Phasic Pupil Research Articles

Assessing Rod, Cone, and Melanopsin Contributions to Human Pupil Flicker Responses

We determined the relative contributions of rods, cones, and melanopsin to pupil responses in humans using temporal sinusoidal stimulation for light levels spanning the low mesopic to photopic range. A four-primary Ganzfeld photostimulator controlled flicker stimulations at seven light levels (-2.7 to 2 log cd/m(2)) and five frequencies (0.5-8 Hz). Pupil diameter was measured using a high-resolution eye tracker. Three kinds of sinusoidal photoreceptor modulations were generated using silent substitution: rod modulation, cone modulation, and combined rod and cone modulation in phase (experiment 1) or cone phase shifted (experiment 2) from a fixed rod phase. The melanopsin excitation was computed for each condition. A vector sum model was used to estimate the relative contribution of rods, cones, and melanopsin to the pupil response. From experiment 1, the pupil frequency response peaked at 1 Hz at two mesopic light levels for the three modulation conditions. Analyzing the rod-cone phase difference for the combined modulations (experiment 2) identified a V-shaped response amplitude with a minimum between 135° and 180°. The pupil response phases increased as cone modulation phase increased. The pupil amplitude increased with increasing light level for cone, and combined (in-phase rod and cone) modulation, but not for the rod modulation. These results demonstrate that cone- and rod-pathway contributions are more predominant than melanopsin contribution to the phasic pupil response. The combined rod, cone, and melanopsin inputs to the phasic state of the pupil light reflex follow linear summation.

Pupillometry and P3 index the locus coeruleus–noradrenergic arousal function in humans

The adaptive gain theory highlights the pivotal role of the locus coeruleus-noradrenergic (LC-NE) system in regulating task engagement. In humans, however, LC-NE functional dynamics remain largely unknown. We evaluated the utility of two candidate psychophysiological markers of LC-NE activity: the P3 event-related potential and pupil diameter. Electroencephalogram and pupillometry data were collected from 24 participants who performed a 37-min auditory oddball task. As predicted by the adaptive gain theory, prestimulus pupil diameter exhibited an inverted U-shaped relationship to P3 and task performance such that largest P3 amplitudes and optimal performance occurred at the same intermediate level of pupil diameter. Large phasic pupil dilations, by contrast, were elicited during periods of poor performance and were followed by reengagement in the task and increased P3 amplitudes. These results support recent proposals that pupil diameter and the P3 are sensitive to LC-NE mode.

Pupillometric evidence for a role of locus coeruleus in dynamic belief updating

Pupillometric evidence for a role of locus coeruleus in dynamic belief updating

Greater pupillary escape differentiates central from peripheral visual field loss

ObjectiveTo test whether pupil escape observed during a constant light stimulus was greater in eyes with central visual field loss compared to eyes with peripheral visual field loss and normal eyes. DesignComparative, observational case series. ParticipantsTwenty-seven normal subjects, 5 patients with central field loss, 11 patients with peripheral field loss, and 8 patients with combined loss (central and peripheral visual field loss) were tested. MethodsA dual-channel infrared pupillograph was used to simultaneously record the right and left pupil diameters at a rate of 60 Hz to characterize the initial, phasic pupil contraction, and the sustained, or prolonged, pupil contraction in response to a 5-second light stimulus. Full-field light stimuli with a diameter of 30° were presented to each eye at seven different intensities. Main outcome measuresThe amplitude of the phasic pupil contraction was compared with the amplitude of the sustained pupil contraction at the four brightest intensities (slope of phasic versus sustained contraction) in the normal eyes and in eyes with visual field loss in the center and the periphery. ResultsThe sustained pupillary contraction showed a statistically greater reduction in proportion to the phasic component in eyes with central field loss compared to those with peripheral field loss, combination central and peripheral field loss, and normal eyes. ConclusionsAfferent neurons from the central retina normally contribute a substantial component to the sustained pupil response. Eyes with central field loss can be distinguished from eyes with peripheral field loss by a relatively greater loss of the sustained response, causing greater pupil escape. This study showed that pupil movements in response to a nonperimetric full-field light stimulus may provide some degree of mapping of retinotopic sensitivity. This information may be of use in interpreting the pupillary movements during the swinging flashlight test and may help predict the pattern of visual field loss.

Phasic Pupil Dilation Response to Noxious Stimulation

Abstract The pupil dilation response (PDR) to a painful stimulus is a subtle, event-related increase in pupil diameter that occurs following brief noxious stimulation. It varies in amplitude with increasing stimulus intensity. Two competing hypotheses for the PDR are that (1) it reflects event-related cognitive efforts largely independent of pain, such as the task demand of discriminating intensity and readying a subjective report; and (2) like the pupillary light reflex, it is a simple reflexive response. In this study 21 subjects (11 male, 10 female) experienced painful stimuli matched in subjective intensity at two sites: finger tip and ear lobe, but they produced no subjective reports. If the PDR is a product of discriminating stimulus intensity levels and forming a report, then it should be minimal or nonexistent when subjects have no choices and make no overt judgments. On the other hand, if it is primarily a simple sympathetic reflex, then onset and peak latency should be longer for finger tip than for ear lobe stimulation because the conduction distance is longer. In addition to addressing these issues, we explored sex differences and the influence of age. Clear and similar PDRs appeared in response to stimulation of both sites despite an absence of subjective report requirements. PDR onset, peak amplitude and peak latency did not differ significantly across stimulation sites. Therefore, the PDR is neither an artifact of subjective report nor an uncomplicated sympathetic reflex. It appears to be an emotional arousal response, such as the defense response, the strength of which depends upon the magnitude of the noxious sensory input. Sex differences emerged, with women demonstrating a borderline larger PDR peak amplitude than men (P = .059) and a more rapid half recovery latency (P = .031). Age did not affect the PDR except at onset, with older subjects demonstrating a later onset latency (P = .003). The PDR may reflect preconscious processing associated with attention and perhaps other cognitive aspects of perception.

Phasic pupil dilation response to noxious stimulation in normal volunteers: Relationship to brain evoked potentials and pain report

Pupillary response to noxious stimulation was investigated in men (n = 11) and women (n = 9). Subjects experienced repeated trials of noxious electrical fingertip stimulation at four intensities, ranging from faint to barely tolerable pain. Measures included pupil dilation response (PDR), pain report (PR), and brain evoked potentials (EPs). The PDR began at 0.33 s and peaked at 1.25 s after the stimulus. Multivariate mixed-effects analyses revealed that (a) the PDR increased significantly in peak amplitude as stimulus intensity increased, (b) EP peaks at 150 and 250 ms differed significantly in both amplitude and latency across stimulus intensity, and (c) PR increased significantly with increasing stimulus intensity. Men demonstrated a significantly greater EP peak amplitude and peak latency at 150 ms than did women. With sex and stimulus intensity effects partialled out, the EP peak latency at 150 ms significantly predicted PR, and EP peak amplitude at 150 ms significantly predicted the PDR peak amplitude.