Quantifying the Speed of Chromatophore Activity at the Single-Organ Level in Response to a Visual Startle Stimulus in Living, Intact Squid

The speed of adaptive body patterning in coleoid cephalopods is unmatched in the natural world. While the literature frequently reports their remarkable ability to change coloration significantly faster than other species, there is limited research on the temporal dynamics of rapid chromatophore coordination underlying body patterning in living, intact animals. In this exploratory pilot study, we aimed to measure chromatophore activity in response to a light flash stimulus in seven squid, Doryteuthis pealeii. We video-recorded the head/arms, mantle, and fin when squid were presented with a light flash startle stimulus. Individual chromatophores were detected and tracked over time using image analysis. We assessed baseline and response chromatophore surface area parameters before and after flash stimulation, respectively. Using change-point analysis, we identified 4,065 chromatophores from 185 trials with significant surface area changes elicited by the flash stimulus. We defined the temporal dynamics of chromatophore activity to flash stimulation as the latency, duration, and magnitude of surface area changes (expansion or retraction) following the flash presentation. Post stimulation, the response’s mean latency was at 50 ms (± 16.67 ms), for expansion and retraction, across all body regions. The response duration ranged from 217 ms (fin, retraction) to 384 ms (heads/arms, expansion). While chromatophore expansions had a mean surface area increase of 155.06%, the retractions only caused a mean reduction of 40.46%. Collectively, the methods and results described contribute to our understanding of how cephalopods can employ thousands of chromatophore organs in milliseconds to achieve rapid, dynamic body patterning.

Investigation of Visual Stimulus Signals Using Hue Change for SSVEP

This study focuses on the problem of eye irritation when measuring steady-state visual evoked potentials (SSVEPs) using a brain–computer interface and aims to clarify experimentally visual stimulus signals that do not cause discomfort to users. To this end, a method is proposed that introduces a flash stimulus in which the color is changed by changing its hue. This reduces the change in brightness while providing a color change, thereby facilitating visual stimulation with less discomfort. In experiments conducted, flash stimuli of the primary colors red, green, and blue and colors with different hues of 5–45° from these primary colors were generated to investigate the algorithm accuracy of SSVEP and discomfort. Subjective questionnaire and CFF values, which are ophthalmic parameters, were obtained for the subjects and compared to the discrimination rate. As a result of the comparison, it was confirmed that the fatigue level of the visual stimulus generated by the proposed hue change was lower than that of the conventional black-and-white stimulus. It was also confirmed that the combination of the hue difference and frequency could obtain the same discrimination rate as the conventional method.

Seizure triggered by flicker electroretinogram in a patient with no history of epilepsy

Purpose It is well known that repetitive flash stimulation may trigger seizures in susceptible individuals. Nevertheless, reports of such incidents occurring during recording of a flash electroretinogram (ERG) are extremely rare. Here, we describe the case of a photic-induced seizure triggered during an ERG recording in the absence of a history of epilepsy or other paroxysmal events. Methods A 14-year-old male patient presented with reduced visual acuity and impaired mesopic vision. Ophthalmological exams confirmed the patient’s complaints but were inconclusive as to the underlying pathophysiology. An ERG recording was performed, during which the 30-Hz flicker stimulus triggered a seizure. Results The ERG was essentially normal, with the exception of a 7-Hz rhythm superimposed onto the flicker ERG response that was recorded when the seizure developed. Conclusions The present case highlights the possibility that the 30-Hz ERG flash stimulus triggers a seizure in patients with no previous paroxysmal events. Literature evidence suggests that the likelihood of such an incident could be reduced by stimulating monocularly.

Dissociable saccadic suppression of pupillary and perceptual responses to light

We measured pupillary constrictions in response to full-screen flashes of variable luminance, occurring either at the onset of a saccadic eye movement or well before/after it. A large fraction of perisaccadic flashes were undetectable to the subjects, consistent with saccadic suppression of visual sensitivity. Likewise, pupillary responses to perisaccadic flashes were strongly suppressed. However, the two phenomena appear to be dissociable. Across subjects and luminance levels of the flash stimulus, there were cases in which conscious perception of the flash was completely depleted yet the pupillary response was clearly present, as well as cases in which the opposite occurred. On one hand, the fact that pupillary light responses are subject to saccadic suppression reinforces evidence that this is not a simple reflex but depends on the integration of retinal illumination with complex “extraretinal” cues. On the other hand, the relative independence of pupillary and perceptual responses suggests that suppression acts separately on these systems—consistent with the idea of multiple visual pathways that are differentially affected by saccades.

Fast Electrical Potential from a Long-Lived, Long-Wavelength Photoproduct of Fly Visual Pigment

A rapid electrical potential, which we have named the M-potential, can be obtained from the Drosophila eye using a high energy flash stimulus. The potential can be elicited from the normal fly, but it is especially prominent in the mutant norp AP12 (a phototransduction mutant), particularly if the eye color pigments are genetically removed from the eye. Several lines of evidence suggest that the M-potential arises from photoexcitation of long-lived metarhodopsin. Photoexcitation of rhodopsin does not produce a comparable potential. The spectral sensitivity of the M-potential peaks at about 575 nm. The M-potential pigment (metarhodopsin) can be shown to photoconvert back and forth with a "silent pigment(s)" absorbing maximally at about 485 nm. The silent pigment presumably is rhodopsin. These results support the recent spectrophotometric findings that dipteran metarhodopsin absorbs at much longer wavelengths than rhodopsin. The M-potential probably is related to the photoproduct component of the early receptor potential (ERP). Two major differences between the M-potential and the classical ERP are: (a) Drosophila rhodopsin does not produce a rapid photoresponse, and (b) an anesthetized or freshly sacrificed animal does not yield the M-potential. As in the case of the ERP, the M-potential appears to be a response associated with a particular state of the fly visual pigment. Therefore, it should be useful in in vivo investigations of the fly visual pigment, about which little is known.

Light-stimulated and light-inhibited bioluminescence of the euphausiid Meganyctiphanes norvegica (G. O. Sars)

Innocuous physiological stimuli which excite bioluminescence in Meganyctiphanes norvegica are few; one such is exposure to an appropriate light, another is chemical stimulation by 5-hydroxytryptamine. Meganyctiphanes responds to a photoflash, after some tens of seconds delay, with a bioluminescent glow lasting a few minutes. A second flash stimulus applied during this luminescent response rapidly abolishes it for tens of seconds, after which the glow returns again at full strength. Weak light of about the same colour and intensity as the animal’s own luminescence also depresses the flash-excited glow for the whole time the ambient light is present. 5-hydroxytryptamine (5- HT ), added to the sea water in which the animal swims can either excite continual luminescence or set whatever physiological controls exist into some hyper-sensitive state so that Meganyctiphanes becomes much more responsive to optical stimulation. The delay of onset, duration, amplitude and time course of flash-excited luminescence have been determined quantitatively, together with their dependence upon the intensity and spectral composition of the stimulating flash. Some characteristics of the inhibition by flash and by weak continuous light have been recorded, and also the interaction of 5- HT sensitization upon light excitation and inhibition. These optical stimulus-bioluminescent response relationships establish a well-documented excitatory stimulus which can be used to initiate luminescence at will, leaving the animal in its natural physio-chemical environment. The observations provide an experimental basis for judging some hitherto weakly based speculations about the physiological control of bioluminescence in Meganyctiphanes and suggest sensible ways to investigate this in greater detail.