Alice in Wonderland
When Lewis Carroll first described Alice’s experiences of being too large or too small for a room, nobody knew that he himself had been experiencing these same delusions. All the while, Lewis Carroll (the pseudonym for Charles L. Dodgson) was experiencing migraine headaches which manifested with very unusual visual disturbances. In this week’s episode of BrainWaves we discuss how structural injury to the brain can result in the distortions of visual perception experienced by Dodgson and many many others.
It’s worth starting with the basic process of higher order visual processing, which Dr. Aguirre presented in his earlier episode on Agnosia. Here’s that link in case you missed it:
Once you’ve mastered these concepts, it gets easier to understand the neural circuitry that underlies a disturbed visual scene.
Beginning with a lesion of the bilateral occipital poles, V1 (primary visual cortex), the patient will not be able to register any conscious visual input that originated in the retina. They are cortically blind (much less common than retinal blindness), a disorder called Anton’s syndrome.
Moving onto the “what” pathway, which is responsible for processing and recognition of object information–like identifying a pair of scissors as a pair of scissors, or a face as someone’s face–complex visual features of an object are integrated into a whole that is greater than the sum of its parts. So you can imagine that damage to this pathway can result in very specific deficits. For example, in damaging the right-sided posterior temporal lobe area, the face fusiform gyrus, the patient will retain the ability to perceive the face, the gender of that face, the facial expressions, the eyes, the nose, the mouth, and so on. But the patient with the damaged face fusiform gyrus won’t be able to assemble all that information into a useful concept of, “That’s a face I recognize.” You won’t know the person. Hearing their voice, however, will reveal the persona behind the person. That function remains intact.
But we don’t really emphasize these circuits in today’s episode. We talk a lot more about the interesting examples of visual system disturbances, which I’ll summarize here in no particular order. This list is by no means comprehensive,
and we cover several others in the episode:
- Charles Bonnet Syndrome: Starting most anteriorly in the nervous system, disease of the retina can impair the perception of light. Without appropriate input, obviously processing and interpretation will be limited. So what happens, in some cases of retinal disease (e.g., age-related macular degeneration), the mind will conjure a visual scene given the limited retinal input. For example, a poorly perceived shadow in the distance may be mistaken for a hooded man or a burglar.
- Anton Syndrome: Now, posteriorly in the occipital lobe, damage to primary visual cortex (V1) will result in a complete lack of early visual processing. The downstream processing mechanisms remain fully intact, so these neurons will continue to fire–albeit in an aberrant fashion. Therefore, as we frequently see in bilateral posterior cerebral artery infarctions, the patient will experience “cortical blindness” and believe they can see, but when confronted with visual stimuli, they will be clueless. This can be distinguished from a retinal blindness (more common) by testing for pupillary response. Reaction to light will remain normal in Anton Syndrome.
- Riddoch Syndrome: For reasons that are not completely clear, there have been cases in which a patient has damaged part of the left anterior occipital lobe, resulting in a right-sided homonymous hemianopsia. This is not surprising. What is surprising, however, is that some patients will have the preserved ability to detect motion in the area they cannot see. The most popular hypothesis for the Riddoch phenomenon is that these patients will access a subcortical pathway that uses the superior colliculi and dorsal midbrain which may be more attentive to motion.
- Palinopsia: By definition, palinopsia indicates visual perseveration, a.k.a. the perception of a persistent image as it moves across your visual field. As you already know, I am a huge fan of The Matrix. And one scene very nicely illustrates what a patient with palinopsia might see. Structurally, in the brain, patients with palinopsia may have a defect somewhere in the dorsal stream, in the where or how pathways where position and movement information is processed.
- Alice-in-Wonderland Syndrome: A.k.a., micropsia, macropsia, teleopsia, etc. As it turns out, the original patient with the Alice in Wonderland Syndrome also experienced these symptoms along with migrainous headaches. No, it wasn’t Alice. It was Alice’s creator, Lewis Carroll—or more accurately Charles L. Dodgson who assumed Lewis Carroll as his nom de plume. Dodgson’s portrayal of Alice in 1865 was very much autobiographical. Whereas Alice would experience her body shrink in size with ingestion of a magical tonic, or grow to several sizes larger after eating a cake, Dodgson documented subjective visual disturbances much like these in his personal diary. It would be nearly 100 years before physicians like Lippman and Todd would describe these visual perceptions in greater detail, as they accompany migraines. And at this time the title Alice-in-Wonderland Syndrome was born.
I’ll be the first to admit that the episode today was not comprehensive on this topic. I wish we could have had more time to talk about other causes of visual disturbances, like migraine and seizure, especially intoxication or withdrawal, and psychiatric disease. And while today’s episode featured all the interesting disturbances described as a kind of gain of function, localizing a lesion in the visual pathway probably has greater clinical value. At some point, we’ll talk more about that, but until then I’d recommend you grab a copy of the Neuro-ophthalmology textbook by Liu, Volpe, and Galetta. If you use this link, you can get a 15% discount:
Until next time, I’ll be seeing you…
BrainWaves podcasts and online content are intended for medical education only and should not be used to guide medical decision making in routine clinical practice. But if you are experiencing palinopsia palinopsia you should schedule an appointment to see your doctor doctor.
- Barton JJ. Disorders of higher visual processing. Handbook of clinical neurology. 2011;102:223-61.
- Meadows JC and Munro SS. Palinopsia. Journal of neurology, neurosurgery, and psychiatry. 1977;40:5-8.
- Radoeva PD, Prasad S, Brainard DH and Aguirre GK. Neural activity within area V1 reflects unconscious visual performance in a case of blindsight. J Cogn Neurosci. 2008;20:1927-39.
- Podoll K and Robinson D. Lewis Carroll’s migraine experiences. Lancet. 1999;353:1366.