Objective: To assess the influence of directed attention on prepulse inhibition (PPI) of the blink reflex in patients with functional movement disorders (FMD) and healthy controls.

Background: PPI is a neurophysiological phenomenon in which a weak sensory stimulus (prepulse), subthreshold for eliciting any reflex response, leads to reduction in magnitude of the reflex response elicited by a strong stimulus presented 30-500 ms later.  PPI at interstimulus interval (ISI) of 100 ms, reflecting an early stage of attentional processes and somatosensory integration at subcortical level, has been shown abnormal in FMD[1]. In contrast to PPI at ISI 100 ms, PPI size at longer ISI is smaller and can be enhanced by attention voluntarily directed at the prepulse[2]. We hypothesized the attentional modulation of PPI might be disrupted in FMD.

Method: We examined the effect of a weak electrical stimulus to the index finger (prepulse) on the blink reflex magnitude induced by electrical stimuli delivered to the supraorbital nerve at ISI 100 and 240 ms in 26 patients with clinically established FMD (14 females, age=40.4±12.5 years, illness duration=4.4±2.6 years) and 24 healthy control subjects (14 females, age=42.0±9.5 years). The PPI at 240 ms ISI was assessed in relaxed condition and with attention directed towards the prepulse. All subjects provided self-reported measures of pain, depression, anxiety, and cognitive complaints.

Results: Reflex response was reduced by 46.9±23.8% in patients and by 59.0±18.3% in controls (p<0.05) at ISI 100 ms.  There was no between-group difference observed at ISI 240 ms (with or without directed attention towards the prepulse). There was no significant correlation between non-motor symptom measures and PPI size.

Conclusion: This study replicated previous findings of impaired PPI of the blink reflex in FMD suggestive of an abnormal pre-conscious processing of somatosensory inputs at the early subcortical stage of attentional processes involved in information selection processing. We did not find between-group differences in modulatory effect of voluntarily allocated attention to a sensory stimulus.  Larger cohorts will be necessary to elucidate the role of top-down attentional effects on PPI in FMD.

References: [1] Z. Hanzlikova, M. Kofler, M. Slovak, G. Vechetova, A. Fecikova, E. Ruzicka, J. Valls-Sole, M. Edwards, T. Serranova, Abnormal prepulse inhibition of the blink reflex in functional movement disorders, Eur. J. Neurol. 26 (2019) 643-643.
[2] K. Heekeren, U. Meincke, M.A. Geyer, E. Gouzoulis-Mayfrank, Attentional modulation of prepulse inhibition: a new startle paradigm, Neuropsychobiology 49(2) (2004) 88-93.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/prepulse-inhibition-of-the-blink-reflex-in-functional-movement-disorders/