differences in the sural nerve compound action potential between up-training and down-training. This finding demonstrates that the change in P200 amplitude was not due to a change in stimulus efficacy, but rather to a change within the central nervous system. Subjective pain ratings and a nociceptive spinal reflex were the same in up-training as in down-training. Thus, conditioned changes in P200 amplitude do not alter pain sensitivity.

The self-regulation of slow potential shifts and evoked potentials: interrelationships in response to somatosensory stimulation

Research on the effects of the self-regulation of event-related potentials (ERP) has failed to investigate the possible interactions and contributions of slower cortical events such as contingent negative variations (CNV) and slower DC level changes. The present study attempted to investigate such interactions by independently conditioning the ERP 200 ms poststimulus (P200) and the CNV while recording both potentials simultaneously; DC level measures were also recorded. 30 subjects attempted to increase (uptraining) or decrease (downtraining) either P200 or CNV in response to sub-painful somatosensory stimulation in a biofeedback paradigm. Following the training sessions, P200 downtrainees reported a significant decrease in their detection thresholds for the somatosensory stimuli (i.e., increased sensitivity). These results agree with some prior findings that decreased ERP amplitude in individuals is indicative of greater sensitivity in subjective pain reports. Although uptraining resulted in larger P200 amplitudes than downtraining, the difference in amplitudes between groups was not significant. CNV uptrainees achieved a higher level of pain tolerance following training. The increased CNV negativity may be associated with increased specific attentional processes that facilitate the subjects' control of, or response to, pain. CNV trainers showed a significant interaction of training over blocks of trials. Generally, there was a significant inverse correlation of P200 and CNV; as CNV amplitude became more negative, the P200 amplitude increased. DC negativity level increased over blocks for all conditions. Results indicate a complex relationship between P200, CNV and pain sensitivity. Both P200 and CNV processes are involved in pain perception, but in apparently different ways, i.e., P200 with sensitivity and CNV with tolerance.

Applied psychophysiology and biofeedback of event-related potentials (brain waves): historical perspective, review, future directions

This paper reviews the efforts of workers in the 1960s-1980s to demonstrate voluntary control of exogenously evoked (event-related) potentials in visual, somatic sensory, and auditory systems in rats, cats, and humans. The first part of the paper reviews the conceptual foundation and development of the work--it actually arose from traditional sensory coding and neural correlates of behavior studies. The second part summarizes recent applications of the method in the area of pain control. In reviewing these matters, the major effort is directed at revealing how the ideas unfolded in very human, day-to-day, anecdotal terms. There is not much of an attempt to formally review the literature, which is cited for consultation elsewhere. In the same spirit, many possible future experiments are suggested by way of elucidating the key remaining questions in the area.

Biofeedback of somatosensory event-related potentials: can individual pain sensations be modified by biofeedback-induced self-control of event-related potentials?

This study investigates the effects of biofeedback based upon event-related brain potentials evoked by nociceptive electrical stimuli. In a visual and monetary feedback paradigm, 10 subjects received positive feedback within one training session when systematically showing two different behavior patterns: one pattern correlated with a decrease (down-training) and one with an increase (up-training) of the peak-to-peak size of the N150-P260 complex, respectively. Training conditions were changed randomly from trial to trial over 300 trials. All subjects achieved control on both behavior patterns resulting in a simultaneous modification of the size of this complex according to the training conditions. Furthermore, the individual pain report measured with a visual analogue scale was altered in accordance with the biofeedback-induced behavioral modifications. A decrease in subjective pain report was achieved after down-training while an increase was observed after the up-training.

Effects of naloxone and repeated stimulus presentation on cortical somatosensory evoked potential (SEP) amplitude in the rat

The effects of naloxone (1 mg/kg) and of repeated stimulus presentation were investigated on a cortical somatosensory evoked potential elicited by innocuous stimulation of the spinal trigeminal tract in awake, minimally restrained rats. The amplitude of an early cortical component (9-ms latency) habituated after administration of saline but did not habituate after naloxone. Naloxone also enhanced the response decrement of late somatosensory evoked potential components (60 to 120 ms) produced by repeated stimulation. The amplitude of midlatency components (14 to 50 ms) did not change after administration of saline and repeated stimulus presentation. However, the amplitude of these components increased after administration of naloxone and repeated stimulus presentation.

Operant conditioning of somatosensory evoked potential (SEP) amplitude in rats. II. Associated changes in reflex and continuous non-timelocked movements

Animals were rewarded for increasing (uptrain) or decreasing (downtrain) the amplitude of a 30 ms surface positive component of a somatosensory evoked potential (SEP) evoked by innocuous stimulation of the spinal trigeminal tract. The reflex movement produced by the evoking stimulus had a larger amplitude in uptraining than downtraining. This change in reflex amplitude suggests that operantly conditioning SEP amplitude was correlated with a change in innocuous somatosensory activity. There was no change in continuous non-timelocked movement associated with conditioning. This latter finding suggests that SEP conditioning is not necessarily mediated by such movement.

Operant conditioning of somatosensory evoked potential (SEP) amplitude in rats. I. Specific changes in SEP amplitude and a naloxone-reversible somatotopically specific change in facial nociception

The aim of this experiment was to investigate possible endogenous opioid modulation of innocuous somatosensory activity. Somatosensory activity was measured by recording cortical somatosensory evoked potential (SEP) and reflex movement amplitude evoked by innocuous electrical stimulation of the spinal trigeminal tract in awake rats. Putative endogenous opioid activity was blocked using the opiate antagonist naloxone (1 mg/kg). The amplitude of midlatency SEP components (14-50 ms latency) increased following administration of naloxone and repeated stimulus presentations. The amplitude of these components decreased following administration of the opiate agonist morphine (3 mg/kg). An early cortical component (10 ms latency) habituated following the administration of saline but did not habituate following naloxone. Naloxone also enhanced habituation of the late SEP components (60-120 ms latency) and reflex movement evoked at higher stimulus intensities. Morphine decreased the amplitude of the early cortical component but had no consistent effect on the amplitude of the late SEP components.