Taste color and see sounds? Synesthesia may have a genetic basis.

Learning about synesthesia can help us better understand how our brain works, particularly in terms of perception.

Shutterstock/Big Think
Shutterstock/Big Think

Synesthesia is a condition where two of a person’s senses are intermingled. Either their cognitive or sensory pathways have some sort of overlap. It’s rare, affecting only 4-5% of the population, or about 1 in 2,000 people. Some experts however, believe about every 1 in 300 have some sort of variation of it, as there’s a wide variety of experiences one may place under the umbrella of synesthesia.


One person can say smell colors, while another tastes words, and another still visualizes sounds. For instance, linguistics professor Sean Day, PhD, at National Central University in Taiwan, told the APA’s Monitor on Psychology that "The taste of beef, such as a steak, produces a rich blue. Mango sherbet appears as a wall of lime green with thin wavy strips of cherry red. Steamed gingered squid produces a large glob of bright orange foam, about four feet away, directly in front of me."

To date, there are 60 recorded varieties of synesthesia, a word that in Greek means "to perceive together." But not all kinds deal with sensory perception. There’s also "conceptual synesthesia," where the person can easily visualize abstract concepts, usually mathematical ones. These are experienced as projections which appear either inside one’s mind or outside, somewhere in the environment. There are also many who experience more than one type of synesthesia.

Grapheme-color synesthesia is the most common variety. Here, each letter of the alphabet or number corresponds to a particular shade or color. Autistic savant Daniel Tammet is one such synesthete. He’s a mathematical and linguistic genius whose ability helps him to organize and manipulate numbers and letters in startling and innovative ways.

He can do astronomical calculations in his head and has memorized Pi up to 22,500 places. So far, Tammet’s learned 11 languages, including one he’s created himself. The savant once learned an entire language in one week, in order to impress a TV show host who was interviewing him at the end of it. To Tammet, every single number has a particular shape, color, and texture, which helps him organize thoughts in a unique way. A few famous synesthetes include author Vladimir Nabokov and musicians Billy Joel, Duke Ellington, and Lorde.

Daniel Tammet is an autistic savant and synesthete who can calculate Pi up to 22,500 places in his head. Credit: Getty Images.

Surprisingly, there seems to be tremendous consensus among those with synesthesia. The number five often appears red, for instance. Tuesday is the color orange. And among those with chromesthesia—where sight and sound combine, a C-sharp gives off a particular shade of blue.

Investigations into this bizarre and fascinating phenomenon has gone in and out of fashion since the late 19th century. What’s unfortunate is we have yet to understand the molecular basis for it. These days, scientists believe that by gaining more knowledge of the condition and how it works, we can develop a far deeper understanding of how our brain works, particularly in terms of perception. FMRI and positron-emission tomography scans of the brain, show that those with synesthesia have more activity in the sensory areas inside the cerebral cortex.

These scans also show unusual differences in brain structure and neural connectivity. As a result of this and the fact that the condition is more common among savants and those with autism, neuroscientists today believe that synesthesia is the result of unusual wiring in the brain that takes place during development. Synesthetes brains are likely hyperconnected.

A new study out of at the Max Planck Institute for Psycholinguistics in the Netherlands, has discovered genetic variants associated with synesthesia. Their findings were published in the journal Proceedings of the National Academy of Sciences (PNAS). Amanda Tilot was the lead researcher.

Sound–color synesthesia in three multiplex families from the Cambridge Synesthesia Research Group. (A) The families. Circles indicate females, squares males, and gray shading indicates synesthesia. (B) An illustration of sound–color matching over three trials (colored boxes) for three hypothetical individuals presented with two auditory stimuli. A synesthete (boxes on the left) would be highly consistent in all the trials, while someone who doesn’t have it (boxes on the right) would be inconsistent in their choices. Credit: PNAS.

“We demonstrate that three families who experience color when listening to sounds are connected by rare genetic variants affecting genes that contribute to axonogenesis, a process essential for neuronal connections within and across brain regions,” Tilot and colleagues write. “Our results connect synesthetes’ altered structural and functional connectivity to genes that support the development of those connections.”

While previous research had looked for the location of the condition within the brain, these researchers were the first to study synesthetes and their families’ genes. “We applied whole-exome sequencing to three families with sound–color (auditory–visual) synesthesia affecting multiple relatives across three or more generations,” researchers wrote. The families were purposely selected as they each had multiple members with the condition.

The geneticists compared and contrasted the genomes of family members who were synesthetes to those who weren’t. As a result, they identified 37 genes of interest. Six in particular were highlighted by the scientists: COL4A1, ITGA2, MYO10, ROBO3, SLC9A6, and SLIT2. These are known to be associated with axonogenesis and first become expressed during early childhood, which is also when synesthesia generally appears. This supports the hypothesis that synesthesia is the result of hyperconnectivity or having more neuronal connections inside the brain.

Getting a better grasp on merged senses can allow us to gain a deeper understanding of how the brain works. Credit: Getty Images.

Axonogenesis is when the axons grow and connect new synapses in order to deliver more information across the organ. According to this research, those with synesthesia may produce more connections than those with more typical sense experiences. Their neural connections may also reach areas farther afield.

This was a small sample size, however. More research by Tilot and colleagues is planned, including a wider pool of families with members who are known synesthetes. This time, they’re also including people with the condition who have no known family members with it. This particular follow-up study will also look at just one type, chromesthesia. But in the future, researchers plan to look into other forms of the synesthesia well.

To learn more about this condition, click here.

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7 most notorious and excessive Roman Emperors

These Roman Emperors were infamous for their debauchery and cruelty.

Nero's Torches. A group of early Christian martyrs about to be burned alive during the reign of emperor Nero in 64 AD.

1876. Painted by Henryk Siemiradzki.
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  • Roman Emperors were known for their excesses and violent behavior.
  • From Caligula to Elagabalus, the emperors exercised total power in the service of their often-strange desires.
  • Most of these emperors met violent ends themselves.

We rightfully complain about many of our politicians and leaders today, but historically speaking, humanity has seen much worse. Arguably no set of rulers has been as debauched, ingenious in their cruelty, and prone to excess as the Roman Emperors.

While this list is certainly not exhaustive, here are seven Roman rulers who were perhaps the worst of the worst in what was one of the largest empires that ever existed, lasting for over a thousand years.

1. Caligula

Officially known as Gaius (Gaius Caesar Augustus Germanicus), Caligula was the third Roman Emperor, ruling from 37 to 41 AD. He acquired the nickname "Caligula" (meaning "little [soldier's] boot") from his father's soldiers during a campaign.

While recognized for some positive measures in the early days of his rule, he became famous throughout the ages as an absolutely insane emperor, who killed anyone when it pleased him, spent exorbitantly, was obsessed with perverse sex, and proclaimed himself to be a living god.

Caligula gives his horse Incitatus a drink during a banquet. Credit: An engraving by Persichini from a drawing by Pinelli, from "The History of the Roman Emperors" from Augustus to Constantine, by Jean Baptiste Louis Crevier. 1836.

Among his litany of misdeeds, according to the accounts of Caligula's contemporaries Philo of Alexandria and Seneca the Younger, he slept with whomever he wanted, brazenly taking other men's wives (even on their wedding nights) and publicly talking about it.

He also had an insatiable blood thirst, killing for mere amusement. Once, as reports historian Suetonius, when the bridge across the sea at Puteoli was being blessed, he had a number of spectators who were there to inspect it thrown off into the water. When some tried to cling to the ships' rudders, Caligula had them dislodged with hooks and oars so they would drown. On another occasion, he got so bored that he had his guards throw a whole section of the audience into the arena during the intermission so they would be eaten by wild beasts. He also allegedly executed two consuls who forgot his birthday.

Suetonius relayed further atrocities of the mad emperor's character, writing that Caligula "frequently had trials by torture held in his presence while he was eating or otherwise enjoying himself; and kept an expert headsman in readiness to decapitate the prisoners brought in from gaol." One particular form of torture associated with Caligula involved having people sawed in half.

He caused mass starvation and purposefully wasted money and resources, like making his troops stage fake battles just for theater. If that wasn't enough, he turned his palace into a brothel and was accused of incest with his sisters, Agrippina the Younger, Drusilla, and Livilla, whom he also prostituted to other men. Perhaps most famously, he was planning to appoint his favorite horse Incitatus a consul and went as far as making the horse into a priest.

In early 41 AD, Caligula was assassinated by a conspiracy of Praetorian Guard officers, senators, and other members of the court.

2. Nero

Fully named Nero Claudius Caesar, Nero ruled from 54 to 68 AD and was arguably an even worse madman than his uncle Caligula. He had his step-brother Britannicus killed, his wife Octavia executed, and his mother Agrippina stabbed and murdered. He personally kicked to death his lover Poppeaea while she was pregnant with his child — a horrific action the Roman historian Tacitus depicted as "a casual outburst of rage."

He spent exorbitantly and built a 100-foot-tall bronze statue of himself called the Colossus Neronis.

He is also remembered for being strangely obsessed with music. He sang and played the lyre, although it's not likely he really fiddled as Rome burned in what is a popular myth about this crazed tyrant. As misplaced retribution for the fire which burned down a sizable portion of Rome in the year 64, he executed scores of early Christians, some of them outfitted in animal skins and brutalized by dogs, with others burned at the stake.

He died by suicide.

Roman Emperor Nero in the burning ruins of Rome. July 64 AD.Credit: From an original painting by S.J. Ferris. (Photo by Kean Collection / Getty Images)

3. Commodus

Like some of his counterparts, Commodus (a.k.a. Lucius Aelius Aurelius Commodus) thought he was a god — in his case, a reincarnation of the Greek demigod Hercules. Ruling from 176 to 192 AD, he was also known for his debauched ways and strange stunts that seemed designed to affirm his divine status. Numerous statues around the empire showed him as Hercules, a warrior who fought both men and beasts. He fought hundreds of exotic animals in an arena like a gladiator, confusing and terrifying his subjects. Once, he killed 100 lions in a single day.

Emperor Commodus (Joaquin Phoenix) questions the loyalty of his sister Lucilla (Connie Nielsen) In Dreamworks Pictures' and Universal Pictures' Oscar-winning drama "Gladiator," directed by Ridley Scott.Credit: Photo By Getty Images

The burning desire to kill living creatures as a gladiator for the New Year's Day celebrations in 193 AD brought about his demise. After Commodus shot hundreds of animals with arrows and javelins every morning as part of the Plebeian Games leading up to New Year's, his fitness coach (aptly named Narcissus), choked the emperor to death in his bath.

4. Elagabalus

Officially named Marcus Aurelius Antoninus II, Elagabalus's nickname comes from his priesthood in the cult of the Syrian god Elagabal. Ruling as emperor from 218 to 222 AD, he was so devoted to the cult, which he tried to spread in Rome, that he had himself circumcised to prove his dedication. He further offended the religious sensitivities of his compatriots by essentially replacing the main Roman god Jupiter with Elagabal as the chief deity. In another nod to his convictions, he installed on Palatine Hill a cone-like fetish made of black stone as a symbol of the Syrian sun god Sol Invictus Elagabalus.

His sexual proclivities were also not well received at the time. He was likely transgender (wearing makeup and wigs), had five marriages, and was quite open about his male lovers. According to the Roman historian (and the emperor's contemporary) Cassius Dio, Elagabalus prostituted himself in brothels and taverns and was one of the first historical figures on record to be looking for sex reassignment surgery.

He was eventually murdered in 222 in an assassination plot engineered by his own grandmother Julia Maesa.

5. Vitellius

Emperor for just eight months, from April 19th to December 20th of the year 69 AD, Vitellius made some key administrative contributions to the empire but is ultimately remembered as a cruel glutton. He was described by Suetonius as overly fond of eating and drinking, to the point where he would eat at banquets four times a day while sending out the Roman navy to get him rare foods. He also had little social grace, inviting himself over to the houses of different noblemen to eat at their banquets, too.

Vitellius dragged through the streets of Rome.Credit: Georges Rochegrosse. 1883.

He was also quite vicious and reportedly either had his own mother starved to death or approved a poison with which she committed suicide.

Vitellius was ultimately murdered in brutal fashion by supporters of the rival emperor Vespasian, who dragged him through Rome's streets, then likely beheaded him and threw his body into the Tiber river. "Yet I was once your emperor," were supposedly his last words, wrote historian Cassius Dio.

6. Caracalla

Marcus Aurelius Antoninus I ruled Rome from 211 to 217 AD on his own (while previously co-ruling with his father Septimius Severus from 198). "Caracalla"' was his nickname, referencing a hooded coat from Gaul that he brought into Roman fashion.

He started off his rise to individual power by murdering his younger brother Geta, who was named co-heir by their father. Caracalla's bloodthirsty tyranny didn't stop there. He wiped out Geta's supporters and was known to execute any opponents to his or Roman rule. For instance, he slaughtered up to 20,000 citizens of Alexandria after a local theatrical satire dared to mock him.

Geta Dying in His Mother's Arms.Credit: Jacques Pajou (1766-1828)

One of the positive outcomes of his rule was the Edict of Caracalla, which gave Roman citizenship to all free men in the empire. He was also known for building gigantic baths.

Like others on this list, Caracalla met a brutal end, being assassinated by army officers, including the Praetorian prefect Opellius Macrinus, who installed himself as the next emperor.

7. Tiberius

As the second emperor, Tiberius (ruling from 42 BC to 16 AD) is known for a number of accomplishments, especially his military exploits. He was one of the Roman Empire's most successful generals, conquering Pannonia, Dalmatia, Raetia, and parts of Germania.

He was also remembered by his contemporaries as a rather sullen, perverse, and angry man. In the chapter on his life from The Lives of the Twelve Caesars by the historian Suetonius, Tiberius is said to have been disliked from an early age for his personality by even his family. Suetonius wrote that his mother Antonia often called him "an abortion of a man, that had been only begun, but never finished, by nature."

"Orgy of the Times of Tiberius on Capri".Painting by Henryk Siemiradzki. 1881.

Suetonius also paints a damning picture of Tiberius after he retreated from public life to the island of Capri. His years on the island would put Jeffrey Epstein to shame. A horrendous pedophile, Tiberius had a reputation for "depravities that one can hardly bear to tell or be told, let alone believe," Suetonius wrote, describing how "in Capri's woods and groves he arranged a number of nooks of venery where boys and girls got up as Pans and nymphs solicited outside bowers and grottoes: people openly called this 'the old goat's garden,' punning on the island's name."

There's much, much more — far too salacious and, frankly, disgusting to repeat here. For the intrepid or morbidly curious reader, here's a link for more information.

After he died, Tiberius was fittingly succeeded in emperorship by his grandnephew and adopted grandson Caligula.

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