Deficient prepulse inhibition of blink reflex in migraine and its relation to allodynia

The blink reflex and its modulation - Part 2: Pathophysiology and clinical utility

The blink reflex (BR) is integrated at the brainstem; however, it is modulated by inputs from various structures such as the striatum, globus pallidus, substantia nigra, and nucleus raphe magnus but also from afferent input from the peripheral nervous system. Therefore, it provides information about the pathophysiology of numerous peripheral and central nervous system disorders. The BR is a valuable tool for studying the integrity of the trigemino-facial system, the relevant brainstem nuclei, and circuits. At the same time, some neurophysiological techniques applying the BR may indicate abnormalities involving structures rostral to the brainstem that modulate or control the BR circuits. This is a state-of-the-art review of the clinical application of BR modulation; physiology is reviewed in part 1. In this review, we aim to present the role of the BR and techniques related to its modulation in understanding pathophysiological mechanisms of motor control and pain disorders, in which these techniques are diagnostically helpful. Furthermore, some BR techniques may have a predictive value or serve as a basis for follow-up evaluation. BR testing may benefit in the diagnosis of hemifacial spasm, dystonia, functional movement disorders, migraine, orofacial pain, and psychiatric disorders. Although the abnormalities in the integrity of the BR pathway itself may provide information about trigeminal or facial nerve disorders, alterations in BR excitability are found in several disease conditions. BR excitability studies are suitable for understanding the common pathophysiological mechanisms behind various clinical entities, elucidating alterations in top-down inhibitory systems, and allowing for follow-up and quantitation of many neurological syndromes.

Modulation of the Somatosensory Blink Reflex in the Peripersonal Space Is Defective in Episodic Migraine

OBJECTIVE

In migraine, there is an altered behavior of patients during the attack and an altered connectivity in the cortical structures modulating and encoding the sensation and pain. Thus, we hypothesized that the extent of the peripersonal space (PPS) and the responses in the PPS may change during a migraine attack. For this reason, we analyzed the modulation of somatosensory blink reflex (SBR) in the PPS during episodic migraine.

DESIGN

Cross-sectional assessment of modulation of SBR in patients with migraine.

SETTING

Headache outpatient clinic of a tertiary referral center.

SUBJECTS

We included 22 patients with episodic migraine, of whom 13 individuals were in the interictal period and nine were experiencing a headache episode. We also included 14 healthy individuals. The three groups were similar in age and gender.

METHODS

SBR was recorded when the participants were sitting with their forearm in the extrapersonal space and also when their hands were in the PPS surrounding the face. Latency, amplitude, and area under the curve (AUC) were measured and compared.

RESULTS

The amplitude and AUC of the SBR were significantly higher in patients during the attack compared with healthy subjects. The magnitude of the SBR was increased in the PPS in healthy subjects, whereas the increase was not significant in patients during the attack or in the interictal period.

CONCLUSIONS

We think that the modulation in the PPS is defective in patients with migraine both during the acute attack and in the interictal phase, suggesting diminished top-down modulation of the SBR.

Focus on the pedunculopontine nucleus. Consensus review from the May 2018 brainstem society meeting in Washington, DC, USA

The pedunculopontine nucleus (PPN) is located in the mesopontine tegmentum and is best delimited by a group of large cholinergic neurons adjacent to the decussation of the superior cerebellar peduncle. This part of the brain, populated by many other neuronal groups, is a crossroads for many important functions. Good evidence relates the PPN to control of reflex reactions, sleep-wake cycles, posture and gait. However, the precise role of the PPN in all these functions has been controversial and there still are uncertainties in the functional anatomy and physiology of the nucleus. It is difficult to grasp the extent of the influence of the PPN, not only because of its varied functions and projections, but also because of the controversies arising from them. One controversy is its relationship to the mesencephalic locomotor region (MLR). In this regard, the PPN has become a new target for deep brain stimulation (DBS) for the treatment of parkinsonian gait disorders, including freezing of gait. This review is intended to indicate what is currently known, shed some light on the controversies that have arisen, and to provide a framework for future research.

Reduced inhibition in brainstem circuits in classical trigeminal neuralgia

OBJECTIVE

We hypothesized that prepulse modulation (PPM) would be altered in trigeminal neuralgia (TN) if suprasegmental inhibitory network involvement was present and tested our hypothesis in a group of patients with classical TN.

METHODS

The study enrolled nine consecutive patients with classical TN and 14 healthy subjects. Diagnosis and classification followed the International Classification of Headache Disorders-third edition (beta version). The blink reflex (BR) and BR-PPM were recorded. Ipsilateral recordings were made after stimulating each trigeminal nerve in the patient group whereas right-sided recordings were performed after stimulating the right trigeminal nerve in the healthy subjects. A conditioning electrical stimulus was applied to the ipsilateral median nerve at interstimulus intervals (ISIs) of 50 and 100 ms before the test stimulus to the supraorbital nerve.

RESULTS

The unconditioned BR recordings were similar in all groups. In the healthy subjects, the prepulse stimulus resulted in a reduced R2 magnitude (p = 0.000, Friedman's test) and longer R2 latency (p = 0.008, Friedman's test) at ISIs of 50 and 100 ms in comparison with unconditioned recordings. The R2 latency differed significantly between the unconditioned recordings and the ISI of 100 ms. In the patients with TN, no significant change was observed on either the symptomatic or asymptomatic sides.

CONCLUSIONS

There is a bilateral prepulse inhibition deficit in TN, even on the asymptomatic side. Our findings provide electrophysiological evidence for suprasegmental changes and loss of filtering activity at the brainstem in level TN.

Differential modulation of prepulse inhibition of the blink reflex in peripersonal versus extrapersonal space

OBJECTIVE

Threatening stimuli encountered in peripersonal space (PPS) are processed differently from those encountered in extrapersonal space (EPS). This phenomenon is attributed to tonic top-down modulation. We hypothesized that prepulse inhibition (PPI) of a reflex, which has a protective function, may change according to whether the conditioning stimulus appears in PPS or EPS. We aimed to compare the strength of the PPI according to whether stimulation was delivered in PPS or EPS.

METHODS

The study included 23 healthy subjects with a mean age of 36.8±9.1years. Recordings of blink reflex (BR) after supraorbital stimulation (so-BR) were performed. Recordings of BR after prepulse stimulation to the median nerve 100ms prior to the supraorbital stimulation were acquired with the ipsilateral hand 50-60cm from the face (EPS) and approximately 3-4cm from the face (PPS). Changes of response magnitudes were compared between PPS and EPS conditions.

RESULTS

R2 area-under-the curve of so-BR was reduced after prepulse stimulation of median nerve in all subjects while the hand was in EPS. Although the R2 magnitude was also decreased after prepulse stimulation while the hand was in PPS, the percentage of reduction with the hand in PPS was significantly smaller compared to that with the hand in EPS.

CONCLUSION

Reduction in R2 magnitude after prepulse stimulation 100ms prior to test pulse is recognized (PPI). Although PPI was observed under both conditions, PPI of so-BR was attenuated when the stimulus was presented in the PPS. Therefore, our study provides evidence for modulation of PPI of so-BR in PPS and may suggest top-down modulation of the neural circuitry underlying PPI.