The case studied by the researchers of Padua
WY is 54 years old, 13 years of education, a normal life. In 2014, after an episode of postural instability and disorientation followed by a loss of consciousness, she undergoes an MRI. Result: she discovers that she has a tumor in the left hemisphere of the brain. It seems like a story like many others, but it isn’t. WY’s is “the strange case” of a right-hander who uses the left, as Italian scientists have described him in a study published in the journal ‘Cortex’. Man has always been right-handed. But, although he can still use his right arm perfectly as he is not affected by basic motor deficits, after the onset of the tumor he became left-handed / ambidextrous.
The study bears the signature of researchers from the University of Padua and the Padua hospital, coordinated by Konstantinos Priftis. “90% of the population is right-handed, that is, the left hemisphere of the brain is mainly involved in the use of the limbs, but more than a clear distinction it can be said that what drives us to use one limb rather than another is the presence of dedicated brain circuits that make us aware of our actions “, reads the note released by the university on the published scientific work. However, if there are lesions in one brain hemisphere, the team notes, there may be variations in the use of one or the other limb.
In the study, the researchers analyze the very rare case of WY. The tumor diagnosed in 2014 in the left hemisphere is to date in a non-evolving state. “The patient is affected by a neuropsychological disorder called motor neglect, whereby the spontaneous intentions to act through the opposite limb to the brain injury (in this case the right dominant limb) are lost – explains Priftis, of the Department of General Psychology of the University of Padua – Being right-handed is certainly determined by genetics, but it is something that must be continually updated by brain circuits that activate motor activities. If the brain circuits are affected by an injury, a genetically right-handed person can become left-handed / ambidextrous , as we observed in the case studied “.
The patient, whose muscular strength is intact, while continuing to use his right hand for writing, placed in front of various manual operations, uses both hands indifferently, even with a preference for the left hand.
“In the literature there are many cases with left motor neglect (meaning the left limbs) following a right brain injury – continues Priftis – If the patient is right-handed, left motor neglect makes the patient even more right-handed, that is the patient ignores the left limb and uses the right limb even more. Cases with right motor neglect following left brain injury (leading to acquired left-handedness) are very rare. There are only two detailed cases reported in the literature: in both cases cases the deficit had disappeared within a few months after the onset of the lesion. Our case is the only one described, to date, which still presents the phenomenon many years after the onset of the lesion “.
The study goes beyond the single history of the right-handed patient who found himself left-handed, but also represents a further cognitive step regarding the motor functions of the brain areas and opens up new scenarios on the understanding of motor deficiencies related to brain injuries and how they can modify manual preference.