in beersheba, israel, in september 2021. bernado and arthur lima, three-year-old twins from roraima, brazil, were separated by a team led by owase jeelani in a rio de janeiro hospital. seven surgeries were needed, the last of which alone took 27 hours. the operation was particularly notable in that jeelani received assistance from great ormond street hospital in london via the use of virtual reality, as well as the twins being the oldest craniopagus twins to be separated. tatiana and krista lateral surface of cerebral cortex throughout history, the fascination about craniopagus twins has continually increased as neurobiology and the field of neuroscience has become more interesting to the public. in 2011, the new york times magazine covered a story of two craniopagus twin girls who share a brain and seem to show all different kinds of physiological and emotional responses due to their condition. though krista and tatiana hogan share a brain, the two girls showed distinct personalities and behavior. one example was when krista started drinking her juice tatiana felt it physically going through her body. in any other set of twins the natural conclusion about the two events would be that krista's drinking and tatiana's reaction would be coincidental. but because krista and tatiana are connected at their heads, whatever the girls do they do it together. in this case, brain images revealed that there was an attenuated line stretching between the two brains and forming a "thalamic bridge", a bridge connecting the two thalami. knowing that the thalamus acts as a major control panel within the body, it is believed that the girls share part of this control panel and so when one girl drinks the other one feels it. this along with many other cases, has advanced social media and neurological related research concerning this kind of link between craniopagus twins. unfortunately, no controlled studies have been done because the twins are so young and their brains are still very malleable and plastic. although there is not an overwhelming amount of research surrounding how the union between craniopagus twins leads to different personality, cognitive and motor traits, there have been some studies exploring what it actually means to share a brain. in the case of tatiana and krista, it is possible that the twins shared some conscious thought. studies of the thalamus’ role in the brain provide neurological data that help explain these behavioral observations that these two twins experience. thalamo-cortico-thalamic circuits are the looped neural pathways that connect the thalamus to the cerebral cortex, and then the cerebral cortex back to the thalamus. because the thalamus is mainly responsible for relaying sensory messages from the body to the brain, it is possible that there is a lot of overlap between the twins’ sensory reception and the actual response it creates within the brain. one study examines this by studying the thalamus when it is at a persistent vegetative state that is when the patient is awake but not conscious. this study proved that the cortical activity on its own is not conscious and that all the activity between the loops of the thalamus, the cerebral cortex and the thalamus itself are all conscious actions. another study of the thalamus reaffirms that the thalamus does not answer yes/no questions but instead acts as a mediator between different parts of the cerebral cortex and systemic sensory reception. these loops actually may account for the relationship between tatiana and krista. at the neuronal level, communication is dense network of neurons linked between themselves and the coordinator (in this case the thalamus) that finally sends a message to the cortex. on top of this, there are links between the cortex that send messages back through the coordinator and finally to the rest of the body. the brain's ability to function through loops and circuits is a good model to explain why tatiana “consciously” feels what krista is “physically” experiencing. additionally there is some level of synchronization between the two twins. another study found that for craniopagus twins, their connection to each other is comparable to our normal appendages and that their bodies have obvious overlapping physically and psychologically. because most cases of craniopagus twins are unique, the research outlining general connections between craniopagus twins is limited. however, this example provides insight into the effects of a union between twins who essentially share the same sensory relay system in the thalamus. history conjoined twinning is one of the oldest known birth defects in history and examples with human's fascination with twins is extremely evident throughout historical literature. although there are cases of conjoined twins dating back to as early as the 10th century, it was not until 1491 that the first case was documented. apart from that, sebastian münster’s cosmographia universalis provides the true first account of craniopagus twins who happened to live for ten years, exceeding many expectations during that time. he describes the set of twins as being a unique malformation and a punishment from their mother's mistake. in french barber surgeon ambroise paré’s 16th-century book, on monsters and marvels, various types of "supernatural" twinning are illustrated and described as "monstrous and marvelous creatures that proceed from the judgment of god", suggesting that conjoined twins and specifically craniopagus twins were viewed as literal monsters in the 16th century.