Symptom profiles of right- and left-handers with neurodegenerative disease do not differ

Handedness is not significantly associated with cognition or neuropsychiatric symptoms in common neurodegenerative diseases or in cognitively healthy individuals at old age, a large study shows.

Researchers from the University of Helsinki and the University of Eastern Finland have investigated the effect of handedness on cognitive functions and neuropsychiatric symptoms in people with Alzheimer's disease, dementia with Lewy bodies or frontotemporal dementia. The study also included cognitive healthy individuals.

"There has been extensive research on factors affecting the symptomatology of memory disorders, but surprisingly little attention has been paid to handedness. The topic is relevant, because in the early stages of dementia, neurodegenerative changes are often more pronounced in one hemisphere of the brain" says Postdoctoral Researcher Toni Saari who conducted the study.

In the study, about 8% of cognitively healthy individuals were left-handed and 2% ambidextrous and the proportions were very similar in those with neurodegenerative diseases.

The study found no clear differences between right- and left-handed people either in cognitive functions or in neuropsychiatric symptoms. The results were similar in all disease groups, even though the diseases are characterised with different brain pathologies and symptoms.

The results are based on a study cohort of more than 30 000 individuals from the United States. The work is the largest study on the effect of hand preference on cognition and neuropsychiatric symptoms in common neurodegenerative diseases conducted to date.

"Considering individual neuropsychological tests, the differences between right and non-right-handers are so small that they do not have clinical relevance when assessing cognitive function in neurodegenerative diseases," says Saari, summarising the clinical significance of the study.

"Progressive diseases causing dementia in old age impair cognition and can cause neuropsychiatric symptoms, but our results show that the effects are similar regardless of hand preference. However, future work should investigate whether so-called forced right-handedness plays a role in the symptomatology of memory disorders. The dataset we used did not have this information," adds Academy Research Fellow Eero Vuoksimaa who led the study.

The study has received funding from the Academy of Finland.

Original publication:

Brain Communications, fcad137, DOI:10.1093/braincomms/fcad137