After images from Memantine

After images under the influence of psychoactive substances are dramatically intensified versions of the normal physiological phenomenon where retinal cells continue to fire after stimulation ceases. From a first-person perspective, glancing at a bright object — a lamp, a window, a person's face — and then looking away reveals a vivid, lingering copy of that image burned into the visual field. Unlike sober afterimages, which are typically faint and rapidly fading, substance-enhanced afterimages can be remarkably detailed, maintaining clear color information, sharp edges, and recognizable form. They overlay whatever one is currently viewing, creating a layered visual experience where the present scene is stamped with ghostly impressions of moments just past.

The intensity of after images scales with both substance dose and the brightness of the stimulus. At mild levels, they manifest as slightly more persistent versions of normal afterimages — looking away from a light source leaves a lingering spot that takes longer than usual to fade. At moderate levels, afterimages become unmistakably enhanced, retaining color and detail for several seconds and appearing with minimal stimulation. At high levels, nearly every visual fixation leaves a persistent trace, creating a cumulative layering effect where the visual field becomes populated with overlapping ghostly impressions of recent visual experiences.

After images present in several characteristic variations. "Positive afterimages" retain the original colors and luminance of the stimulus, appearing as transparent copies overlaid on current vision. "Negative afterimages" display complementary colors — a red object leaves a green impression. "Palinopsia" is a related phenomenon where entire visual scenes persist and repeat, creating a more complex and extended version of simple afterimages. "Trailing afterimages" connect to the tracers effect, where moving objects leave a continuous stream of afterimage copies rather than a single static imprint.

The mechanism involves both retinal and cortical processes. At the retinal level, photoreceptor cells become temporarily saturated by intense light exposure, continuing to signal after the stimulus is removed. Psychoactive substances — particularly serotonergic psychedelics — appear to amplify this process by increasing neural excitability throughout the visual processing pathway. At the cortical level, 5-HT2A receptor activation in the visual cortex appears to reduce the brain's normal suppression of residual visual signals, allowing afterimages that would normally be filtered out of conscious awareness to persist and intensify.

After images are commonly enhanced by classical psychedelics including LSD, psilocybin, mescaline, and the 2C-x family. They are particularly prominent with LSD, where they often combine with tracers to create complex trailing visual effects. MDMA produces mild afterimage enhancement in some users. Cannabis can enhance afterimage persistence, particularly at higher doses. Certain dissociatives may also produce afterimage-like phenomena. The effect is often among the first visual changes noticed during a psychedelic come-up and among the last to fade during the come-down.

After images are generally a benign and often aesthetically interesting visual effect. The primary concern is that intense afterimage persistence can become disorienting, particularly in environments with high visual contrast or rapidly changing light conditions. In rare cases, persistent afterimage-like phenomena can continue beyond the acute drug experience, a condition known as Hallucinogen Persisting Perception Disorder (HPPD). While typically mild, HPPD can be distressing and persistent. Risk factors for HPPD include frequent psychedelic use, high doses, and concurrent cannabis use. Most instances resolve spontaneously over weeks to months.