Enhanced blink reflex recovery in juvenile myoclonic epilepsy

Spontaneous, Voluntary, and Reflex Blinking in Clinical Practice

Blinking is one of the motor acts performed more frequently by healthy human subjects. It involves the reciprocal action of at least two muscles: the orbicularis oculi shows a brief phasic activation while the levator palpebrae shows transient inhibition. In clinical practice, noninvasive recording of the orbicularis oculi activity is sufficient to obtain useful information for electrodiagnostic testing. Blinking can be spontaneous, voluntary, or reflex. Although the analysis of spontaneous blinks can already furnish interesting data, most studies are based on reflex blinking. This article is a review of some of the alterations that can be observed in blinking, focusing in four patterns of abnormality that can be distinguished in the blink reflex: (1) afferent versus efferent, which allows characterization of trigeminal or facial lesions; (2) peripheral versus central, which distinguishes alterations in nerve conduction from those involving synaptic delay; (3) upper versus lower brainstem lesions, which indicates the lesions involving specific circuits for trigeminal and somatosensory blink reflexes; and (4) asymmetric abnormal excitability pattern, which shows a unilateral alteration in the descending control of excitability in brainstem circuits. The blink reflex excitability recovery curve to paired stimuli may provide information about other modulatory inputs to trigemino-facial circuits, such as those proposed for the connection between basal ganglia and trigeminal neurons. Finally, prepulse inhibition of blink reflex reflects the motor surrogate of subcortical gating on sensory volleys, which is still another window by which electrodiagnosis can document motor control mechanisms and their abnormalities in neurologic diseases.

Role of mesial temporal lobe structures in sensory processing in humans: a prepulse modulation study in temporal lobe epilepsy

Prepulse modulation (PPM) is an electrophysiological method which enables to assess sensory processing in vivo. Reflex responses may be facilitated or inhibited (prepulse inhibition, PPI) after a weak stimulus. Theoretically, in animal studies, the generator of PPI involves pedunculopontine nucleus which is modulated by various structures, including amygdala. We aimed to investigate whether or not there was a role of limbic structures in the generation of PPM in humans. For this purpose, we studied PPM of the blink reflex (BR) in 10 patients with mesial temporal lobe epilepsy (MTLE group) and in nine patients who had previously undergone amygdala resection for medically resistant MTLE (surgery group). A control group including 19 healthy volunteers was formed. Blink reflex, BR-PPM and BR excitability recovery were recorded in all participants. Two components of BR, first early ipsilateral component (R1) and second late bilateral components (R2 and R2c) were identified. All BR parameters after single stimulation were normal in all groups. Compared to healthy subjects, R2-PPI was more pronounced in the surgery group whereas there was a R2-PPI deficit in the MTLE group. R2-PPI deficit in the MTLE group was more prominent on the lesion side. Ipsilesional R1 facilitation was more evident at ISI of 100 ms in both MTLE and surgery groups compared to healthy subjects. BR excitability recovery was not different between groups. MTLE in humans leads to a PPI deficit. Interestingly, removal of amygdala in humans with MTLE probably provides more efficient functioning of PPI network. Amygdala and hippocampus play roles in the human R2-PPI circuit. Modulation of R1 facilitation is unilateral whereas the modulation of R2-PPI is bilateral, though asymmetric.