Short-term modulation of the ipsilateral primary sensory cortex by nociceptive interference revealed by SEPs.

We studied the modulation of the topographic arrangement of the human ipsilateral primary somatosensory cortex following interference of nociceptive stimuli by means of dipole source analysis. Multichannel somatosensory evoked potentials were obtained by electrical stimulation of digits 1 and 5 of the left hand before, during and after the application of pain to digits 2-4 of the right hand. The primary cortical response of the SEP (N20) was obtained for dipole localization of the representation of the primary sensory cortex receiving input from digits 1 to 5. The 3D-distance between these sides was calculated for further analysis. To account for possible attentional effects recordings were performed while simultaneously to this intervention subjects were asked to turn their attention to the right or left hand in a pseudorandom order. The application of pain induced an expansion of the 3D-distance between digits 1 and 5. Focusing attention to the stimulated limb or the site of the intervention did not yield to an additional effect. Our results provide further evidence for the presence of a quickly adapting interaction between primary somatosensory areas of both hemispheres following an interference of nociceptive stimulation in SEPs. This modifying process is probably mediated by interhemispheric and intercortical connections leading to hyperexcitability of the primary sensory cortex contralateral to that receiving nociceptive input. Spatial attention does not seem to have an impact on this kind of short-term intercortical plasticity.

The stress response in headache sufferers: physiological and psychological reactivity.

When examining headache sufferers' reactivity to stress, few studies attend to differing characteristics of the environment. In this study, we evaluated the influence of the clarity/ambiguity and positive/negative valence of an event on subjects' physiological and psychological reactivity. Migraine (n = 30), tension (n = 39), and control (n = 35) subjects participated in a laboratory experience in which they had to practice and then deliver a news story to a videocamera (similar to a newscaster on television). During this experience, they received performance feedback and were instructed to try to use the information to improve their performance. In reality, this feedback was noncontingent, with subjects semirandomly assigned to either a positive, negative, or ambiguous feedback condition. Physiological and psychological measures were collected prior to this experience, during an anticipation or practice period prior to the newscast, and during a recovery period following the delivery of the news story. Results suggested that tension subjects might not attend to information from their environment when assessing, responding, or reevaluating potentially stressful events: relying instead on more global beliefs or attributions. Results also indicated that migraine might be associated with a prolonged cardiovascular response (i.e., delayed recovery) following a stressful experience.

Prenatal exposure to AVP or caffeine but not oxytocin alters learning in female rats.

Rats whose mothers had been treated with 1 microgram of arginine vasopressin (AVP) or oxytocin (OXT), 15 mg of caffeine, or saline on days 13-19 of gestation were given training on a passive avoidance response as adults. Female rats whose mothers had been exposed to either AVP or caffeine demonstrated enhanced retention of the response. No effects were found for male rats or for exposure to oxytocin. These results suggest that prenatal exposure to AVP or caffeine produced sexually dimorphic effects on learning and that the effects are specific to the structure of AVP.