When your right hand doesn't agree with your left…

blocking the movement and forcing you to turn right! This was a frustrating reality for one atypical patient whose case was presented in the online review Frontiers in Human Neuroscience. The patient, who was followed by a medical team in Marseille, was suffering from diagonistic dyspraxia or a conflict between his right and his left hand. But what made his case unique?

These types of behavior, also known as ‘diagonistics’, are principally observed in epileptic patients who have undergone surgery to sever the corpus callosum either partially or completely. This operation is usually used to treat refractory epilepsy by stopping interference between the left and the right hemisphere of the brain. Indeed, the corpus callosum (CC) is the bridge that connects the two parts of the brain, allowing information to pass from one side to the other. But the patient in question had never undergone surgery to the corpus callosum, because he didn’t have one!

According to the authors of the study, A.M. was the first case of diagonistic dyspraxia in a patient who had complete agenesis (the absence of an organ which did not form during embryogenesis) of the CC. This anomaly may not cause inter-hemispheric disconnection “split-brain” symptoms as the brain develops compensatory measures using other pathways between the two hemispheres, called “commissures.” In this case, patients can show good cognitive functioning as well as normal adaptation to social, familial and professional environments. A team led by Professor Olivier Felician, in association with neurologists from the Henri-Gastaut Hospital (Marseille), as well as researchers from the CNRS of the Center for Magnetic Resonance in Biology and Medicine (CRMBM) and the INSERM of The Institute of Neuroscience Systems (Aix Marseille University) had been following the case of A.M. since 2011.

A.M. was employed by the local council as a gardener. He had been suffering from temporal lobe epilepsy for over twenty years, which had been relatively well controlled with the aid of antiepileptic drugs. However, in March 2012, following an ENT infection, he suffered repeated epileptic seizures which damaged the transfer of information between the brain’s two hemispheres. One month later, when his seizures had stopped, A.M. started to show signs of diagonistic dyspraxia of the right hand, which involved a series of embarrassing and distressing behaviors. One day, while walking in his neighborhood, his right hand suddenly gripped a post, and for several minutes A.M. was left stuck to the post desperately turning around it! Another time, when he was putting on his pants with his left hand, the right one was trying to pull them down! And at a later time, his right hand swiped his wallet from his back pocket and his left hand had to battle with the right to try and get it back. These unpredictable and uncontrollable symptoms lasted for two years.

During this period the medical team in Marseille carried out a series of brain imagery tests to compare A.M.’s neuronal networks to those of 16 healthy patients. The results revealed a dysfunction of the pathways between the two hemispheres, particularly at the center of a neuronal network, the salience network. This part of the brain organizes information from the external world and from within our brains, selecting the most relevant and enabling us to act. As he was unable to make a selection, A.M. experienced great difficulty in inhibiting some grasping behaviors, which was why his right hand would grab objects in an unexpected and uncontrollable fashion.

Luckily, these symptoms started to become less frequent in September 2013, and completely disappeared during the 6 months prior to the final evaluation in September 2014.

A.M.’s left hand finally made peace with the right.
Source: Ridley B, Beltramone M, Wirsich J, Le Troter A, Tramoni E, Aubert S, Achard S, Ranjeva JP, Guye M, Felician O. Alien Hand, Restless Brain: Salience Network and Interhemispheric Connectivity Disruption Parallel Emergence and Extinction of Diagonistic Dyspraxia, in Frontiers in Human Neuroscience, June 2016.

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