Operant conditioning of trigeminal nuclear evoked potentials

Enhanced nociceptive behaviour following conditioning injection of formalin in the perioral area of the rat

The possible existence of long-term modifications in response to a transient nociceptive conditioning stimulation was investigated in the rat in three experiments. (1) A nociceptive conditioning stimulus was delivered in the form of a s.c. formalin injection (conditioning injection) in the left upper lip. Evaluation of the nociceptive behaviour triggered by another formalin injection (testing injection) made in the controlateral right upper lip was carried out in distinct groups of rats 7, 14 or 28 days after the conditioning. An enhanced nociceptive response at day 7 and 14 and a return to the baseline at day 28 were observed. (2) A similar protocol was developed with formalin used for both conditioning and testing but an anaesthetic blockade of the infraorbital nerve was performed just before the conditioning injection to suppress the initial barrage. The change observed at day 7 was suppressed by the nerve block. (3) A conditioning nociceptive stimulus was applied either ipsilaterally to the right lower lip or to the tail. An increased nociceptive response was observed when the conditioning stimulus was applied to the same side as the test stimulus but no increase in the formalin test response was detected when the conditioning stimulus was applied to the tail. These results indicated that, after a single formalin injection in the left upper lip, a hyperexcitability developed that depended on the initial barrage, lasted for at least 2 weeks, was no longer present at 4 weeks and might rely on a segmental mechanism. The hypothesis of a central sensitization triggered by an initial barrage and maintained by an ongoing input induced from the periphery is discussed.

Sustained hyperalgesia can be induced in the rat by a single formalin injection and depends on the initial nociceptive inputs

The present study was undertaken to find out if a hyperalgesia can be observed 1 week after a conditioning stimulation of the orofacial area of the rat. Sprague-Dawley rats received a left infraorbital infiltration with either bupivacaine or saline and then, 30 min thereafter, an injection of either saline or 10% formalin solution in the left upper lip. Four groups of animals were thus made up depending on their conditioning treatment. Seven days later, an algesimetric test initiated by a contralateral orofacial formalin injection was carried out. The duration of lip rubbing was significantly increased in formalin-conditioned groups. The hyperalgesia observed at 7 days was suppressed by an infraorbital nerve block carried out at the time of the conditioning stimulus. These results tend to indicate that a nociceptive message of short duration induces a trace in the central nervous system which can be retained for 1 week.

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.

Operant conditioning of the short-latency cervical somatosensory evoked potential in quadriplegics

Operant conditioning of short-latency cervical somatosensory evoked potentials (CSEP) was demonstrated in five cervical cord injury subjects. Subjects were conditioned to augment the N14 potential, thought to originate from the dorsal column nucleus. Increased N14 potential was associated with an increase in N19 and P22 potentials, and either a decrease (base) or no change (train) in the brachial plexus potential. The N19 potential was correlated with significant reductions in the sensation-twitch (S/T) ratio during conditioning sessions, indexing improved sensation to low-intensity percutaneous stimulation. Moreover, S/T ratios decreased significantly during conditioning sessions, and were reduced significantly relative to initial baseline values. The results do not appear to be associated with trivial mediating influences.