ES2 Duration Research Articles

Exteroceptive Suppression Periods in Jaw-Closing Muscles. Variability and Relation to Experimental Pain and Sustained Muscle Contraction

The duration of the late exteroceptive suppression period (ES2) of temporal muscle EMG activity has been reported to be reduced in patients suffering from chronic tension-type headache. Methods of recording and analysing ES2 have varied between centers and reproducibility of results within subjects, although insufficiently studied, has generally been poor. ES2 was investigated in 30 healthy subjects, using a computerized technique of recording, rectifying and averaging the EMG signals. Hour to hour and week to week variations of ES2 durations were calculated, and the influence of pain during a cold pressor test and of sustained muscle contraction on ES2 durations was investigated. The intra-individual variation of ES2 durations was 16.0% from hour to hour and 20.7% from week to week. The inter-individual variation was 36.7%. The present method for analysis of ES2 periods proved to be reliable, as the intra-observer variation was 4.2% and the inter-observer variation 4.6%. ES2 periods were significantly shorter on the first compared to the second day of examination (p = 0.006) and during experimental pain (p = 0.0005). We recommend the use of the computerized average technique in future studies and caution against the dependence of results upon factors such as conditioning and pain.

Wolff Award 1992. Exteroceptive suppression of temporalis muscle activity in patients with chronic headache and in normal volunteers: methodology, clinical and pathophysiological relevance.

Exteroceptive suppression of temporalis muscle activity was studied in patients with chronic headache and in healthy controls. Among different methods of recording, averaging 10 full-wave rectified EMG responses produces results with acceptable variability and discomfort. The late temporalis exteroceptive suppression period (ES2) is reduced on average in patients with chronic tension-type headache; this finding has been reproduced by several independent laboratories. Mean duration of temporalis ES2 is also diminished, but to a lesser degree, in daily drug abuse headache and, as shown by others, in episodic tension-type headache. It is normal in migraine between attacks, cluster headache and various types of symptomatic headaches. Temporalis ES2 may be decreased in untreated patients with major depression. In healthy volunteers, temporalis ES2 duration is reduced by a short-lasting painful stimulus to peripheral limbs after a delay of 50 to 60 ms, and by a sub-motor threshold electromagnetic stimulation to the contralateral cerebral cortex after a delay of 20 to 30 ms. In contrast, long-lasting trains of peripheral painful stimuli have no effect. Various pharmacological agents are able to modify temporalis ES2. Its duration is increased by 5-HT antagonists, but decreased by 5-HT uptake blockers. Pharmacological effects may differ between controls and patients. Considering these results and available data on the anatomo-functional organization of masticatory reflexes, we postulate that temporalis ES2 is a marker of the excitability of interneuronal nets in the ponto-medullary reticular formation. In chronic tension-type headache, excitability of these interneurons is decreased because of inadequate control by the serotonergic raphe magnus nucleus and the periaqueductal gray matter. Dysfunctioning of the latter structures might be caused by abnormal limbic inputs to the brain stem. Some steps of this pathophysiological hypothesis can be verified by modern neurophysiological techniques.

Acetylsalicylic acid activates antinociceptive brain-stem reflex activity in headache patients and in healthy subjects

The exteroceptive suppression (ES) of electrical activity in the temporal muscle is an inhibitory antinociceptive brain-stem reflex. We investigated whether aspirin can significantly modulate latencies or durations of the early (ES1) and late (ES2) exteroceptive suppression periods of electrical activity in the temporal muscle. Participating in the randomized double-blind crossover study were 20 patients with migraine without aura, 20 patients with tension-type headache, and 20 healthy subjects. ES1 and ES2 elicited by an electrical stimulus of 20 mA lasting 0.2 msec were recorded during maximal voluntary contraction of the mastication muscles before and 30 min after medication. In a randomized and double-blind fashion half of the subjects were given 1200 mg of aspirin in the form of an effervescent solution and the other half were given an identically tasting solution without aspirin. One week later the experiment was repeated with the substances exchanged in crossover fashion. The administration of placebo as well as aspirin caused a highly significant increase in ES1 duration ( P⩽ 0.001). While aspirin caused a highly significant increase in ES2 duration ( P < 0.001) the taking of placebo showed no significant effect on ES2 duration. In giving aspirin as opposed to the placebo, there was a significant interaction between groups and drug effect on the latency of ES1; whereas in migraine patients and in patients with tension-type headache the latency of ES1 was reduced by administration of aspirin, it was increased in healthy subjects ( P ⩽ 0.05). Neither aspirin nor placebo significantly varied the ES2 latency. The results indicate that aspirin and placebo influence antinociceptive functions of the brain-stem. Beyond the placebo effect aspirin is also able to activate complex pain control mechanisms as the polysynaptically mediated ES2. Finally in patients who suffer from migraine or tension-type headache, these pain control mechanisms appear to have partially other functional characteristics than in healthy individuals.

Exteroceptive Silent Period of Temporalis Muscle in Menstrual Headaches

The second exteroceptive silent period (ES2) of temporalis muscle was recorded on days 1 and 15 of the menstrual cycle in 17 women, 9 of whom suffered regularly from tension-type headaches during menstruation. Mean duration of temporalis ES2 was significantly shorter on day 1 of the cycle than on day 15. This difference was due to a marked menstrual reduction of ES2 in the headache subgroup. A positive correlation was found between ES2 durations and oestradiol/progesterone ratios. We hypothesize that the variations of ES2 during the ovarian cycle result from the modulatory effects of oestrogens on descending aminergic pathways that control excitability of inhibitory brainstem interneurons mediating exteroceptive suppression of jaw-closing motoneurons.