Modulatory Influence of Continuous Tone, Tone Offset, and Tone Onset on the Human Acoustic Startle Response

Startle modulation in young adult men, by continuous background tone and its offset, a 2-s sustained tone and its offset, and the onset of a 25-ms tone pip were compared. Tone (75dB 1000 Hz) offset and onset occurred either 2000 ms or 100-120 ms before the startle stimuli (104dB (SPL), 50-ms white noise bursts). Blink amplitude and latency were unaffected by continuous background tone. Blink amplitude was reliably inhibited by 100-ms offset of both the continuous background tone and the 2-s sustained tone or 120-ms onset of the tone pip, whereas effects on latency were more variable. Facilitation of blink amplitude and latency was significant but weak and only following the 2-s sustained tone, and only with respect to one of two experimental contexts. These findings support those of others and suggest that startle inhibition results from activation of neurons responding to transient environmental changes. The degree of inhibition appears to be related to stimulus value. Startle amplitude facilitation following long sustained prestimulation intervals is dependent on experimental context. Overall latency and amplitude modulation tend to be concordant, leading to the conclusion that the mechanism(s) underlying both are context dependent and linked in the adult human.     

The blink reflex and somatosensory evoked potential in optic neuritis in South India

Optic Neuritis (ON) proceeds to multiple sclerosis (MS) in a considerable number of patients. The blink reflex (BR) and somatosensory evoked potential (SSEP) are useful non-invasive tests that can detect silent lesions in the central nervous system in patients with clinically suspect MS. In the present study, the BR and SSEP were done in 20 healthy controls and 20 patients with ON. Abnormalities of the SSEP were seen in 20%, and of the BR in 30% of the patients with ON. On combining the results of SSEP and BR studies, 45% of the ON patients were seen to have abnormalities. Over a short period of follow-up, 2 of the 20 ON patients developed clinical MS and both of them had had abnormalities of the BR. These findings suggest that ON proceeding to MS in India may be more common than suspected at present.     

Glabella tap sign: Is it due to a lack of R2-habituation?

In 30 patients with Parkinson's disease, 55 patients with other neurological disorders and 25 normal subjects, both upper eyelid movements and orbicularis oculi reflexes to repetitive glabella taps were simultaneously recorded using a newly devised apparatus for the measurement of eyelid movement. Upper lid movement during the blink reflex has been thought to correspond to the late component of the two components of the orbicularis oculi reflex, and failure of habituation of the late component to repetitive stimuli has been considered to be responsible for the glabella tap sign. However, the present study showed that the eyelid lowered after the early component (R1), and habituation of the late component (R2) was recognized in 31% of subjects with the glabella tap sign. This shows that there is no direct causual relationship between the glabella tap sign and lack of the habituation of the late component.     

Lack of visual suppression in the rabbit lateral geniculate nucleus during blink reflex

Stimulation of the supraorbital branch of the trigeminal nerve (SO) elicited eye blinks in the rabbit, but did not decrease the amplitude of visual cortical evoked potential from stimulation of the optic chiasm (OX). In addition, the SO stimulation neither induced an inhibitory postsynaptic potential (IPSP) in LGN cells, nor activated inhibitory interneurons in the thalamic reticular nucleus (TRN), which proved to mediate both recurrent inhibition and saccadic suppression in the dorsal lateral geniculate nucleus (LGN). All these indicate that there is no visual suppression in the rabbit LGN during blink reflex.     

Reflexes and the eye

Reflexes are an essential part of protective and homeostatic function, both in general terms and with specific reference to ocular structures. A wide range of stimuli and responses, with varying degrees of central processing, is involved in such reflexes. The simplest reflexes are monosynaptic, such as the stretch or myotatic reflex. More complex polysynaptic reflexes are involved in many regulatory and protective functions - these include autonomic as well as somatic reflexes. Ocular autonomic reflexes include the oculocardiac, pupillary, accommodative and lacrimatory reflexes. Ocular somatic reflexes include eyelid and extra-ocular muscle reflexes (such as Bell's phenomenon, vestibulo-ocular and optokinetic reflexes). An account of the above reflexes is given in the format of an essay, modified from the FRACO Part I Examination in Physiology. The topic was ‘Discuss reflex activities with particular reference to the eye’. The content is based on several of the texts recommended for the Part I Examination, as listed under references.     

The blink reflex in chronic tension-type headache, migraine, and cervicogenic headache

R1 and R2 blink reflex latencies were investigated blind in 10 patients with cervicogenic headache, 11 patients with chronic tension-type headache, 11 patients with migraine, and 9 headache-free controls. There were no R1 or R2 latency differences between the four groups. The latency of R1 increased significantly with headache duration in tension-type headache patients. Shorter R1 latencies were found on the symptomatic side than on the non-symptomatic side in cervicogenic headache patients. The results suggest that a state of hyperactivity may be present in the ipsilateral trigeminal nucleus in cervicogenic headache. Hypoactivity, however, may develop over time in tension-type headache.     

Development of multimodal attention in young infants: modification of the startle reflex by attention

This study examined the effect of attention engagement to compound auditory-visual stimuli on the modification of the startle blink reflex in infants. Infants at 8, 14, 20, or 26 weeks of age were presented with interesting audiovisual stimuli. After stimulus onset, at delays defined by heart rate changes known to be associated with sustained attention or attention disengagement, blink reflexes were elicited by visual or auditory stimuli. Blink amplitude to either visual or auditory stimuli was enhanced when the infants were engaged in attention to the foreground auditory-visual stimuli relative to control trials with no foreground patterns. This enhancement of the blink amplitude increased from 8 to 26 weeks of age. In contrast to selective modality enhancement for single-modality foreground stimuli, these results show that these multimodal stimuli engage both visual and auditory attention systems in this age range.     

Attentional blink reflex modulation in a continuous performance task is modality specific

Four experiments investigated the attentional modulation of acoustic blinks during continuous spatial tracking tasks. Experiment 1 found blink magnitude inhibition in a visual tracking task. Experiment 2 replicated this finding and also found blink latency slowing. Experiment 3 varied the difficulty of the task and found larger blink inhibition in the easy condition. Blink latency slowing did not differ and was significant at both difficulty levels. Experiment 4 employed less difficult visual and acoustic tracking tasks at two levels of task load. Blink magnitude inhibition during the visual and facilitation during the acoustic task was significant during high load in both modality groups. Blink latency was slowed in all visual task conditions and shortened in the difficult acoustic task. These results indicate that attentional blink modulation in a continuous spatial tracking task is modality specific.     

The effect of stimulus modality and task difficulty on attentional modulation of blink startle

The effects of the sensory modality of the lead stimulus and of task difficulty on attentional modulation of the electrical and acoustic blink reflex were examined. Participants performed a discrimination and counting task with either two acoustic, two visual, or two tactile lead stimuli. In Experiment 1, facilitation of the electrically elicited blink was greater during task-relevant than during task-irrelevant lead stimuli. Increasing task difficulty enhanced magnitude facilitation for acoustic lead stimuli. In Experiment 2, acoustic blink facilitation was greater during task-relevant lead stimuli, but was unaffected by task difficulty. Experiment 3 showed that a further increase in task difficulty did not affect acoustic blink facilitation during visual lead stimuli. The observation that blink reflexes are facilitated by attention in the present task domain is consistent across a range of stimulus modality and task difficulty conditions.     

Quantitative videographic analysis of blink patterns of newscasters

BACKGROUND: To determine the blink patterns of newscasters. METHODS: The blink patterns of 39 professional newscasters (24 Japanese and 19 non-Japanese, 19 men and 20 women, mean age: 34.5 +/- 6.5 years) were analyzed by a blink analyzer in this observational case series. Sixty-four normal Japanese volunteers (35 men and 29 women, mean age: 31.2 +/- 7.6 years) were used as lay normal controls. RESULTS: The maximum, mean, and coefficient of variation (CV) of interblinking time (IBT: the time between one blink and the next) in newscasters were 2.36 +/- 0.90 s (P < 0.0005), 0.95 +/- 0.27 s (P < 0.0005), and 0.76 +/- 0.25 (P < 0.0005), respectively, while those of the controls were 8.87 +/- 3.96 s, 4.01 +/- 2.05 s, and 0.55 +/- 0.21, respectively. The maximum, mean, and CV of the blinking time (BT: the length of time for each blink) of newscasters were 0.71 +/- 0.43 s (P < 0.0005), 0.29 +/- 0.11 s (P < 0.0005), and 0.55 +/- 0.25 (P < 0.0005), respectively. The values were longer when compared with normal controls, which were also significantly different, 0.35 +/- 0.12 s, 0.20 +/- 0.04 s and 0.23 +/- 0.09, respectively. CONCLUSIONS: The six blink-related factors varied between newscasters and normal controls. Newscasters blink more often with greater irregularity.