The inhibition of the pupillary light reflex by the threat of an electric shock: a potential laboratory model of human anxiety

Abstract

It has been shown that the eye-blink response evoked by an abrupt loud white noise ('acoustic startle') is potentiated when the subjects anticipate an aversive stimulus, e.g. an electric shock ('fear-potentiated startle'). It has been proposed that this paradigm may be a useful laboratory model of human anxiety. We examined whether the threat of an electric shock, as used in the fear-potentiated startle paradigm, would affect the pupillary light reflex, in 12 healthy volunteers. Light stimuli (0.32 mW/cm(2), 200 msec) were generated by a light-emitting diode, and pupil diameter was monitored by computerized binocular infrared television pupillometry in the dark. The light reflex was recorded during either the anticipation of a shock ('threat' blocks) or periods in which no shocks were anticipated ('safe' blocks). The shock consisted of a single square wave current pulse (1.5 mA, 50 msec) applied to the median nerve. At the end of each 'threat' or 'safe' block, subjects rated their anxiety using visual analogue scales. Two-factor analysis of variance (condition x block) showed that in the 'threat' condition there was a consistent increase in initial pupil diameter, a decrease in light reflex amplitude and an increase in alertness and anxiety ratings. These effects were observable before the subjects received any shock (a single stimulation of the median nerve). These results show that the anticipation of an electric shock can modify not only the startle reflex response but also the pupillary light reflex, suggesting that the inhibition of the light reflex by threat may be another suitable laboratory model of human anxiety.

Effect of distracting faces on visual selective attention in the monkey

“…Pupil diameter may increase in proportion to mental effort (45), arousal (46), and attention (47). In humans, threat of shock reduced the pupillary light reflex (48), whereas diazepam antagonized the effect (48). Thus, the effect we observed may be due to a task-related expectancy of seeing threatening faces.…”

Relationship between sedation and pupillary function: comparison of diazepam and diphenhydramine

“…The method used here was similar to that used by Bitsios et al [6,18,27]. The sampling rate of the pupillometer was 50 Hz and the detection accuracy was better than 0.05 mm.…”

“…diameter of the pupil before the application of the light stimulus) and amplitude (i.e. the difference between the initial and the minimal diameters of a pupillary response to a light flash, mm) were measured [18,27,28].…”

“…diameter of the pupil before the application of the light stimulus) and amplitude (i.e. the difference between the initial and the minimal diameters of a pupillary response to a light flash, mm) were measured [18,27,28].Nonpupillary autonomic functions Blood pressure and heart rate recordings were taken in the sitting position using an electroaneroid sphygmomanometer.Skin conductance recordings were made via two 8-mm diameter silver-silver chloride surface electrodes taped to the terminal phalanges of the first two fingers of the left hand. Skin conductance was monitored via a CED 2502-SA interface connected to the same CED 1401 + computer that was used to control the light reflex stimuli.…”

Mechanisms underlying memory enhancement in humans

“…To specifically test this explanation, we examined a measure of arousal derived from pupillary measures recorded in Exp 6. The lightreflex (pupil constriction in response to light) shows reduced amplitude in patients with generalized anxiety (Bakes, Bradshaw, & Szabadi, 1990), and is reduced in healthy individuals in the context of arousal produced by pain expectation with the decrease of the light reflex response, but not the increase in the initial diameter of the pupil, correlating with increased subjective anxiety (Bitsios, Szabadi, & Bradshaw, 1996). We therefore calculated the light-reflex amplitude for all participants in Exp 6 by averaging across all trials during encoding for each subject.…”