A high-resolution binocular video-oculography system: assessment of pupillary light reflex and detection of an early incomplete blink and an upward eye movement

Background: The pupillary light reflex characterizes the direct and consensual response of the eye to the perceived brightness of a stimulus. It has been used as indicator of both neurological and optic nerve pathologies. As with other eye reflexes, this reflex constitutes an almost instantaneous movement and is linked to activation of the same midbrain area. The latency of the pupillary light reflex is around 200 ms, although the literature also indicates that the fastest eye reflexes last 20 ms. Therefore, a system with sufficiently high spatial and temporal resolutions is required for accurate assessment. In this study, we analyzed the pupillary light reflex to determine whether any small discrepancy exists between the direct and consensual responses, and to ascertain whether any other eye reflex occurs before the pupillary light reflex. Methods: We constructed a binocular video-oculography system two high-speed cameras that simultaneously focused on both eyes. This was then employed to assess the direct and consensual responses of each eye using our own algorithm based on Circular Hough Transform to detect and track the pupil. Time parameters describing the pupillary light reflex were obtained from the radius time-variation. Eight healthy subjects (4 women, 4 men, aged 24–45) participated in this experiment. Results: Our system, which has a resolution of 15 microns and 4 ms, obtained time parameters describing the pupillary light reflex that were similar to those reported in previous studies, with no significant differences between direct and consensual reflexes. Moreover, it revealed an incomplete reflex blink and an upward eye movement at around 100 ms that may correspond to Bell’s phenomenon. Conclusions: Direct and consensual pupillary responses do not any significant temporal differences. The system and method described here could prove useful for further assessment of pupillary and blink reflexes. The resolution obtained revealed the existence reported here of an early incomplete blink and an upward eye movement.

Botulinum Toxin as an Alternative to Treat the Spasm of the Near Reflex

We describe the case of an eight-year-old girl with complaints of headaches and blurred vision (uncorrected visual acuity: 0.1 decimal) that showed on examination miotic pupils, pseudomyopia, no ocular motility restrictions, and no associated neurological disease. After initial treatment with cyclopentolate for two months, pseudomyopia persisted with an intermittent and variable esotropia. Spectacles of +1 both eyes and atropine 1% one drop daily were then prescribed. The situation improved and remained stable for several weeks, with pseudomyopia and esotropia reappearing later. Finally, botulinum toxin (2.5 iu Botox®) was injected in the medial rectus muscle on two occasions and a visual therapy program based on the stimulation of fusional divergence, diplopia, and stereopsis consciousness was recommended. This prescription was combined with the use of atropine during the first few weeks. Orthotropia and corrected distance visual acuity of 1.0 were found three months after treatment. The evolution and clinical results of this case report suggest that botulinum toxin in combination with other therapeutic alternatives may be useful in the treatment of spasm of the near reflex.

Maternal separation followed by isolation-housing differentially affects prepulse inhibition of the acoustic startle response in C57BL/6 mice

Exposure to chronic stress is associated with an increased incidence of neuropsychiatric dysfunction. The current study evaluated two competing hypotheses, the cumulative stress and the match/mismatch hypothesis of neuropsychiatric dysfunction, using two paradigms relating to exposure to “stress”: pre-weaning maternal separation and post-weaning isolation-housing. C57BL/6 offspring were reared under four conditions: typical animal facility rearing (AFR, control), early handling (EH, daily 15 min separation from dam), maternal separation (MS, daily 4 hr separation from dam), and maternal and peer separation (MPS, daily 4 hr separation from dam and from littermates). After weaning, mice were either housed socially (2–3/cage) or in isolation (1/cage) and then tested for prepulse inhibition in adulthood. Isolation-housed MPS subjects displayed greater deficits in prepulse inhibition relative to socially-housed MPS subjects while socially-housed AFR subjects displayed greater deficits in prepulse inhibition relative to isolation-housed AFR subjects. The results indicate that these treatment conditions represent a potentially valuable model for evaluating the match/mismatch hypothesis in regards to neuropsychiatric dysfunction.

Description of the reflex zenith tube of the Royal Observatory, Greenwich.

Forming Appendix I. to the Volume of Greenwich observations for the year 1854.

The muscular tension reflex and two of its modifying conditions

"References": p. [22]

Muscular contraction and the reflex control of movement,

"A chronological list of important contributions to the physiology of muscle": p. 53-55.

Combined prenatal and chronic postnatal vitamin D deficiency in rats impairs prepulse inhibition of acoustic startle

There is growing evidence that 1,25-dihydroxyvitamin D-3 is involved in normal brain development. The aim of this study was to examine the impact of prenatal and postnatal hypovitaminosis D on prepulse inhibition (PPI) of acoustic startle in adult rats. We compared six groups of rats: control rats with normal vitamin D throughout life and normal litter size (Litter); control rats with normal vitamin D but with a reduced litter size of two (Control); offspring from reduced litters of vitamin D deplete mothers who were repleted at birth (Birth), repleted at weaning (Weaning) or remained on a deplete diet until 10 weeks of age (Life); or control rats that were placed on a vitamin D-deficient diet from 5 to 10 weeks of age (Adult). All rats were tested in acoustic startle chambers at 5 and 10 weeks of age for acoustic startle responses and for PPI. There were no significant group differences at 5 weeks of age on the acoustic startle response or on PPI. At 10 weeks of age, rats in the Life group only had impaired PPI despite having normal acoustic startle responses. We conclude that combined prenatal and chronic postnatal hypovitaminosis D, but not early life hypovitaminosis D, alters PPI. (C) 2004 Elsevier Inc. All rights reserved.

Molecular structure and function of the glycine receptor chloride channel

The glycine receptor chloride channel (GlyR) is a member of the nicotinic acetylcholine receptor family of ligand-gated ion channels. Functional receptors of this family comprise five subunits and are important targets for neuroactive drugs. The GlyR is best known for mediating inhibitory neurotransmission in the spinal cord and brain stem, although recent evidence suggests it may also have other physiological roles, including excitatory neurotransmission in embryonic neurons. To date, four alpha-subunits (alpha1 to alpha4) and one beta-subunit have been identified. The differential expression of subunits underlies a diversity in GlyR pharmacology. A developmental switch from alpha2 to alpha1beta is completed by around postnatal day 20 in the rat. The beta-subunit is responsible for anchoring GlyRs to the subsynaptic cytoskeleton via the cytoplasmic protein gephyrin. The last few years have seen a surge in interest in these receptors. Consequently, a wealth of information has recently emerged concerning Glyl? molecular structure and function. Most of the information has been obtained from homomeric alpha1 GlyRs, with the roles of the other subunits receiving relatively little attention. Heritable mutations to human GlyR genes give rise to a rare neurological disorder, hyperekplexia (or startle disease). Similar syndromes also occur in other species. A rapidly growing list of compounds has been shown to exert potent modulatory effects on this receptor. Since GlyRs are involved in motor reflex circuits of the spinal cord and provide inhibitory synapses onto pain sensory neurons, these agents may provide lead compounds for the development of muscle relaxant and peripheral analgesic drugs.

Differentiation between protective reflexes: Cardiac defense and startle

Rise time and duration are two parametric characteristics of the eliciting stimulus frequently used to differentiate among psychophysiological reflexes. The present research varied the duration (study 1) and rise time (study 2) of an intense acoustic stimulus to dissociate cardiac defense and cardiac startle using the eyeblink response as the external criterion of startle. In each study, 100 participants were presented with five white noise stimuli of 105 dB under one of five duration (50, 100, 250, 500, and 1000 ms) or rise time (0, 24, 48, 96, and 240 ms) conditions. Cardiac defense was affected by stimulus duration, present only in the 500- and 1000-ms conditions, but not by stimulus rise time, present in all rise time conditions. Rise time affected blink startle, but did not selectively alter the short latency accelerative component of the heart rate response, thus questioning whether it reflects startle.

Covariation and interference between physiological reflexes: Eye-blink startle cardiac defense, and skin conductance

Comparative studies of autonomic and somatic reflexes, such as cardiac defense and motor startle, are rare. However, examination of the pattern of covariation, independence, or interference among physiological reflexes may help to clarify their functional significance and elucidate their complex modulation by psychological factors. Here we report the results of a study that examined the pattern of interference of eye-blink startle on subsequent cardiac defense. Participants were 63 students (31 women) distributed into three groups according to the sensory modality of the eliciting stimulus during the startle trials: acoustic high intensity (105 dB), acoustic low intensity (65 dB), and visual modality. Startle trials consisted of 12 presentations of the eliciting stimulus with a duration of 50 ms, instantaneous risetime, and a variable inter-stimulus interval of 16 – 20 s.Defense trials began 20 s after the last startle trial and consisted, for all groups, of 3 presentations of the high intensity acoustic stimulus with a duration of 500 ms and an inter-stimulus interval of 215 s. Results showed a clear interference of the startle trials on the subsequent defense trials when both types of trials shared identical sensory modality (acoustic) independently of intensity: the expected pattern of cardiac defense in the first trial only appeared in the visual modality. Similar interference effects were observed in the skin conductance response. Subjective reactivity to the defense stimulus did not detect differences between conditions.