The Twins Who Share A Brain

Channel 4 recently broadcast an interesting documentary as part of their 'Bodyshock' series, dealing with a set of twins who are joined at the head. I wrote some notes while watching the documentary:

Tatiana and Krista Hogan are regarded as a 'medical marvel'. While instances of twins being born joined at the heads are rare, ithis particular case is certainly a marvel in living memory. Their mother, Felicia Hogan, discovered this information at her 21-week scan. As she was 21 years of age at the time and already had two older children, the medical staff offered her the option to have a termination in view of the weight of responsibilities she would have if she went through with the birth. Felicia opted against the offer and, at the time of birth, doctors were surprised at the survival of both mother and babies. They also noticed something strange: when one twin was injected, the other spontaneously cried. Further observations from family as the twins were growing up, such as one twin 'zoning out' when looking at something while the other twin's eyes twitched, made them speculate as to whether the twins shared senses.

How could this be possible? Four months after the twins were born, they underwent a CT scan to check for any indications. It was found that they shared brain matter and arterial structures in an interconnected fashion, so there could be no possibility of surgical separation as sometimes occurs in other cases of conjoined twins. Furthermore, it was discovered that both twins shared the same thalamus, which is the brain structure responsible for processing sensory inputs and relaying them to other structures - a communications control room.

(Tatiana, bottom left, and Krista, bottom right, with their mother Felicia, top left.
Image courtesy: Macleans.ca)

The documentary followed the progress of the Hogan twins over the course of a year or so. At around age 2 years and 4 months, the twins weren't able to walk but could stand with support, and had begun to talk using simple expressions like "stop that!" in response to stimulation. Also, it was possible to see the birthing of two distinct personalities.

Tatiana's qualities include being the more "intellectual" of the two (whatever that means for a 2 year old child!), and is very loving, engages in frequent hugging and kissing behaviours, of a happy disposition. By contrast, Krista, who can also be loving and happy, tends to be more hot-tempered, exhibiting protest (crying) behaviours and is more aggressive, will scream to get what she wants and can even be a bit of a "bully" according to Felicia. However, separate personalities though they are, they are already beginning to learn the value of cooperation and they work together on simple tasks such as coordinating movement to stand up and attempt to walk. If you tickle Krista, Tatiana giggles.

Some of the usual medical problems affecting many pairs of conjoined twins also affect the Hogans. Despite being smaller and thinner, Tatiana's heart pumps for both of them and is thus at risk of enlargement and possible failure. Tatiana's heart also works twice as hard to supply the brain's arterial system with blood. Over time, her heart rate has thankfully dropped and is much closer to Krista's, but the possibility of further complications as the twins age always looms.

It was also discovered that when the twins slept, Tatiana would stop breathing for up to 20 seconds. A surgical operation was needed to remove the huge adenoids that were causing the problem, but when Tatiana was anaesthetised it was observed that she was borrowing a large amount of blood to keep her going. The trouble with this was that Krista didn't have enough blood to be anaesthetised herself, which meant she had to be awake (and suffer pain?) when Tatiana went under the knife.

The rest of the documentary focused largely on the Hogan family's meeting with another pair of craniopagus twins, Lori and George Schappell, who are also joined at the head but have separate brains. The Schappells have enjoyed fame to an extent by appearing on a variety of talk shows, television dramas and singing contests, and were able to discuss their situations and give advice for the Hogans in matters of parenting and how to engage the Hogan twins in relationship skills.

At a later date, further tests were carried out to investigate further the possibility of shared senses. They concluded that the "brain of one twin records signals from the other's visual field". The explanation proffered for this told about how images entering the eyes of a twin travel along a "neuron highway" to the other's visual cortex, meaning that one twin can see what the other witnesses. Fascinating.