Mirror writing is formed by writing in the direction that is the reverse of the natural way for a given language, such that the result is the mirror image of normal writing: it appears normal when it is reflected in a mirror. It is sometimes used as an extremely primitive form of cipher. The most common modern usage of mirror writing can be found on the front of ambulances, where the word "AMBULANCE" is often written in very large mirrored text, so that drivers see the word the right way around in their rear-view mirror.
Research suggests that the ability to do mirror writing[clarification needed] is probably inherited and caused by atypical language organization in the brain. It is not known how many people in the population inherit the ability of mirror writing (an informal Australian newspaper experiment identified 10 true mirror-writers in a readership of 65,000). Half of the children of people with the ability inherit it. There are more left-handed mirror writers than right-handed ones, probably because left-handed people tend to have atypical language centers in their brain. 15% of left-handed people have the language centres in both halves of their brain. The cerebral cortex (thin layer of dense brain cells covering the whole brain) and motor homunculus (relates to voluntary movement) are affected by this causing them to be able to read and write backwards quite naturally.
In an experiment conducted by the Department of Neurosurgery at Hokkaido University School of Medicine in Sapporo, Japan, Scientists proposed that the origin of mirror writing comes from damage caused through accidental brain damage or neurological diseases, such as an essential tremor, Parkinson’s disease, or spino-cerebellar degeneration. This hypothesis was proposed due to the fact that these conditions affect a “neural mechanism that controls the higher cerebral function of writing via the thalamus.”  Another study by the same university discovered that damage was not the only cause. The scientists observed that normal children exhibited signs of mirror writing while learning to write, thus concluding that currently there is no exact method for finding the true origin of mirror writing.
- Mathewson I. (2004). "Mirror writing ability is genetic and probably transmitted as a sex-linked dominant trait: it is hypothesised that mirror writers have bilateral language centres with a callosal interconnection". Med Hypotheses. 62 (5): 733–9. doi:10.1016/j.mehy.2003.12.039. PMID 15082098.
- News in Science - Mirror writing: my genes made me do it - 02/06/2004
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- This browser app for the iPhone/iPad displays websites with left/right mirroring, and is thus well-suited for practicing to read mirror writing
- Mirror Writing a genetic trait
- Jay A. Gottfried, Feyza Sancar, Anjan chatterjee. "Acquired mirror writing and reading: evidence for reflected graphemic representations".